Tag Archives: predator

Arthropods vs. Cane Toads

Cane toads are toxic because their bodies are loaded with cardiac glycosides, deadly toxins that can stop a predator’s heart. Because the toads are non-native in Australia, the native Australian carnivores aren’t adapted to dealing with them. For some, this is very bad news: freshwater crocodiles, monitor lizards, and pythons have all experienced population declines since the introduction of cane toads in 1985 (Smith and Phillips 2006).

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A cane toad. Photo by Sam Fraser-Smith, licensed under CC BY 4.0.

Not all is lost, however. It turns out that cardiac glycosides are only toxic to a very narrow group of animals: vertebrates. Predatory insects, arachnids, and other invertebrates have no trouble at all with the poison. Furthermore, a study published earlier this year (Cabrera-Guzmán et al. 2015) revealed that many are more than capable of tackling amphibian prey.

Cane toads start their lives as tadpoles, small and innocent, but plenty toxic enough to kill a hungry frog or fish. In Australia, some of their top predators are giant water bugs and water scorpions. Both are insects (not scorpions) that use tube-like mouthparts to inject acid and digestive enzymes into their prey, dissolving them from the inside out. When the tadpole’s innards are sufficiently liquefied, the insects slurp them up like an amphibian milkshake.

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A water scorpion lying in wait for prey. Photo by N. Sloth, licensed under CC BY-NC 3.0.

A young dragonfly's mouthparts. Photo by Siga, licensed under CC BY-SA 3.0.

A young dragonfly’s mouthparts. Photo by Siga, licensed under CC BY-SA 3.0.

Dragonfly larvae are also aquatic and predatory, but instead of using acid, they have extendable mouthparts. These are built like the robotic arm on an automatic garbage truck, but less cumbersome and more of a surgical, spring-loaded instrument of death. Most dragonfly larvae eat other insects, like mosquito larvae, but the largest species can easily overpower a small fish or tadpole.

Diving beetles join in the fun. Their mouthparts are less exciting, more like a typical beetle’s with sharp, biting mandibles. What makes them special is speed: their bodies are constructed like those of sea turtles. Like sea turtles, diving beetles are hard-shelled, streamlined, and aquadynamic. Unlike sea turtles, diving beetles use this form to swim after tadpoles that aren’t quite fast enough to escape.

A diving beetle, waiting for tadpoles to swim by. Photo by N. Sloth, licensed under CC BY-NC 3.0.

A diving beetle, waiting for tadpoles to swim by. Photo by N. Sloth, licensed under CC BY-NC 3.0.

A diving beetle larva with tadpole prey. Photo by Gilles San Martin, licensed under CC BY-SA 2.0.

A diving beetle larva with tadpole prey. Photo by Gilles San Martin, licensed under CC BY-SA 2.0.

Diving beetle larvae are just as fierce, and they too have been observed feeding on cane toad tadpoles. Unlike their parents, larvae are long-bodied, with curved, needle-like jaws which they use to inject digestive enzymes into their prey (like the water bugs).

Any cane toad tadpoles that survive this massacre can metamorphose into toadlets, but until they reach their adult size (4-6 inches) they are still at the mercy of their invertebrate predators.

Experiments and observations in the field (Cabrera-Guzmán et al. 2015) have revealed that crayfish are efficient predators of eggs, tadpoles, toadlets, and even adult toads. Australia is home to 151 species of crayfish, including several of the largest species on earth. The spiny crayfish (Euastacus) in particular, some of which can grow to more than a foot in length, prey not only on toadlets but also on full-sized, adult cane toads.

A Lamington blue spiny crayfish (Euastacus sulcatus). Photo by Tatters, licensed under CC BY-SA 3.0.

A Lamington blue spiny crayfish (Euastacus sulcatus). Photo by Tatters, licensed under CC BY-SA 3.0.

There are, believe it or not, spiders that specialize in running out over the surface of the water to snatch aquatic insects, tadpoles, and small fish. They are the fishing spiders (large ones are sometimes called dock spiders). Experiments have shown that when fishing spiders inhabit a pond, up to 1 in every 4 tadpoles ultimately becomes spider food (Cabrera-Guzmán et al. 2015).

A fishing spider, ready for a meal. Photo by Patrick Coin, licensed under CC BY-NC-SA 2.0.

A fishing spider, ready for a meal. Photo by Patrick Coin, licensed under CC BY-NC-SA 2.0.

Finally, ants. In the cane toad’s native range of tropical Latin America, meat ants are a major predator. When a toad is attacked, it often stays still, relying on poison for protection. Ants take advantage of this strategy, swarming over the toad’s body and stinging it to death with poisons of their own. Meat ants (Iridomyrmex) and their relatives also live in Australia, and they have been seen dragging the dismembered remains of cane toads back to their nests.

Meat ants taking down a cicada nymph. Photo by jjron, licensed under GFDL 1.2.

Meat ants taking down a cicada nymph. Photo by jjron, licensed under GFDL 1.2.

I’m sorry to say giant centipedes did not make the list of cane toad predators in Australia, but I should mention that the Caribbean giant centipede (Scolopendra alternans) has been observed to prey on native cane toads (Carpenter and Gillingham 1984).

Whether bird-eating spiders, bat-snatching centipedes, or tadpole-chasing water bugs, invertebrates that prey on vertebrates are always fascinating. It’s more common than you might think! I’ll conclude by mentioning Epomis, an unusual genus of ground beetles. Both the beetle larvae and adults are specialist amphibian-eaters, and tackle frogs and toads many times their own size.

Epomis beetles attacking various European amphibians. Photos from Wizen and Gasith (2011), licensed under CC BY 3.0.

Epomis beetles attacking various European amphibians. Photos from Wizen and Gasith (2011), licensed under CC BY 3.0.

I won’t say any more, since Epomis expert Gil Wizen has already written a fantastic blog post about these beetles, complete with videos of predation in action! I encourage you to check it out here.

Cited:

Cabrera-Guzman E., M.R. Crossland, and R. Shine. 2015. Invasive cane toads as prey for native arthropod predators in tropical Australia. Herpetological Monographs 29(1): 28-39.

Carpenter C.C. and J.C. Gillingham. 1984. Giant centipede (Scolopendra alternans) attacks marine toad (Bufo marinus). Caribbean Journal of Science 20: 71-72.

Smith J.G. and B.L. Phillips. 2006. Toxic tucker: the potential impact of cane toads on Australian reptiles. Pacific Conservation Biology 12(1): 40-49.

Wizen G. and A. Gasith. 2011. Predation of amphibians by carabid beetles of the genus Epomis found in the central coastal plain of Israel. ZooKeys 100: 181-191.

Why Scorpion Venom is So Complex

by Joseph DeSisto

Scorpion venom, like many animal venoms, is incredible complex. It is made up of hundreds of different toxins and other proteins, each with a specific function, all mixed together in a lethal cocktail. Why do scorpions need so many different toxins? Last week, scientists at the Chinese Academy of Sciences published the results of their attempt to answer this question (Zhang et al. 2015).

They began by studying a particular class of proteins found in scorpion venom, which work by attacking the sodium ion-channel proteins in their victims.

The stripe-tailed scorpion, Vaejovis spinigerus, ready for action.. Photo by Joseph DeSisto.

The stripe-tailed scorpion, Vaejovis spinigerus, ready for action. Photo by Joseph DeSisto.

Sodium ion-channels help regulate the amount of sodium inside animal cells, which is vital for cells to function properly. In nerve cells, they are even more important: the change in sodium concentration inside and outside the cell is what transmits electric signals.

Toxins that inhibit sodium channels prevent the nervous system from working, which leads to death if the victim is small (like an insect). Scorpions have toxins called sodium-channel toxins to do exactly that. The puzzle is, scorpions have many different genes that produce sodium-channel toxins, each of which has a slightly different structure.

All proteins are essentially strings that are wound, twisted, and tied into a specific structure. The structure of a protein is critical to its function, since proteins need to have certain shapes in order to interact with each other like a lock and key. All sodium-channel toxins have a portion designated as the “interactive region” — the key — which attaches to a series of loops on the prey’s sodium ion-channel (the lock). If the key fits and the connection is successful, the prey’s ion-channel can no longer function.

A mother stripe-tailed scorpion, carrying young. Photo by Joseph DeSisto.

A mother stripe-tailed scorpion, carrying young. Photo by Joseph DeSisto.

Zhang and his colleagues studied the genome of their scorpion, a desert-dwelling East Asian species known as the Chinese golden scorpion (Mesobuthus martensii). They found no less than 29 different genes coding for sodium channel toxins.

There was a time, perhaps hundreds of millions of years ago, when scorpions only had one gene for sodium-channel toxins. Eventually that gene was duplicated, and thereafter the scorpion genome had multiple copies of the same toxin-producing gene. Since then, each copy of the gene has continued to mutate and evolve in its own direction. Now each toxin, despite having the same basic structure, is just a little bit different from the rest.

As it happens, the genes for sodium ion-channels in a scorpion’s prey also exist in multiple copies, each with minor variations. Zhang and colleagues hypothesized that scorpions need so many varieties of toxins because each toxin can only interact with a specific variety of ion-channel. In other words, scorpion venom needs lots of different keys because the prey have so many different locks.

To test this, the scientists examined the different toxin-gene copies to better understand how they had evolved. Sure enough, the “interactive region,” the key, of each toxin had mutated and evolved much more quickly than the “body” of the toxin. This provided strong evidence that natural selection has caused scorpion venom to evolve different types of toxins to keep up with the ever-evolving ion-channels in their prey.

Scorpions are incredible animals for so many reasons. They have been around for more than 400 million years — as long as there have been insects to hunt on land, scorpions have been there to hunt them. They are amazing and diverse in form, lifestyle, and hunting strategy. How fitting that they should be just as amazing on the molecular level.

Cited:

Zhang S., B. Gao, and S. Zhu. Target-driven evolution of scorpion toxins. Nature Scientific Reports 5:14973 doi: 10.1038/srep14973

The Green Lynx: Friend or Foe?

by Joseph DeSisto

I’m currently in Arizona, and don’t have much time for writing, but I’m just seeing too many cool things not to show you one of them. There are some amazing arachnids in the Southwest: so far I’ve seen tarantulas, scorpions, sun spiders, and black widows, all of which will appear on this site in some fashion. As a teaser, here’s a green lynx spider, common in much of the southern United States:

The green lynx spider (Peucetia viridans), with a yummy burnet moth. Lynx spiders are extremely versatile predators -- this moth is highly toxic, but the spider doesn't seem to mind. Photo by Joseph DeSisto.

The green lynx spider (Peucetia viridans), with a yummy burnet moth. Lynx spiders are extremely versatile predators. Photo by Joseph DeSisto.

The prey above is a burnet moth in the family Zygaenidae. Its colors are a warning sign that this moth is extremely toxic, loaded with hydrogen cyanide, but this spider doesn’t seem to mind.

Most spiders fall into one of two categories based on hunting strategy: ambush predators (including web-builders) and wandering hunters. Lynx spiders are both. The one above waited patiently before grabbing a passing moth. Tomorrow, though, it might just as easily stride over the foliage, searching for less active preys such as caterpillars.

Aside from being an efficient hunter, green lynx spiders are very adaptable and do well in gardens and farms. Because they can be extremely abundant, biologists have studied their ecology to determine whether they might be useful to farmers. Whitcomb et al. (1963) recorded them as important predators of several important crop pests, notably the corn earworm, cotton leafworm, and cabbage looper, all three both as adult moths and as caterpillars.

The corn earworm, an important pest caterpillar in American corn fields, and prey for lynx spiders. Photo by Cydny Sims Parr, licensed under CC BY-SA 2.0.

The corn earworm (Helicoverpa zea), an important pest caterpillar in American corn fields, and prey for lynx spiders. Photo by Cydny Sims Parr, licensed under CC BY-SA 2.0.

The trouble is, lynx spiders don’t really care if the insects they eat are pests, and some of their favorite prey are beneficial insects. They are more than happy to eat wasps, which themselves are important caterpillar predators. The honey bee, an important pollinator, is one of their favorites (Whitcomb et al. 1966).

To determine just how useful lynx spiders actually were, Randall (1982) conducted a survey of prey items captured by lynx spiders throughout Florida. He then rated the spiders’ victims by importance to farmers: an insect cadaver could be either extremely harmful (e.g., cotton leaf worm), extremely beneficial (e.g., honey bee) or anywhere in between.

The green lynx spider. Photo by Joseph DeSisto.

The green lynx spider, Peucetia viridans. Photo by Joseph DeSisto.

A total of 66 prey items were recorded, and in the end, data pointed to these spiders eating as many beneficial insects as harmful ones. So the green lynx spider might not be especially important to farmers. Or, more accurately, the green lynx is neither beneficial nor harmful. It is simply a spider trying to make a living however it can, irrespective of human interests.

Cited:

Randall J.B. 1982. Prey records of the green lynx spider, Peucetia viridans (Hentz) (Araneae, Oxyopidae). Journal of Arachnology 10: 19-22.

Whitcomb W.H., H. Exline, and R.C. Hunter. 1963. Spiders of the Arkansas cotton field. Annals of the Entomological Society of America 56(5): 653-660.

Whitcomb W.H., M. Hite, and R. Eason. 1966. Life history of the green lynx spider, Peucetia viridans (Araneida: Oxyopidae). Journal of the Kansas Entomological Society 39: 259-267.

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

Mystery Maggots from South Carolina

by Joseph DeSisto

While tearing apart logs in Sumter National Forest, I came across this little spectacle:

Mystery fly larvae, found under a log in Sumter National Forest, South Carolina. Photo by Joseph DeSisto.

Mystery fly larvae, found under a log in Sumter National Forest, South Carolina. Photo by Joseph DeSisto.

The stuff that looks like a fried egg is a fungus, growing on the rotting wood. The worm-like animals are insect larvae, and I found them in a cluster with 20 or so others, all squelching about over the fungus.

The lack of legs and “maggot-like” appearance mark these as larvae that will one day become flies. The problem is, the fly order Diptera contains around 120,000 known species, and many undescribed. Since they were found on a fungus, I felt comfortable placing them in the Sciarioidea or “gnats,” which includes a lot of flies with fungus-feeding larvae. That’s a little more specific, but with seven families and nearly 12,000 described species, I still had a long way to go.

The two largest families of fungus-feeders in this group are the fungus gnats Mycetophilidae and Sciaridae, with 3,000 and 1,700 known species, respectively. Many more species have yet to be discovered, especially in the tropics which is pretty much a black box as far as fungus gnat diversity is concerned.

Below is an example of an adult fungus gnat. Most of these insects are less than a centimeter in length as adults, although the maggots can be a bit larger.

A typical fungus gnat, Tarnania fenestralis. Photo by Jostein Kjaerandsen, licensed under CC BY-NC 3.0.

A typical fungus gnat, Tarnania fenestralis. Photo by Jostein Kjaerandsen, licensed under CC BY-NC 3.0.

The name “fungus gnat” makes these creatures sound pretty wimpy. It’s true, the vast majority spend most of their lives as larvae burrowing into mushrooms, until they emerge as minute flies that live around a week. In general, people who don’t specialize in fungus gnat research regard them as pretty boring, at least compared to some of the larger, more spectacular flies out there.

Let’s take another look at our mystery maggots:

The same maggots from South Carolina. Note the shiny, sticky stuff coating the fungus -- that's a mixture of silk and glue produced by the larvae. Photo by Joseph DeSisto

The same maggots from South Carolina. Note the shiny, sticky stuff coating the fungus — that’s a mixture of silk and glue produced by the larvae. Photo by Joseph DeSisto

See the shiny, gluey stuff covering some of the fungus? That’s silk, and it’s hygroscopic which means it harvests moisture from the air. It’s our biggest clue in figuring out where these larvae belong, because silk is used not to eat fungus, but to ensnare prey. These innocent little fungus gnats are actually the maggot equivalents of spiders, ambush predators that wait for helpless insects to become trapped in a sticky web.

Predatory fungus gnats are not mycetophilids or sciarids, but belong in their own family, Keroplatidae. This family used to be considered a subgroup of Mycetophilidae, with a modest diversity of 1,000 or so known species.

Despite relatively low species diversity, keroplatids have a wide range of lifestyles, most of which involve predation on other invertebrates. The ones I found in South Carolina are relatively benign – other species weave drops of acid into their webs, to hasten the demise of their victims. Still others attract prey by bioluminescence, and are called glow worms.

Arachnocampa larvae from a cave in New Zealand -- the hanging threads are snares ready to trap insect prey, and the droplets are bits of glue mixed with acid. Photo by Markus Nolf, licensed under CC BY-SA 3.0.

Arachnocampa larvae from a cave in New Zealand — the hanging threads are snares ready to trap insect prey, and the droplets are bits of glue mixed with acid. Photo by Markus Nolf, licensed under CC BY-SA 3.0.

The best-known glow worm is Arachnocampa luminosa, a New Zealand cave-dwelling species – you might remember it being featured in David Attenborough’s Life in the Undergrowth series. Arachnocampa larvae live in silk tubes on the ceilings of caves, and dangle silken threads with drops of acidic glue. When one gets hungry, it emits a light from its rear end, drawing insects up to the ceiling, where they become trapped. The gnat larva can then harvest and eat its prey whenever it wishes. For more about keroplatids, I recommend the introduction to the catalog by Evenhuis (2006), cited below.

When predatory fungus gnats finish their murderous childhood, they emerge as flies. At this point they look just like any other fungus gnat. Harmless and plain they may be, but boring? Ha!

A typical adult predatory fungus gnat, Orfelia lugubris. Photo by Jostein Kjaerandsen, licensed under CC BY-NC 3.0.

A typical adult predatory fungus gnat, Orfelia lugubris. Photo by Jostein Kjaerandsen, licensed under CC BY-NC 3.0.

Cited:

Evenhuis, N.L. 2006. Catalog of the Keroplatidae of the World (Insecta: Diptera). Bishop Museum Bulletin in Entomology 13: 1-178.

The Black Corsair, Terror of the Leaves

by Joseph DeSisto

The word corsair originates from the old French word corsaire, used to refer to the Barbary pirates of North Africa from the 16th to 19th centuries. The term later referred to pirates or privateers in general. Today we seldom speak of corsairs — the word has fallen out of use except among entomologists, who use it to refer to a particular subfamily of assassin bugs, the Peiratinae.

These corsairs certainly live up to their name. Just as the Barbary pirates terrorized the Mediterranean, the corsairs are just about every insects nightmare. Like all assassins they are ambush predators, waiting for the perfect moment to strike out and inject acids and enzymes into their prey. The victim is liquefied alive, and then sucked dry until only the crumpled husk of an insect remains.

Below is my personal favorite, the black corsair (Melanolestes picipes). Note the general bad-assery:

The black corsair. Photo by Ilona L., licensed under CC BY-ND-NC 1.0.

The black corsair. Photo by Ilona L., licensed under CC BY-ND-NC 1.0.

Some fun facts about black corsairs:

1) Females hiss during mating. By hiss I really mean stridulate, since they rub their mouthparts together to make the raspy sound (Moore 1961). What message this conveys to the male about his performance — positive or negative — I won’t speculate.

2) They don’t all have wings. With few exceptions (i.e., mayflies) insects don’t develop wings until they become adults. In the case of the black corsair, though, many females reach adulthood without developing wings. Since assassins are ambush predators, they don’t need to do much flying except to find mates. The males get that job.

3) They come in red. Juveniles don’t have fully developed wings, and the exposed abdomen is often reddish until adulthood. In some cases the red is never lost, and the red adults used to be considered a separate species, Melanolestes abdominalis. We now know that the two forms belong to one highly variable species (McPherson et al. 1991).

A black corsair, with the reddish abdomen retained into adulthood. Photo by Mike Quinn, TexasEnto.net, licensed under CC BY-ND-NC 1.0.

A black corsair, with the reddish abdomen retained into adulthood. Photo by Mike Quinn, TexasEnto.net, licensed under CC BY-ND-NC 1.0.

Like all assassin bugs, the black corsair belongs to the insect order Hemiptera, which consists mostly of peaceful herbivores such as stink bugs and aphids. All hemipterans have tube-shaped mouthparts and must injest their food in liquid form. But while plant-feeders have straw-shaped mouths they use to harvest sap, assassins and other predatory forms have mouths shaped like scimitars — i.e., something a pirate might use. One look at a a corsair and you know you are looking at an insect that kills other insects:

The head and prey killing device of the black corsair, Melanolestes picipes. Photo by Brigette Zacharczenko, used with permission.

The head and prey killing device of the black corsair. Photo by Brigette Zacharczenko, used with permission.

Yeah. Not something you want to pick up.

I collected the specimen above in Sumter National Forest, in South Carolina, alongside a ton of other animals with the potential to ruin my day: ticks, scorpions, really big centipedes … enough for a series, really. We’ll see.

Some housekeeping notes. First, I want to thank Brigette Zacharczenko, a PhD student at UConn. She helped me use the Macropod, a very fancy camera by Macroscopic Solutions, to take the picture above. As it happens, she too has a website/blog which features insects and especially caterpillars. You can find that here.

Second, I recently had an article published in Entomology Today, the blog/news site of the Entomological Society of America. It’s about the Migratory Dragonfly Project and how citizen scientists can get involved. You can read that here.

Cited:

McPherson, J. E., S. L. Keffer, and S. J. Taylor. 1991. Taxonomic status of Melanolestes picipes and M. abdominalis (Heteroptera: Reduviidae). Florida Entomologist 74(3): 396-403.

Moore, T. E. 1961. Audiospectrographic analysis of sounds of Hemiptera and Homoptera. Annals of the Entomological Society of America 54(2): 273-291.

Honey Bees and Pseudoscorpions: Best of Frenemies

by Joseph DeSisto

This is a pseudoscorpion. Depending on how you look at it, you might describe it as a scorpion without a stinger, or a tick with pincers. In fact, it is neither.

A pseudoscorpion, Chelifer cancroides, commonly found in houses. Photo by Christian Fischer, licensed under CC 3.0.

A pseudoscorpion, Chelifer cancroides, commonly found in houses. Photo by Christian Fischer, licensed under CC 3.0.

Pseudoscorpions are arachnids, like spiders, mites and, yes, scorpions. But unlike scorpions, pseudoscorpions are a) tiny, b) don’t have stingers and c) instead inject venom into their tiny prey through glands in their pincers (Weygoldt 1969).

To be more specific, the pseudoscorpion in the picture above is Chelifer cancroides, commonly called the house pseudoscorpion. This species is cosmopolitan — it often associates with humans and lives in buildings, where it feeds on the other assorted animals that dwell in the forgotten cracks and crevices. They are harmless, and do us a favor by keeping pests in check, although their domestic habits can lead to awkward encounters such as this one:

No children were harmed in the collection of this specimen. Photo by Joseph DeSisto.

No children were harmed in the collection of this specimen. Photo by Joseph DeSisto.

Many pseudoscorpions live on soil and leaf litter, or under the bark of rotting logs. Others have more restrictive habits: there are several species that specialize in living in honey bee hives, where they sneak about among honeycombs and bee larvae. What do they do in bee hives? Some species are beneficial. Others are decidedly not.

A grand total of 15 species of pseudoscorpions have been recorded in honey bee hives, most of them in the tropics (Gonzalez et al. 2008). Many species appear to live exclusively alongside honey bees, but hives have also been found to contain C. cancroides — remember, the one that always seems to turn up in places it shouldn’t.

At least one species, Ellingsenius handrickxi, is definitely not a bee friend — it regularly preys on the bees (Vachon 1954). Another species, Ellingsenius indicus, has been seen travelling about by clinging to the bees’ necks, which may prevent them from gathering nectar and pollen efficiently (Subbiah et al. 1957).

A honey bee hive is a dangerous place to live if you aren't a bee. Photo by Eugene Zelenko, licensed under CC 3.0.

A honey bee hive is a dangerous place to live if you aren’t a bee. Photo by Eugene Zelenko, licensed under CC 3.0.

Most pseudoscorpions don’t eat bees, but instead prey on mites, waxworms, and other invertebrates that live in honey bee hives. This can benefit the bees, since some of these squatters rob the hive of its resources: precious wax and honey. Pseudoscorpions also eat bee parasites, including Varroa mites, which can destroy honey bee colonies and devastate beekeepers.

The big question is, can we use pseudoscorpions to help control the Varroa mite? At least some species can be efficiently bred in captivity (Read et al. 2014), and unlike many other predators, pseudoscorpions are comfortable living in groups — cannibalism is rare (Weygoldt 1969).

Several New Zealand entomologists are optimistic, among them Dr. Barry Donovan. He has published several popular and technical articles touting pseudoscorpions as having potential to control Varroa. His evidence is compelling — pseudoscorpions do eat Varroa mites. Video surveillance reveals they will even remove the mites from bee larvae for an easy snack (Fagan et al. 2012).

These voracious predators can eat up to nine mites per day, and Fagan et al. (2012) estimate that a population of only 25 pseudoscorpions is enough to control Varroa mites in a typical honey bee hive. So, it seems that pseudoscorpions could be an effective way to control Varroa. Donovan and Paul (2006) even suggest modifying commercial hives to provide “breeding sites” for pseudoscorpions.

The devastating parasitic mite Varroa destructor, clinging to the head of a developing honey bee. Photo by Gilles San Martin, licensed under CC 2.0.

The devastating parasitic mite Varroa destructor, clinging to the head of a developing honey bee. Photo by Gilles San Martin, licensed under CC 2.0.

It might not be that easy. A systematic study using the pseudoscorpion Ellingsenius indicus in the Himalayas revealed that although this species may eat Varroa, it prefers to eat bee larvae, non-parasitic lice, and the remains of already-dead bees (Thapa et al. 2013). This doesn’t contradict Fagan et al.’s study showing that pseudoscorpions do eat Varroa mites — Fagan et al used a New Zealand species, not E. indicus, but an unspecified pseudoscorpion.

What the Himalayan study does tell us is that knowing all the details, including the exact species relationships, is critical. Some pseudoscorpions are beneficial and eat mites straight off the bees, but others cut out the middle-mite and just eat the bees themselves. Most species probably do both. Pseudoscorpions may prove invaluable in the war against honey bee decline, but for now, there’s a lot left to learn.

Cited:

Donovan, B.J. and F. Paul. 2006. Pseudoscorpions to the rescue? American Bee Journal 146(10): 867-869.

Fagan, L.L., W.R. Nelson, E.D. Meenken, B.G. Howlett, M.K. Walker, and B.J. Donovan. 2012. Varroa management in small bites. Journal of Applied Entomology 136: 473-475.

Gonzalez, V.H., B. Mantilla, and V. Mahnert. 2007. A new host record for Dasychernes inquilinus (Arachnida, Pseudoscorpiones, Chernetidae), with an overview of pseudoscorpion-bee relationships. Journal of Arachnology 35(3): 470-474.

Read, S., B.G. Howlett, B.J. Donovan, W.R. Nelson, and R.F. van Toor. 2014. Culturing chelifers (Pseudoscorpions) that consume Varroa mites. Journal of Applied Entomology 138: 260-266.

Subbiah, M.S., V. Mahadevan, and R. Janakiraman. 1957. A note on the occurrence of an arachnid – Ellingsenius indicus Chamberlin – infesting bee hives in South India. Indian Journal of Veterinary Science and Animal Husbandry 27: 155-156.

Thapa, R., S. Wongsiri, M.L. Lee, T. Choi. 2013. Predatory behavior of pseudoscorpions (Ellingsenius indicus) associated with Himalayan Apis cerana. Journal of Apicultural Research 52(5): 219-226.

Weygoldt, P. 1969. The Biology of Pseudoscorpions. Cambridge, Massachusetts: Harvard University Press.

Vachon, M. 1954. Remarques sur un Pseudoscorpion vivant dans les ruches d’Abeiltes au Congo Belge, Ellingsenius hendriekxi n. sp. Annales du Musbe royal du Congo Beige, N. S. Zool. 1: 284-287.

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.

Some Strange Male Centipedes

by Joseph DeSisto

Time for some centipedes! Recently I’ve been looking at a lot of centipedes in the family Lithobiidae, and in particular the striking modifications of some of the males, and I thought I’d share them here.

For those of you who don’t spend your free time studying centipedes, they are arthropods with 15 or more pairs of legs and venomous fangs. I say “fangs,” but they are technically a highly modified pair of legs, positioned beneath the head, that centipede biologists may refer to as poison claws, forcipules, maxillipeds, prehensors, prehensorial feet, forcipular telopodites, toxicognaths (Bonato et al. 2010) … you get the picture. Fangs. They look like this, when viewed from below:

multidentatus

Bothropolys multidentatus, a common lithobiid centipede from eastern North America, viewed from beneath. Photo by Joseph DeSisto.

The fangs are the things that look like fangs. Pretty cool, huh?

Lithobiid centipedes belong to the order Lithobiomorpha, which includes centipedes with flattened bodies, spiracles (breathing holes) on the sides of their body, and 15 pairs of legs as adults. They are also show anamorphic development, which means the young add legs as they grow until they reach the final 15. Those in the family Lithobiidae have spines or spurs on their legs, which are helpful in identification.

Without a microscope, all lithobiids look pretty much the same. Some are bigger than others, but here in the eastern U.S. none exceed an inch or so. But on a smaller scale, the diversity in body form is fantastic, and one of the reasons they are probably my favorite family of centipedes.

To tell the difference between males and females, we need to move our view to the rear end of the centipede, and look at it again from beneath. While males are pretty nondescript in this regard, the females have a set of gonopod claws, which they use to manipulate the eggs they lay. A female centipede can lay an egg and then carry it around with her until she finds a suitable place to leave it, then use her legs and claws to coat the egg in dirt for camouflage .

Gonopod Claws

The gonopod claws on a female lithobiid, Lithobius forficatus. Please excuse the red writing, I originally made this image for a poster. Photo by Joseph DeSisto.

But in a few North American lithobiids, the males make themselves known by other means. This is most obvious in the last two pairs of legs, which may be highly modified into strange, contorted forms. Here’s an example, viewed from the side:

A male centipede in the genus Pearsobius. Photo by Joseph DeSisto.

A male centipede in the genus Pearsobius. Photo by Joseph DeSisto.

Pearsobius is a poorly known genus from Virginia and North Carolina (Causey 1942). The specimen above is unidentified. There will be a later post devoted just to Pearsobius, but for now, let’s look at more pictures! Pictures are great.

Male Pearsobius again, this time viewed from above. Photo by Joseph DeSisto.

Male Pearsobius again, this time viewed from above. Photo by Joseph DeSisto.

These centipedes are about half an inch in length, but the “spike” on the femur of the last pair of legs is visible even without a microscope. Although impressive, the purpose of these structures is unclear. My best guess is that the females use them to recognize males of the same species. While butterflies might use colors to achieve this effect, and birds might use songs, female centipedes live their lives in leaf litter and soil, where sight are of little use, and they can’t hear. So in an area where multiple centipede species might roam the same patch of leaf litter, a female needs something she can feel to avoid getting friendly with a male of a different species.

Not all leg modifications are so striking. Here is the 15th pair of legs on a male Paitobius zinus, also from Virginia.

The 15th pair of legs on a male Paitobius zinus from western Virginia. Photo by Joseph DeSisto.

The 15th pair of legs on a male Paitobius zinus from western Virginia. Photo by Joseph DeSisto.

Not as cool as a massive spike, but the modification here (the long indent on one of the segments) is still enough to make Paitobius distinguishable from other lithobiid genera. However, in Paitobius zinus, this is not the most striking male modification. Uniquely in this species, the male and female fangs/forcipules are different. The female’s forcipules are normal, and look pretty much like the ones from earlier (on Bothropolys). The male’s however … well, they look like this:

The forcipules on a male Paitobius zinus. Photo by Joseph DeSisto.

The forcipules on a male Paitobius zinus. Photo by Joseph DeSisto.

Yeah.

So far, P. zinus is the only species known to have modified male forcipules, and nobody knows why they have these. Long, narrow fangs could be an adaptation to extracting prey from narrow spaces (like in the woodlouse-eating spider, Dysdera crocata) … but why aren’t they found in females? Usually when we find a structure that is present in one sex but not the other, the function is related to reproduction. But as far as we know, the only thing forcipules are used for is killing prey.

Crabill (1960) was the first to write about this phenomenon in P. zinus, and since then, not a single person has bothered to study it. Why? Because despite being totally and undeniably awesome, centipedes are hard, and barely anyone studies them. I am currently planning a summer collecting trip to Virginia, though, and while I’m there I’ll see if I can learn anything. I have no idea why this species is so strange, but whatever reason there is, I bet it’s amazing.

A big thank you is owed to Dr. Bill Shear at Hampden-Sydney College in Virginia, who kindly sent me the specimens of Pearsobius and Paitobius, which he collected.

Cited:

Bonato, L., G. Edgecombe, J. Lewis, A. Minelli, L. Pereira, R. Shelley, and M. Zapparoli. 2010. A common terminology for the external anatomy of centipedes (Chilopoda). ZooKeys 69: 17-51.

Causey, N.B. 1942. New lithobiid centipedes from North Carolina. Journal of the Elisha Mitchell Scientific Society 58: 79-83.

Crabill Jr., R.E. 1960. A remarkable form of sexual dimorphism in a centipede (Chilopoda: Lithobiomorpha: Lithobiidae). Entomological News 71: 156-161.

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.