Tag Archives: venom

Endangered, Bird-eating Centipedes of Mauritius

Can a centipede really be endangered? Of course!

Centipedes don’t get much love, even from each other. They are solitary, irritable, fiercely cannibalistic, and arguably some of the most widely hated animals on earth. I know many biologists who would gladly handle a snake or tarantula, but shudder at the thought of a giant centipede creeping up their arm.

An Indopacific centipede, making good use of a hole in the wall. Photo by Thomas Brown, licensed under CC BY 2.0.

An Indopacific centipede, making good use of a hole in the wall. Photo by Thomas Brown, licensed under CC BY 2.0.

I never begrudge people for being scared of centipedes. They are objectively frightening: many-legged, venomous, fast-moving, and secretive. In the rural tropics, a painful bite from a giant centipede is a very real possibility. But none of this means they can’t be endangered, put at risk of extinction either by natural circumstance or by human activity.

Unsurprisingly, very few centipedes have ever been studied from a conservation-oriented perspective. Most of the time, there simply isn’t the funding, public interest, or lack of squeamishness to make that kind of research happen. There are, however, exceptions. Today I’m going to tell you about one: the giant centipedes of Mauritius and Rodrigues.

Mauritius, Rodrigues, and their satellites form a collection of tiny islands in the Indian Ocean, just a few thousand miles east of Madagascar. Like most islands they have a long, sad history of extinctions wrought by over-hunting, invasive species, and habitat destruction. The dodo bird, native to Mauritius, was one of the first victims.

Mauritius.png

Mauritius, in panoramic view. Photo by Clément Larher, licensed under CC BY-SA 3.0.

The two main islands are home to two species of giant centipede, the blue-legged (Scolopendra morsitans) and the Indopacfic (Scolopendra subspinipes) centipedes*. Both species are incredibly efficient predators, and with body lengths of 8 inches or more, they are more than capable of tackling large prey such as mice. On Mauritius, staple fare include house geckos and cockroaches, but they also take day-old chicks from their nests when opportunity strikes (Lewis et al. 2010). The Indopacific centipede can even swim, undulating side-to-side while holding its head above the surface like a crocodile (Lewis 1980).

Despite their size, venom, and general badassness, giant centipedes are prey for many larger animals. On Mauritius, they form 80% of the diet of feral cats that roam the island by night. The cats are apparently nimble (and daring) enough to tear apart the centipedes without getting bitten.

An Indopacific centipede from China. Photo by Thomas Brown, licensed under CC BY 2.0.

An Indopacific centipede from China. Photo by Thomas Brown, licensed under CC BY 2.0.

Even in the face of predation by cats, giant centipedes remained abundant until 1997, when a new invasive species came into the picture. That species was the musk shrew (Suncus murinus), introduced from India. A smaller shrew might become prey for a centipede, but the musk shrew is the largest in the world, reaching a length of 6 inches or more.

An 8-inch-long centipede is still a formidable adversary, but the shrews were used to encountering giant centipedes in their native range (as it happens, the Indopacific centipede also lives in India). They have made short work of centipede populations, which are now greatly reduced (Lewis et al. 2010). The Indopacific centipede is now found on Rodrigues, but no longer on Mauritius, while the blue-legged centipede is still found on both islands.

Mauritius and its satellite islands. From Lewis et al. (2010), licensed under CC BY 4.0.

Mauritius and its satellite islands. From Lewis et al. (2010), licensed under CC BY 4.0.

I am not about to launch into a passionate defense of blue-legged and Indopacific centipedes. As I said before, both species are abundant in tropical habitats all over the world, from Indonesia to the Caribbean. For all we know the centipedes themselves are invasive, dancing with cats and shrews on the graves of long-gone native species. Instead this article is about another giant, a third centipede, gone from Mauritius but still clinging to life on Serpent Island.

Serpent Island is a satellite of Mauritius, uninhabited by humans and with an area less than 100 acres. There is very little vegetation or soil there, and bare rock dominates the surface. In the absence of humans or large predators, sea birds thrive, especially sooty terns which nest by the thousands on open ground.

They share the space with centipedes — not Indopacific or blue-legged, but Serpent Island giant centipedes (Scolopendra abnormis), which are found on one other satellite island (Round Island) and nowhere else on earth — not even Mauritius. The centipedes are abundant on Serpent Island, with roughly 12 individuals per square meter. If centipedes frighten you, don’t plan your next vacation here.

During the day centipedes hide beneath rocky slabs and underground, away from the light and from watchful, easily enraged mother birds. Terns are active during the day, flying from land to sea and back again, gathering fish for their hungry chicks. With all the traffic, a centipede is better off staying out of sight.

A sooty tern. Photo by Duncan Wright, in public domain.

A sooty tern. Photo by Duncan Wright, in public domain.

By night the terns are less wary. Snakes, which would normally prey on tern chicks, are absent from the island, probably driven out soon after the arrival of European explorers. Without the competition, centipedes have risen to take their place. Wandering over the rocks, a centipede uses smell and touch to locate a nest, grab hold of a chick, and sink in its venom-laden fangs. More than any so-called bird-eating tarantula, the Serpent Island centipede is a true bird-eater. In captivity, they can survive for several years on a diet of chick legs (Lewis et al. 2010).

The taste for bird meat is probably a recent acquisition — Serpent Island centipedes most likely colonized the island only a few million years ago. They would have arrived from Mauritius, suggesting the larger island had a population of Serpent Island centipedes before they were driven to extinction by the introduced shrews, cats, and perhaps larger centipedes.

The Serpent Island centipede is classified as Vulnerable by the International Union for Conservation of Nature (IUCN 2012). This means the species is  “considered to be facing a high risk of extinction in the wild.” It is one of 10 potentially threatened centipedes on the IUCN Red List (of 3,300 total centipede species worldwide). So far, none have been given legal protection.

Centipede snacks. Photo by Duncan Wright, in public domain.

Centipede food. Photo by Duncan Wright, in public domain.

The bad news is that, if shrews or cats or rats were to be introduced to Serpent Island, the entire ecosystem would collapse. Invasive predators would quickly eat both chicks and centipedes, leaving Serpent Island a bare rock in the middle of the ocean, with a few tufts of grass and the occasional cockroach.

The good news is that centipedes are abundant in their last remaining habitats, with an estimated population of 10-15,000. Serpent Island is remote and protected, and biologists are pretty much the only visitors, so it is unlikely shrews will ever get there. The future of Serpent Island’s bird-eating centipedes is secure, for now.

Reminder: there are still 6 days left to donate to Dr. Adam Britton’s crowdfunding campaign to study threatened pygmy crocodiles in Australia! I’ve donated, and I encourage you to so if you think pygmy crocodiles, which you can read about here, are awesome, which of course they are. There are some amazing prizes for donors, including crocodile-themed artwork and jewelry!

*These species normally go by the common names Tanzanian giant (blue-legged) and Vietnamese giant (Indopacific). However, both are extremely wide-ranging in tropical habitats all over the world, including Hawaii where they have been introduced by humans (Shelley et al. 2014). To reduce confusion I used alternative common names.

Cited:

IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. Gland, Switzerland and Cambridge, UK: IUCN. iv + 32pp.

Lewis J.G.E., P. Daszak, C.G. Jones, J.D. Cottingham, E.Wenman, and A. Maljkovic. 2010. Field observations on three scolopendrid centipedes from Mauritius and Rodrigues (Indian Ocean) (Chilopoda: Scolopendromorpha). International Journal of Myriapodology 3: 123-137.

Lewis J.G.E. 1980. Swimming in the centipede Scolopendra subspinipes Leach (Chilopoda, Scolopendromorpha). Entomologists Monthly Magazine 116: 219-220.

Shelley R.M., W.D. Perreira, and D.A. Yee. 2014. The centipede Scolopendra morsitans L., 1758, new to the Hawaiian fauna, and potential representatives of the “S. subspinipes Leach, 1815, complex” (Scolopendromorpha: Scolopendridae: Scolopendrinae). Insecta Mundi 338: 1-4.

Are Tarantulas Dangerous? Most Aren’t, A Few Might Be

Of the 900 or so known tarantula species, almost all are harmless (Isbister et al. 2003, Lucas et al. 1994). A bite by any large spider can be painful even if no venom is injected, since the fangs themselves are essentially big needles. Even if venom is injected, however, most tarantula bites result in little more than local pain and swelling. When there are medical problems, the cause is usually shock or an allergic reaction, rather than the action of the venom itself.

The Chilean rosehair tarantula (Grammostola rosea), a hardy and docile pet. Photo from Insects Unlocked, in public domain.

The Chilean rosehair tarantula (Grammostola rosea), a hardy and docile pet. Photo from Insects Unlocked, in public domain.

That said, not all tarantulas are equally venomous. The most common tarantulas sold in pet shops are all pretty benign: the Chilean rose hair, the Mexican redknee, and the pinktoe tarantulas have both mild venom and docile habits. They can be handled gently with almost no risk of being bitten.

Other, more exotic species kept by seasoned tarantula experts include the cobalt blue, the goliath birdeater, and the golden starburst tarantulas. These are beautiful and impressive captives — the goliath birdeater can attain a 12-inch leg span. The cobalt blue and golden starburst are stunningly colorful animals, the latter approximately matching the color of Donald Trump’s hair. These species are also more nervous and willing to bite, and their bites are generally more painful (e.g., Takaoka et al. 2001).

The golden starburst tarantula (Pterinochilus murinus), guarding its silken retreat. Photo by Stefan Walkowski, licensed under CC BY-SA 3.0.

A golden starburst tarantula (Pterinochilus murinus) guarding its silken retreat. Photo by Stefan Walkowski, licensed under CC BY-SA 3.0.

Avid tarantula enthusiasts don’t get most of their spiders from pet shops. Instead they buy tarantulas from other spider-keepers who breed their pets, or from companies that import spiders and other animals from around the world. With international trade, hundreds of species are available for hobbyists collect. Many of these are poorly known, most have not had their venom studied, and a few haven’t even been formally described by scientists.

Where venomous animals are concerned, gaps in scientific knowledge can have serious consequences. A few years ago a Swiss man was bitten by one of his many pet tarantulas — at first, the only symptoms were mild pain, hot flushes and sweating. He brought himself to the hospital 15 hours later, when he began to experience severe muscle cramps and stabbing chest pain. Doctors gave him medication (midazolam and lorazepam) that reduced the symptoms, but muscle cramps did not disappear completely until three weeks after the bite (Fuchs et al. 2014). The tarantula in this case was a regal ornamental tarantula, a magnificent tree-dwelling spider native to India.

A regal ornamental tarantula (Poecilotheria regalis). Photo by Morkelsker, in public domain.

A regal ornamental tarantula (Poecilotheria regalis), with a leg span up to 6 inches. Photo by Morkelsker, in public domain.

There are at least 16 species of ornamental tarantulas, all from tropical forests in India and Sri Lanka. Most of them can be found in the exotic pet trade, and many have become popular with tarantula keepers looking for something a little more exciting. Exciting is certainly what they get: ornamental tarantulas are stunningly beautiful, as well as extremely fast and agile climbers. They are also quick to bite if cornered. Ornamental tarantula venom, while not deadly, is certainly underestimated.

To see if muscle cramps and chest pain were common symptoms of ornamental tarantula bites, Joan Fuchs and colleagues (2014) looked at 26 case reports, most of which were blog entries by seasoned tarantula keepers and breeders. Of the cases, 58% involved muscle cramps, along with other symptoms such as fever and heavy breathing. A few patients even lost consciousness for short periods. All bites were painful, but those that led to muscle cramps were severely so. This led the researchers to believe that, in cases where muscle cramps did not appear, the spider had simply injected much less venom.

The metallic ornamental tarantula (Poecilotheria metallica). Photo by Søren Rafn, licensed under CC BY-SA 3.0.

The metallic ornamental tarantula (Poecilotheria metallica). Photo by Søren Rafn, licensed under CC BY-SA 3.0.

It’s worth remembering that no tarantula bite has ever been fatal. It is a sorry fact, however, that by far the greatest source of knowledge on tarantula bites comes not from scientists, but from spider-keepers who take great pains (literally) to record their symptoms after every bite. This information is shared with other spider-keepers online at websites like Arachnoboards, so other hobbyists know what to expect from each species.

Such informal reports have been done for many species that have yet to be studied closely by scientists, and some that haven’t even been “discovered” (i.e., been given Latin names and formally described). The scientific axiom that “more work is needed” may be a cliché, but regarding tarantula bites and spider venom in general, it is certainly true.

Cited:

Fuchs J., M. von Dechend, R. Mordasini, A. Ceschi, and W. Nentwig. 2014. A verified spider bite and a review of the literature confirm Indian ornamental tree spiders (Poecilotheria species) as underestimated theraphosids of medical importance. Toxicon 77: 73-77.

Isbister G.K., J.E. Seymour, M.R. Gray, and R.J. Raven. 2003. Bites by spiders of the family Theraphosidae in humans and canines. Toxicon 41(4): 519-524.

Lucas S.M., P.I. Da Silva Júnior, R. Bertani, and J.L. Cardoso. 1994. Mygalomorph spider bites: a report on 91 cases in the state of São Paulo, Brazil. Toxicon 32(10): 1211-1215.

Takaoka M., S. Nakajima, H. Sakae, T. Nakamura, Y. Tohma, S. Shiono, and H. Tabuse. 2001. Tarantulas bite: two case reports of finger bites from Haplopelma lividum. The Japanese Journal of Toxicology 14(3): 247-250.

Recluse Spider Venom: How it Works

by Joseph DeSisto

Poisons and venoms often contain hundreds of different chemicals, each with a special role. When venom is dangerous to humans, it is useful to know which of the molecules involved is causing harm. In the case of the blue-ringed octopus, tetrodotoxin is the culprit, paralyzing your nervous system and keeping you from breathing. Cobras and sea snakes accomplish roughly the same thing with a whole suite of neurotoxins. Vipers, on the other hand, use hemotoxins to destroy blood vessels and force clots to develop, so oxygen can’t reach the cells that need it.

A brown recluse (Loxosceles reclusa). Photo by the Smithsonian Institution Insect Zoo, licensed under CC BY-NC 2.0.

A brown recluse (Loxosceles reclusa). Photo by the Smithsonian Institution Insect Zoo, licensed under CC BY-NC 2.0.

Brown recluse venom is far less dramatic. As in all spiders, the primary purpose of venom is to kill and digest insects or other prey, but recluse spiders and their relatives (members of the family Sicariidae) have a protein that does something special. That protein is called sphingomyelinase D – we’ll call it SMD. Exactly what SMD does when injected into insects isn’t clear, but when it enters a person via a spider bite, the protein may cause the tissue around the bite to die and form a necrotic lesion. In extremely rare cases, SMD can be carried by the bloodstream to other parts of the body, causing illness or even death.

Recluses and their cousins, the sand spiders (genus Sicarius), belong to the family Sicariidae or six-eyed spiders, which includes all the 132 spiders that use SMD in their venom (Binford and Wells 2003). No other animals are known to produce SMD, but there are bacteria that make it, and it just so happens that all of these bacteria are known to cause infections in humans (Binford et al. 2005).

A brown recluse spider with a penny. Photo by the Smithsonian Institute Insect Zoo, licensed under CC BY-NC 2.0.

A brown recluse spider with a penny. Photo by the Smithsonian Institute Insect Zoo, licensed under CC BY-NC 2.0.

One of them is Clostridium perfringens. Chlostridium is a genus of bacteria with around 100 species, all but five of which are completely harmless. See the layer of dust at the back of your desk? Run your finger through it – write your name, or make a smiley face. Now look at the dust that’s gathered on your fingertip. Chances are you’ve just collected some Clostridium, which is also found in soil, water, plants, and the digestive systems of animals. Clostridium spores are virtually indestructible, so the bacteria can contaminate just about any surface. Since the vast majority of species are harmless, that isn’t much of a problem.

Five, however, can cause serious illness in humans. The best-known is Chlostridium botulinum, which makes a poison called botulinotoxin and causes, as you might have guessed, botulism. C. perfringens, meanwhile, can cause food poisoning and gangrene using, among other proteins, SMD. Here’s where the plot thickens: Brazilian researchers discovered in 2002 that perfringens often lives in the venom glands of recluse spiders, manufacturing SMD alongside the spider’s own arsenal of venom-producing cells (Monteiro et al. 2002).

The same scientists then tested the strength of the spiders’ venom on rabbits, using spiders with and without bacterial “infections.” As expected, spider bites led to bigger lesions when bacterial colonies were present in the spider’s fangs, suggesting these bacteria might actually help the spiders by making their venom stronger. In return, the bacteria get a relatively safe place to multiply, within their host’s venom glands.

A sand spider (Sicarius) from the Namib Desert in southwestern Africa. Photo by Jon Richfield, licensed under CC BY-SA 3.0.

A sand spider (Sicarius) from the Namib Desert in southwestern Africa. Photo by Jon Richfield, licensed under CC BY-SA 3.0.

Recluse spiders aren’t unique in using bacteria to help manufacture toxins. Pufferfish, for example, wouldn’t be poisonous if it weren’t for tetrodotoxin-producing bacteria that live within their skins and livers. What’s different about the recluse-bacteria relationship is that neither party truly depends on the other – perfringens bacteria can easily find shelter elsewhere, and recluse spiders can make plenty of SMD without the microbial help, thank you very much.

The gene that allows for SMD in both spiders and bacteria reveals that life was not always so. Instead, more than 150 million years ago, an enterprising spider stole the bacteria’s SMD-making genes and inserted them into its own DNA toolkit (Binford et al. 2005). That spider did very well — all of today’s six-eyed spiders, the SMD-producing recluses and sand spiders, are descended from that individual.

Bacteria aside, all recluses are not equally dangerous to humans. The North American brown recluse (Loxosceles reclusa) is relatively tame: bites are very rare, to the point that 80% of alleged recluse bites aren’t actually recluse bites (Swanson and Vetter 2005). A review of “suspected” brown recluse bites revealed that around a third of bite victims developed lesions, 14% fell ill, and none died or suffered serious complications (Wright et al. 1997). The United States is also home to five other recluse species, none of which are known to be harmful to people.

The Arizona recluse spider (Loxosceles arizonica). Photo by Sean McCann, used with permission.

The Arizona recluse spider (Loxosceles arizonica). Photo by Sean McCann, used with permission.

Travel to western South America and the story changes. The Chilean recluse (Loxosceles laeta) is the most dangerous of the recluse species, partly because it likes to live in and around buildings. In Spanish it goes by the name araña de rincón, which means “corner spider,” after this spider’s habit of finding shelter in the secluded, dusty corners of old homes. Even though Chilean recluses are not especially aggressive, their preferred habitats makes encounters with humans very likely, and a few bites each year are inevitable.

Bites from Chilean recluses are also more toxic than those of their northern cousins. A survey of bite cases found that 84% of people developed lesions, 15% fell ill, and 3.7% died (Schenone et al. 1989). A 3.7% death rate sounds pretty scary, but this was in 1989 – medical care has improved since then, and spider antivenom today is much more widely available (Lucas 2015).

The eyes and fangs of a Chilean recluse -- note the six eyes, a characteristic of sicariid spiders. Photo by Ken Walker, licensed under CC BY 3.0 AU.

The eyes and fangs of a Chilean recluse — note the six eyes, an important feature of sicariid spiders. Photo by Ken Walker, licensed under CC BY 3.0 AU.

Sand spiders also possess SMD and can cause lesions in humans. Yet despite sand spider venom being far more toxic than most recluse venoms (Van Aswegen et al. 1997), no human deaths have ever been reported. Why? Because sand spiders, unlike recluses, don’t tend to live in places where human encounters are likely. Instead they inhabit remote desert regions of South America and Africa. Even though sand spiders have some of the most powerful venoms of any spiders, loaded with SMD, but bites are extremely rare and the worst cases have only resulted in lesions similar to those caused by recluse bites (Lopes et al. 2013)

Millions of years of desert living have hardened the sand spiders – some species can live longer than a decade. Opportunities to catch prey in the desert are rare, so strong venom might help reduce the spiders’ error rate. Sand spiders are also experts at camouflage, often covering their bodies with sand to disguise their bodies in a barren landscape.

The Brazilian sand spider (Sicarius ornatus), camouflaging itself with sand. Photo from Lopes et al. (2013), licensed under CC BY 4.0.

The Brazilian sand spider (Sicarius ornatus), camouflaging itself with sand. Photo from Lopes et al. (2013), licensed under CC BY 4.0.

So what’s the difference? Why are some recluses and sand spiders more toxic than others? Since among all the proteins in recluse and sand spider venom, SMD is the one that causes harm to humans, it makes sense that spiders with higher levels of SMD in their venom are more dangerous. Specifically, we would expect the sand spiders and the Chilean recluse to have more SMD in their venom than the other, less dangerous recluse spiders. But how to test our theory?

The first step: extracting venom from recluses and sand spiders, which is easier than you might think. Scientists at the University of Arizona (Binford and Wells 2003) did this by knocking out spiders with carbon dioxide, then shocking their fangs with tiny electrodes. The minute electric shock caused the unconscious spiders to release all their venom into tiny vials, which could then be stored in a -80̊ C freezer. The same technique works for extracting venom from all kinds of animals, from rattlesnakes to scorpions to honey bees.

Next comes measuring the SMD levels in venom from each species — in this experiment, ten recluses and two sand spiders. The results were surprising in that the sand spider and Chilean recluse venoms had moderate concentrations of SMD — no greater or smaller than those of the other spiders. Instead, these three differed from the others in another regard.

A brown recluse from Kansas. From Saupe et al. (2011), licensed under CC BY 4.0.

A brown recluse from Kansas. From Saupe et al. (2011), licensed under CC BY 4.0.

They had more venom by, on average, nearly seven times. Usually, large spiders have more venom than smaller ones, but all the spiders in this experiment are roughly the same size. Why the sand spiders and the Chilean recluse should have so much more venom than their relatives is unknown for practical purposes, it doesn’t really matter. What matters is that, even if SMD concentrations are about equal, sand spiders and Chilean recluses still have seven times more SMD than any of the other recluses.

Venoms and poisons are bewilderingly complicated. They’re also amazing, and locked within each molecule are incredible opportunities to understand the natural world, improve medical care, and even save lives. When the diversity of life on earth meets the diversity of biochemistry, it’s clear that studying these amazing substances will keep scientists occupied for as long as there are spiders, hiding in corners and striding across the sand.

Thanks are owed to Sean McCann, who gave me permission to use his photograph of an Arizona recluse (Loxosceles arizona), rarely seen in the United States. You can check out more of his photography at his website, http://ibycter.com/.

Catherine Scott, a PhD student and arachnologist at the University of Toronto, maintains a blog devoted to spider biology. She wrote a fantastic article on identifying brown recluses, which you can read here. You can also follow her on twitter (@Cataranea) and inquire about spiders you think might be brown recluses.

Cited:

Binford G.J., M.H.J. Cordes, and M.A. Wells. 2005. Sphingomyelinase D from venoms of Loxosceles spiders: evolutionary insights from cDNA sequences and gene structure. Toxicon 45: 547-560.

Binford G.J. and M.A. Wells. 2003. The phylogenetic distribution of sphingomyelinase D activity in venoms of Haplogyne spiders. Comparative Biochemistry and Physiology Part B 135: 25-33.

Lopes P.H., R. Bertani, R.M. Gonalves-de-Andrade, R.H. Nagahama, C.W. van den Berg, and D.V. Tambourgi. 2013. Venom of the Brazilian spider Sicarius ornatus (Araneae, Sicariidae) contains active sphingomyelinase D: potential for toxicity after envenomation. PLoS Neglected Tropical Diseases 7(8): e2394. doi: 10.1371/journal.pntd.0002394

Lucas S.M. 2015. The history of venomous spider identification, venom extraction methods and antivenom production: a long journey at the Butantan Institute, São Paulo, Brazil. Journal of Venomous Animals and Toxins Including Tropical Diseases 21: 21.

Monteiro C.L.B., R. Rubel, L.L. Cogo, O.C. Mangili, W. Gremski, and S.S. Veiga. 2002. Isolation and identification of Clostridium perfringens in the venom and fangs of Loxosceles intermedia (brown spider): enhancement of the dermonecrotic lesion in loxoscelism. Toxicon 40: 409-418.

Saupe E.E., M. Papes, P.A. Selden, and R.S. Vetter. 2011. Tracking a medically important spider: climate change, ecological niche modeling, and the brown recluse (Loxosceles reclusa). PLoS ONE 6(3): e17731. doi: 10.1371/journal.pone.0017731

Schenone H., T. Saavedra, A. Rojas, and F. Villarroel. 1989. Loxoscelism in Chile: epidemiological, clinical, and experimental studies. Revista do Instituto de Medicina Tropical de São Paulo 31(6): 403-415.

Swanson D.L. and R.S. Vetter. 2005. Bites of brown recluse spiders and suspected necrotic arachnidism. The New England Journal of Medicine 352: 700-707.

Van Aswegen G., J.M. van Rooyen, D.G. van der Nest, F.J. Veldman, T.H. de Villiers, and G. Oberholzer. 1997. Venom of a six-eyed crab spider, Sicarius testaceus (Purcell, 1908) causes necrotic and haemorrhagic lesions in the rabbit. Toxicon 35(7): 1149-1152.

Wright S.W., K.D. Wrenn, L. Murray, and D. Seger. 1997. Clinical presentation and outcome of brown recluse spider bite. Annals of Emergency Medicine 30(1): 28-32.

Poison-Laced Silk

by Joseph DeSisto

The bivouac spider (Parawixia bistriata) is ordinary in appearance, brown with a sagging and trapezoidal abdomen, but with one of the strangest behaviors of any spider. They are social, working together to build large webs between rainforest trees, but that isn’t the wierdest thing — other spiders are social, too. What’s really strange is that bivouac spiders are social during the daytime, but at night, retire from society to form individual webs (Wenseleers et al. 2013). They viciously defend these webs against other spiders, even their former collaborators.

Regardless of their odd social lives, bivouac spiders are otherwise typical orb-weavers, constructing spiral-shaped webs with many spokes, nested between branches and trunks. When a fly or moth lands on the web, the spider rushes out to quickly wrap its prey in silk before injecting a lethal dose of venom.

A related species of bivouac spider, Parawixia audax. Photo by Nicolas Olejnik, licensed under CC BY-NC 3.0.

A related species of bivouac spider, Parawixia audax. Photo by Nicolas Olejnik, licensed under CC BY-NC 3.0.

Spider venom contains hundreds of different toxic chemicals, ranging from simple molecules with just a few atoms to complex proteins. There are also more than 40,000 species of spider, each with its own unique combination of chemicals, and some with toxins found nowhere else in the animal kingdom. As a result, chemists who study spider venom often make unusual and surprising discoveries.

Bivouac spider venom was the first, and remains the only, spider venom known to contain a unique class of compounds called tetrahydro-β-carbolines (Cesar et al. 2005) — we’re going to call them THβCs because, frankly, I’m pretty sure you skipped over that word, and I don’t blame you. Complex chemicals often have long names, but that isn’t the fault of chemists. The diversity of chemicals in nature is simply so great that having nice, easy names for all of them is a laughable impossibility. In this respect, organic chemistry and biodiversity have a lot in common.

Anyway, back to venom. Finding THβCs was exciting because these molecules aren’t only found in spider venoms — they’re also found in a number of plants used as medicine by indigenous peoples from Asia to Africa to South America. Seed extracts from Syrian rue (Peganum harmala), a tiny flowering plant, have been used for hundreds of years in northern China to combat both malaria and throat cancer (Cao et al. 2007). Today, scientists are studying the THβCs found in the same plant, but in a laboratory setting — it turns out they really do have anti-malaria and anti-cancer properties.

Syrian rue for sale in a Kasakhstan market. Photo by Yuri Danilevsky, licensed under CC BY-SA 3.0.

Syrian rue for sale in a Kasakhstan market. Photo by Yuri Danilevsky, licensed under CC BY-SA 3.0.

THβCs are also powerful insecticides, and probably evolved as a way for plants to defend themselves against leaf-eating insects. These are, however, a diverse group of molecules and their effects can be variable. In the Amazon, THβC-laced plants are used as recreational drugs, causing hallucinations (Cao et al. 2007). The particular variety found in bivouac spider venom, dubbed PwTX-I, causes nervous convulsions in rats (Cesar-Tognoli et al. 2011). More important to the spiders, it kills insects instantly.

The presence of THβCs in bivouac spider venom is a beautiful example of convergent evolution: the same strategy evolving to solve the same problem, in multiple organisms. Both Syrian rue and bivouac spiders needed a way to kill insects (albeit for different reasons), and each evolved the ability to manufacture THβCs to do the job.

I said earlier that bivouac spiders are the only spiders known to use THβCs in their venom — technically, that’s true. There is, however, another orb-weaving spider that uses THβCs to dispatch its prey. That spider is the giant golden orb-weaver or “banana spider” (Nephila clavipes), a songbird-sized behemoth found throughout the tropical Americas. And yes, their silk really does shimmer gold in the right lighting.

The giant golden orb-weaver, with prey in her shimmering web. Photo by Victor Patel, licensed under CC BY-SA 2.5.

The giant golden orb-weaver, with prey in her shimmering web. Photo by Victor Patel, licensed under CC BY-SA 2.5.

These are big spiders that build big webs, with a silken spiral more than three feet across. The gold shimmer comes from a yellow, reflective substance called xanthurenic acid, which the spider weaves into its silk. In 2005, however, the same Brazilian scientists discovered these spiders were also lacing their webs with THβCs — not the same kind as the bivouac spiders, but a new molecule.

When a insect, such as a moth, hits a spider web, it immediately becomes stuck in a tangle of sticky threads. These threads are covered in oil droplets, which stick to and cover the insect. As the prey wrestles with the snare, it only becomes more hopelessly tangled. Normally, this is the point where an orb-weaver drops down and bites its prey, injecting venom, but a golden orb-weaver plans ahead. The oil droplets on its web are filled with THβCs, which seep into the insect’s body as it struggles.

In combination with another toxin (specifically an organometallic 1-(diazenylaryl) ethanol: see Marques et al. 2004), THβCs make short work of the trapped insect. If the spider is lucky, death sets in before she even has to move. This might cruel, but trapping prey is risky business. Insects in spider webs flail about, trying desperately to free themselves, and some have nasty weapons of their own. By killing its prey from a distance, without ever having to lift a leg, a golden orb-weaver can avoid risking injury to itself, increasing the chances that it will live to hunt another day.

A golden orb-weaver in Jamaica. Photo by Charles Sharp, licensed under CC BY-SA 4.0.

A golden orb-weaver in Jamaica. Photo by Charles Sharp, licensed under CC BY-SA 4.0.

This is the second in a series of articles exploring how animals use chemical weapons to capture prey and defend themselves. Instead of focusing on a particular animal, each article will focus on a particular chemical, and how it is used by a variety of creatures. The first article in the series explores tetrodotoxin and the newts, snakes, fish, caddisflies, sea slugs, and other animals that use it. To read that article, click here.

You might remember that in the second paragraph I mentioned that some spiders, including Parawixia, are social. It just so happens that I wrote an article on social spiders several weeks ago — you can read that by clicking here.

Cited:

Cao R., W. Pang, Z. Wang, and A. Xu. 2007. β-carboline alkaloids: biochemical and pharmacological functions. Current Medicinal Chemistry 14: 479-500.

Cesar-Tognoli L.M.M., S.D. Salamoni, A.A. Tavares, C.F. Elias, J.C. Da Costa, J.C. Bittencourt, and M.S. Palma. 2011. Effects of spider venom toxin PwTX-I (6-hydroxytrypargine) on the central nervous system of rats. Toxins 3(2): 142-162.

Marques M.R., M.A. Mendes, C.F. Tormena, B.M. Souza, S.P. Ribiero, R. Rittner, and M.S. Palma. 2004. Structure determination of an organometallic 1-(diazenylaryl)ethanol: a novel toxin subclass from the web of the spider Nephila clavipes. Chemistry and Biodiversity 1: 830-838.

Marques M.R., M.A. Mendes, C.F. Tormena, B.M. Souza, L.M.M. Cesar, R. Rittner, and M.S. Palma. 2005. Structure determination of a tetrahydro-β-carboline of arthropod origin: a novel alkaloid-toxin subclass from the web of spider Nephila clavipesChemistry and Biodiversity 2: 525-534.

Wenseleers T., J.P. Bacon, D.A. Alves, M.J. Couvillon, M. Karcher, F.S. Nascimento, P. Noguiera-Neto, M. Ribiero, E.J.H. Robinson, A. Tofilski, and F.L.W. Ratneiks. 2013. Bourgeois behavior and freeloading in the colonial orb web spider Parawixia bistriata (Araneae, Araneidae). The American Naturalist 182(1): 120-129.

Deadly Caterpillars

by Joseph DeSisto

Today’s article is about the hemileucines, caterpillars with venom-injecting spines. While most have harmless, if painful, stings, a few have venom powerful enough to kill an adult human. But before things get too dark, let’s take some time to appreciate some harmless little beasties:

First-instar caterpillars of the io moth (Automeris io), munching on some oak leaves. Photo by Shawn Hanrahan, licensed under CC BY-SA 2.5.

First-instar caterpillars of the io moth (Automeris io), munching on some oak leaves. Photo by Shawn Hanrahan, licensed under CC BY-SA 2.5.

These are the newly-hatched caterpillars of the io moth, found in eastern and central North America. As caterpillars, they like to move and feed in groups, which provides some protection against predators. The moth, with a wingspan approaching four inches, looks like this:

An adult io moth, ready to take flight and find a mate. Photo by Patrick Coin, licensed under CC BY-SA 2.5.

An adult io moth, ready to take flight and find a mate. Photo by Patrick Coin, licensed under CC BY-SA 2.5.

Not bad, right? Sadly, for all its showy appearance, io moths don’t have mouthparts and cannot feed as adults. A lucky moth dies when its energy reserves run out after about a week, if it can manage to avoid being snapped up by bats, spiders, and other hunters.

This has its benefits — a moth with no appetite can spend its time and energy mating and laying eggs as much as possible. It also has consequences — the caterpillars, to prepare for the most important week of their lives, have to eat a lot. Within a few weeks of devouring as much greenery as physically possible, an io caterpillar can go from being a half-inch-long worm to a nearly three-inch-long monstrosity, brilliant green with red and white racing stripes:

An io moth caterpillar, almost ready to spin a coccoon. Photo by Tim Lethbridge, licensed under CC BY-ND-NC 1.0.

An io moth caterpillar, almost ready to spin a coccoon. Photo by Tim Lethbridge, licensed under CC BY-ND-NC 1.0.

See the spiky, poisonous-looking tufts growing out of the caterpillar’s back and sides? Io caterpillars are indeed capable, and more than willing, to deliver a painful sting. If you brush up against these spines, the tips will break off and start to inject venom. It’s not nice, but not much worse than an encounter with stinging nettle plants which, incidentally, uses many of the same toxins. The strategy is shared by other hemileucine caterpillars, among which are some of the largest and most conspicuous moths in North America.

Southern Brazil has its own hemileucines, including members of the genus LonomiaLonomia moths are large and attractive, if perhaps a bit less flashy than their northern brethren:

An adult Lonomia moth from Brazil. Photo by Benjamint, licensed under GFDL 1.2.

An adult Lonomia moth from Brazil. Photo by Benjamint, licensed under GFDL 1.2.

Their caterpillars, too, are less conspicuous, which is why they sometimes wind up stinging people. A single sting contains only a miniscule amount of venom — not nearly enough to do any real harm. The problem comes from the fact that hemileucine caterpillars tend to feed in groups. If a person accidentally brushes up against 20 or more Lonomia at the same time, the result can be severe.

Unlike the io caterpillar, Lonomia has venom designed to do more than just irritate the skin. As soon as it enters the bloodstream, anticoagulants work to prevent the blood from clotting, while other proteins punch holes in the victim’s blood vessels. The result is violent internal bleeding. In the worst cases, death is usually the result of internal bleeding in the brain (Pinto et al. 2010).

Each of these spines contains a tiny amount of venom. Photo from Centro de Informações Toxicológicas de Santa Catarina, in public domain.

Each of these spines contains a tiny amount of venom. Photo from O Centro de Informações Toxicológicas de Santa Catarina, in public domain.

Over the last few decades, cases in southern Brazil have been on the rise, and scientists at the Butantan Institute in São Paulo have been studying the molecular aspects of Lonomia venom. The most important result is that Brazilian hospitals now have access to an antivenom that quickly halts the venom’s action.

To North Americans a venomous caterpillar, even a deadly one, might seem like an esoteric problem. Yet in parts of southern Brazil, the caterpillar causes more medical emergencies than any snake, spider, or scorpion (Pinto et al. 2010). The Brazilian Ministry of Health estimated that in 2008, for every 100,000 people in the caterpillar’s range, there were eight stings. Meanwhile, incidents have become more common as rain forest has been replaced by fruit tree plantations, which happen to provide ideal habitat for Lonomia, and the stage for deadly encounters.

A cluster of Lonomia obliqua caterpillars. Photo from Photo from O Centro de Informações Toxicológicas de Santa Catarina, in public domain.

A cluster of Lonomia obliqua caterpillars. Photo from O Centro de Informações Toxicológicas de Santa Catarina, in public domain.

Cited:

Pinto A.F.M., M. Bergerm J. Reck, R.M.S. Terra, and J.A. Guimaraes. 2010. Lonomia obliqua venom: In vivo effects and molecular aspects associated with the hemorrhagic syndrome. Toxicon 56(7): 1103-1112.

Death by Disintegrin

by Joseph DeSisto

Disintegrins. Definitely the coolest-sounding proteins, manufactured by some of the coolest animals, the vipers.

Snake venom contains thousands of different proteins, making it one of the most complex substances in the natural world. Not all of these proteins are toxic, but those that are belong to four major categories, depending on their effects.

Neurotoxins act on your nervous system, which can make for a bad time. Your nerve cells are needed to control muscle movement, and since muscle movement allows you to breath, neurotoxic venom can cause death by paralyzing your ability to do so. Neurotoxins are found in cobras, sea snakes, and their relatives, but seldom in vipers.

Cytotoxins are the good old-fashioned cell-killers, found in many snake venoms. If you get bitten by a venomous snake, these are the proteins that start killing the tissue around the bite. If enough tissue dies on a limb, amputation might be necessary. More often, cytotoxins just make venomous snake bites really, really painful.

A Russell's viper (Daboia russelli) from Bangalore, one of the deadliest vipers in the world. Photo by Sandilya Theuerkauf, licensed under CC BY-SA 2.5.

A Russell’s viper (Daboia russelli) from Bangalore, one of the deadliest vipers in the world. Photo by Sandilya Theuerkauf, licensed under CC BY-SA 2.5.

Hemotoxins are more a viper’s purview, and act on the cardiovascular system. They can destroy red blood cells, prevent the blood from clotting, or just destroy cardiovascular tissue. While neurotoxins are relatively fast-acting, death by hemotoxin is slow. When a mouse or other prey animal is bitten by a viper, it typically runs away for some distance before it succumbs to shock. This presents vipers with a problem — how to track down prey after it has gone off to die? But before we answer that question …

The fourth category, proteases, are proteins that specialize in breaking down other proteins, and viper venom is positively loaded with them. Disintegrins are just one class of proteases, but have many functions. Their primary purpose is to break apart integrin, the stuff animals use to keep their cells stuck together. Disintegrins can also prevent blood from clotting, and have been used in medical research (McLane et al. 2004). Finally, two special disintegrins have a third purpose: they serve as tracking signals that can help the predator find its poisoned prey.

The western diamondback rattlesnake (Crotalus atrox). Photo by Holger Krisp, licensed under CC BY 3.0.

The western diamondback rattlesnake (Crotalus atrox). Photo by Holger Krisp, licensed under CC BY 3.0.

It was only a decade ago that Parker and Kardong (2005) first demonstrated, through a set of experiments, that rattlesnakes (a subfamily of vipers) use airborne scents to relocate their prey after injecting venom. Prior to that, it was thought that rattlesnakes followed a scent trail on the ground. Although experiments had since suggested that rattlesnakes are attracted to prey containing venom, it was unclear just how venom was being used to track prey.

Modern chemistry was the key. Saviola and colleagues (2013) extracted venom from diamondback rattlesnakes, then separated it into some of its major chemical components. With the venom divided, the authors injected each mouse with a different component, then offered these mice to the snakes, as well as mice that had been injected with un-divided venom. Snakes were by far the most responsive to mice that had either been injected with whole venom or with two proteins: crotatroxins 1 and 2, both of which are disintegrins.

So, rattlesnakes don’t merely “smell their own venom” — they smell to a particular pair of compounds, without which they would be unable to find prey after it had been bitten. Vipers very well might not have evolved the bodies, venoms, and life strategies we see today if it had not been for this tiny but crucial adaptation.

The western diamondback rattlesnake (Crotalus atrox) Photo by Clinton & Charles Robertson, licensed under CC BY 2.0.

The western diamondback rattlesnake (Crotalus atrox). Photo by Clinton & Charles Robertson, licensed under CC BY 2.0.

Cited:

McLane M.A., E.E. Sanchez, A. Wong, C. Paquette-Straub, J.C. Perez. 2004. Disintegrins. Current Drug Targets: Cardiovascular and Haematological Disorders 4(4): 327-355.

Parker M.R. and K.V. Kardong. 2005. Rattlesnakes can use airborne cues during post-strike prey relocation. In Mason R.T. et al. (Eds.), Chemical Signals in Vertebrates 10 (397-402). Springer.

Saviola A.J., D. Chiszar, C. Busch, and S.P. Mackessy. 2013. Molecular basis for prey relocation in viperid snakes. BMC Biology 11(20) doi: 10.1186/1741-7007-11-20

Spiders Only Love Once

by Joseph DeSisto

In one of many vain attempts to show me that birds and mammals are far superior to invertebrates, a good friend once reminded me that swans only love once, in reference to some pop song or another. I reminded her that many spiders, too, only love once — for very different reasons.

Being a spider with parental care sounds like a good deal. Mother spiders of the Mediterranean lined spider (Stegodyphus lineatus) raise their young in silken nests and guard them as they grow, feeding them and reducing the likelihood that they will be found by predators. This is all well and good, but beneath it is a story, one of murder and suicide, sex and deceit, loyalty and sacrifice.

A mother spider, Stegodyphus lineatus. Photo by Joaquin Portela.

A mother spider, Stegodyphus lineatus. Photo by Joaquin Portela.

Romance

By the time a female lined spider has reached adulthood, her web is well-established (Maklakov et al. 2005). Rather than build a single, simple web like many other spiders do, lined spiders builds a shelter out of silk on a bush and then constructs many tangled webs, all radiating from the shelter. This way, she can capture prey from multiple locations, and when her young emerge, they have plenty of webs from which to harvest prey.

Males, on the other hand, spend most of their time wandering around looking for females. When a male finds one, he approaches with caution. She is much bigger than him, and may attack him if she is not in the mood for company. If, for example, she already has a clutch of eggs, or if she is not old enough to mate, or if she is just feeling hungry, he might be out of luck.

If, however, she is receptive, the male will mate with her and then stay for a few days, to prevent any other males from approaching. When he (or she) decides it is time to go, he rushes out to avoid being attacked, and then continues wandering about, in case he should find another female. This hardly ever happens. Almost invariably, male spiders only love once.

Murder

When she lays her eggs, the female spider wraps them in a silken ball called an “egg sac.” This she guards for up to two weeks until the young hatch. Although they are guarded by a ferocious mother spider, the eggs are very vulnerable. Ants are common predators and, in their armies of hundreds, can easily overwhelm a single spider.

A Stegodyphus web from South Africa (note: not S. lineatus). Photo by Harvey Barrison.

A Stegodyphus web from South Africa (note: not S. lineatus). Photo by Harvey Barrison.

Perhaps the greatest threat, though, is more familiar: male spiders. Just as male lions and polar bears kill the young of rivals, male lined spiders frequently steal and destroy the egg sacs of females (Schneider and Lubin 1997). Why do they do this? First, stealing a female’s egg sac removes competition — his offspring will not have to compete with the product of another male’s successful mating. Second, once a female loses her eggs she becomes able to mate again, allowing the infanticidal male to replace her former partner as the father of her progeny.

This seems cruel, but male spiders are dealt a hard lot in life. While a female may encounter many males in her lifetime, and indeed will mate with many of them (Maklakov et al. 2005). Her ability to do so, however, is because of her lifestyle as a sedentary, shelter-dwelling female. Males, on the other hand, suffer a high mortality due to their wandering habits, and many males will only encounter a single female in a lifetime. So, when he encounters her, if she already has an egg sac, he will do whatever it takes to make her receptive again, even if it means killing the young she already has.

Sacrifice

The female has ways of preventing this from happening. She can lay her eggs later in the season, when all the males have either mated or died (Schneider 1999). Or, she can simply chase away/beat up/kill any male that tries to bother her after she lays eggs.

Either way, if her eggs are fortunate enough to survive, she can look forward to caring for the young for a few weeks, catching food for them from the web and mashing it up so their adorable little mouthparts don’t get damaged. During this time, the young are completely dependent on their mother, but as they get older, they venture out onto the web themselves to harvest their own prey.

The Negev Desert in Israel, a location where some of the research on the life of Stegodyphus has taken place. These are arid and semi-arid specialist spiders, found in dry habitats surrounding the Mediterranean. Photo by Andrew Shiva.

The Negev Desert in Israel, an area where some of the research on the life of Stegodyphus has taken place. These are arid and semi-arid specialist spiders, found in dry habitats surrounding the Mediterranean. Photo by Andrew Shiva.

Meanwhile, the mother undergoes major changes. Her digestive organs begin to degrade, and ultimately disintegrate as she stops feeding herself (Salomon et al. 2015). By the time her young are ready to leave the nest, her internal organs have begun to liquefy. It is time for one last gift to her offspring: her body. The spiderlings, which she protected from infanticidal males, carefully incubated as eggs, and offered her own food as tiny spiders, now eat their mother as their last meal before leaving the web and heading out into the world (Salomon et al. 2005).

Why does she do this? Believe it or not, it is to her genetic advantage to give her life to ensure her progeny’s survival. The world is a harsh place for spiders, and not only are her chances of successfully raising a second clutch next to nothing, but each of her spiderlings has at best a meager chance of survival. Offering her own body gives them the best possible head start in life, and ensures that at least a few of them will be able to grow, mate, and raise young themselves.

Cited:

Maklakov, A.A., T. Bilde, and Y. Lubin. 2005. Sexual conflict in the wild: Elevated mating rate reduces female lifetime reproductive success. The American Naturalist 165(S5): S38-S45.

Salomon, M., E.D. Aflalo, M. Coll, and Y. Lubin. 2015. Dramatic histological changes preceding suicidal maternal care in the subsocial spider Stegodyphus lineatus (Araneae: Eresidae). Journal of Arachnology 43(1): 77-85.

Salomon, M., J. Schneider, and Y. Lubin. 2005. Maternal investment in a spider with suicidal maternal care, Stegodyphus lineatus (Araneae, Eresidae). Oikos 109(3): 614-622.

Schneider, J.M. 1999. Delayed oviposition: A female strategy to counter infanticide by males? Behavioral Ecology 10(5): 567-571.

Schneider, J.M. and Y. Lubin. 1997. Infanticide by males in a spider with suicidal maternal care, Stegodyphus lineatus (Eresidae). Animal Behavior 54: 305-312.

The Woodlouse Spiders

by Joseph DeSisto

In my last post, I talked about centipedes with unusually long, narrow fangs, and how in the woodlouse spiders of the genus Dysdera, such strange devices are an adaptation for hunting woodlice. These spiders, however, deserve more than a mention in an article about another animal, so let’s talk about woodlouse spiders, and why they are so cool.

Woodlouse spiders are weird. They look weird, they act weird, and naturally I think they’re great. Here in North America we only have one species of Dysdera, and that’s D. crocata. This species is actually introduced from Eurasia, where it lives with around 200 other members of the genus. These spiders are relatively large, mostly hairless, and do not spin webs. Dysdera are also quite handsome as far as spiders go, cloaked in red, orange, and pale brown.

Dysdera crocata, the only woodlouse spider found in North America. This one is just over a centimeter in length, not including the legs. Photo by Tom Murray.

Dysdera crocata, the only woodlouse spider found in North America. This one is just over a centimeter in length, not including the legs. Photo by Tom Murray.

The biggest reason these spiders look so strange has to do with their fangs. A spider’s fangs are called chelicerae, and are modified mouthparts, in contrast to a centipedes “fangs” which are modified legs. Fangs can come in all shapes and sizes, but the woodlouse spider’s are probably some of the biggest, relative to its body size, of any spider. The fangs are enormous, and indicate a specialized hunting strategy: woodlouse spiders, as their name suggests, are specialist predators of woodlice or pill bugs.

Or are they? The question, as it turns out, is more complex than you might expect. Pollard et al. (1995) experimented by offering D. crocata spiders different sorts of prey: two types of woodlouse, but also flies, beetle larvae, crickets, and other many-legged morsels. The result: the spiders did not prefer woodlice. So what’s going on here?

A woodlouse spider's fangs, up close. Photo by Tom Murray.

A woodlouse spider’s fangs, up close. These are adapted for killing heavily armored woodlice. Photo by Tom Murray.

More than a decade later, Řezác and Pekár (2007) did pretty much the same experiment, and again saw that the spiders didn’t prefer woodlice over the alternative, in this case fruit flies. In fact, their spiders actually ate more flies than woodlice! But they also conducted a second experiment in which they raised young Dysdera on diets of either woodlice, flies, or a mix of the two.

When the spiders weren’t allowed to choose their food, those that ate woodlice developed significantly faster than those that ate only flies. It seems that, although woodlouse spiders are adapted to be woodlouse specialists, certain circumstances, including captivity, can cause them to change their preferences. Perhaps in the captive setting, flies are just easier prey than woodlice.

Woodlice, the primary prey of Dysdera spiders ... most of the time. Probably. Photo by Tom Murray.

Woodlice, the primary prey of Dysdera spiders … most of the time. Probably. Photo by Tom Murray.

It is worth pointing out that Řezác and Pekár conducted their experiment with a different but closely related species of spider (Dysdera hungarica) than Pollard et al. This may seem trivial, but in fact there is a lot of variation in feeding strategies among the woodlouse spiders. Although all appear to be specialized to some degree, the way in which their enormous fangs help them dispatch their armored prey varies quite a lot between species.

For example, Řezác et al. (2008) found that Dysdera spiders with concave chelicerae use them to stab woodlice from beneath, whereas others have flattened fangs they can slide between the prey’s plates of armor. Not only do different species have different methods of killing woodlice, some species with relatively “normal-looking” fangs refuse to attack woodlice in captivity.

So, not to worry if you were hoping to study woodlouse spiders: there is plenty of work still to be done.

Cited

Pollard, S.D., R.R. Jackson, A. Van Olphen, and M.W. Robertson. 1995. Does Dysdera crocata (Araneae Dysderidae) prefer woodlice as prey? Ethology Ecology & Evolution 7(3): 271-275.

Řezác, M. and S. Pekár. 2007. Evidence for woodlice-specialization in Dysdera spiders: behavioral versus developmental approaches. Physiological Entomology 32: 367-371.

Řezác, M., S. Pekár, and Y. Lubin. 2008. How oniscophagous spiders overcome woodlouse armour. Journal of Zoology 275: 64-71.

Samara’s Centipedes

by Joseph DeSisto

Although I am interested in all sorts of creatures, I specialize in centipedes, and after having several conversations to this effect, there are a few things I would like to clear up. No, I haven’t seen The Human Centipede. No, I don’t want to. And no, I don’t want to listen to you describe the plot in excruciating (or really any) detail.

800px-Scolopendra_polymorpha_1

Scolopendra polymorpha. Photo by Matt Reinbold.

That said, I do enjoy well-made, less grotesque horror movies. The other night I watched The Ring, directed by Gore Verbinski (2002), and I’m pleased to report it’s my new favorite movie featuring a centipede.

Admittedly, the centipede’s two appearances are brief, but to be fair, centipedes don’t make for very complex characters. Near the start of the movie, the protagonist (played by Naomi Watts) watches a tape with a number of horrifying images, including a short clip of a centipede emerging from beneath a table. The tape is in black-and-white, but the size of the centipede places it in the family Scolopendridae, and the striking banded pattern suggests it almost certainly belongs to the species Scolopendra polymorpha.

If any centipede genus deserves a role in a horror classic, it’s Scolopendra, and not just for a Latin name which, let’s be honest, is pretty bad-ass. S. polymorpha in particular is found in xeric habitats through much of the western United States and northern Mexico. Beautifully adorned in bands of black, red-orange, and yellow, this 6-inch-long bruiser is one of the top predators in the dark, damp underground of North America’s deserts. Their main prey are other arthropods, which they kill with a powerful neurotoxic venom.

Across the world’s tropics and subtropics, giant centipedes in the genus Scolopendra prey on pretty much everything they can fit between their poison injecting front claws. This can include all sorts of invertebrates, as well as vertebrates, including lizards, snakes, frogs, and mice. In Venezuela, S. gigantea, a 10-inch-long behemoth, has been recorded hanging upside-down in caves and, snake-style, snatching unfortunate bats out of the air (Molinari et al. 2005). Despite being formidable, they are also prey themselves. In the southwestern U.S. desert, S. polymorpha has been recorded as prey for the much smaller but highly venomous scorpion, Centruroides sculpturatus (Graham and Webber 2013). Scorpions are hugely important predators in deserts, and they may be one of polymorpha‘s main predators.

Although a bite from a giant centipede can be extremely painful, their venom may have practical applications, especially in medicine and medical research. A study by Yang et al. (2013) demonstrated that a particular protein found in the venom of the Chinese Scolopendra subspinipes mutilans inhibited pain in mice. The protein apparently uses the same molecular pathway as morphine, but with greater efficiency.

Scolopendra subspinipes mutilans, from China. Photo by Yasunori Koide.

Scolopendra subspinipes mutilans, from China. Photo by Yasunori Koide.

As The Ring progresses, scenes from the tape are reflected in the life of Watts’ character. Towards the end, as she is shuffling through an old box, a large centipede emerges and startles her before racing off into the darkness, not to be seen again. This centipede was another scolopendrid, but not polymorpha. The color pattern wasn’t unique enough to make a positive identification. In other words, I was partially covering my eyes when the centipede emerged.

Scolopendra heros. Photo by Aaron Goodwin.

Scolopendra heros, another scolopendrid from North America’s deserts. Photo by Aaron Goodwin.

A lot of biologists get annoyed when their favorite animals are used in horror movies, especially when the movie either completely misrepresents the animal in question or is just really bad. But I have to say, I don’t really mind when giant centipedes are used to increase the scare factor of a scene, especially in a movie as good as The Ring. Frankly, the reasons people like to put them in movies are all the same reasons I find them worth studying. Centipedes are pretty scary, at least the giant ones. They’re the perfect combination of long, slithery snake-ness with many-legged, venom-injecting spider-ness. But they are also mysterious, fascinating, and awe-inspiring creatures, and the world would be a poorer place without them. They are beautiful nightmares.

Cited:

Molinari, J., E.E. Gutiérrez, A.A. De Ascenção, J.M. Nassar, A. Arends, R.J. Marquez. 2005. Predation by giant centipedes, Scolopendra gigantea, on three species of bats in a Venezuelan cave. Caribbean Journal of Science 41(2): 340-6.

Webber, M.M., and M.R. Graham. 2013. An Arizona bark scorpion (Centruroides sculpturatus) found consuming a venomous prey item nearly twice its length. Western North American Naturalist 73(4): 530-2.

Yang, S., Y. Xiao, D. Kang, J. Liu, Y. Li, E.A.B. Undheim, J.K. Klint, M. Rong, R. Lai, and G.F. King. 2013. Discovery of a selective Nav1.7 inhibitor from centipede venom with analgesic efficacy exceeding morphine in rodent pain models. Proceedings of the National Academy of Sciences 110(43): 17534-9.