Tag Archives: entomology

Nicotine, a Natural Insecticide

Nicotine, the addictive agent in cigarettes, comes from the leaves of tobacco plants (Nicotiana). Plants, of course, do not manufacture nicotine as a favor to smokers, but for their own benefit: nicotine is one of the most powerful insecticides in the world, highly effective at stopping hungry, leaf-munching pests in their six-footed tracks.

800px-Tabak_P9290021.JPG

Tobacco flowers and leaves. Photo by Joachim Mullerchen, licensed under CC BY 2.5.

Nicotine is a neurotoxin, and to understand how it works, you’ll need to understand a few things about the nervous system. Nerves are simply long, thin cells that run through your body, carrying signals as electrical impulses. Here’s the problem: at the junction between two nerve cells, or between a nerve and a muscle cell, there’s a space across which electrical impulses cannot travel. This space is called the synapse.

To keep the message going, the signal-sending nerve cell sends out an army of molecules called neurotransmitters, who boldly drift across the synapse like astronauts from space-ship to satellite. When a neurotransmitter arrives at the receiving nerve or muscle cell, it enters through a tube-shaped receptor molecule.

There are many kinds of neurotransmitters, each with its own unique receptor. Take acetylcholine, which carries signals from nerve cells to muscle cells. When you recoil from a hot stove, it’s acetylcholine that tells your muscles to get moving.

Synapse_blank.png

A synapse between two nerve cells. Figure in public domain.

If a poison kept all your acetylcholine receptors closed, you would be paralyzed: your muscles wouldn’t get any signals from the nervous system. If, on the other hand, the toxin kept receptors constantly open, your muscles would be constantly trying to move. You would go into convulsions, unable to control your body. Eventually you would exhaust yourself and die.

That’s how nicotine works (Zevin et al. 1998). In small doses, like in a cigarette, it works as a mild stimulant, keeping a few more receptors open than usual. In massive doses, like when a caterpillar eats a tobacco leaf, it works like a doorstop, keeping all acetylcholine receptors wide open. The unfortunate insect convulses, contracting all its muscles simultaneously until it runs out of energy and expires.

For many years, farmers used nicotine as a pesticide, spraying it over their crops to poison any hungry insects. However, nicotine is quite toxic to mammals, including humans. It isn’t sold as a pesticide anymore in the U.S. or Europe, replaced by neonicotinoids. The new pesticides are similar to nicotine, highly effective, and work in the same way, but are safer for people (not insects, of course).

128000114.lkRdGj8s.IMG_2051.JPG

The tobacco hornworm. Photo by Tom Murray, used with permission.

There are insects that eat tobacco leaves, and those insects have acquired an immunity to nicotine. The best-known example is the tobacco hornworm (Manduca sexta), a big, fat, bright green caterpillar that ultimately transforms into a hawkmoth. In fact, these caterpillars have evolved the ability to store nicotine in their own bodies, making themselves toxic to caterpillar-eating predators. Experiments have shown that wolf spiders normally avoid tobacco hornworms, but if the caterpillars are fed a diet lacking in nicotine, the spiders attack without hesitation (Kumar et al. 2013).

Cited:

Kumar P., S.S. Pandit, A. Steppuhn, and I.T. Baldwin. 2013. Natural history-driven, plant-mediated RNAi-based study reveals CYP6B46’s role in a nicotine-mediated antipredator herbivore defense. Proceedings of the National Academy of Sciences U.S.A. 111(4): 1245-1252.

Zevin S., S.G. Gourlay, and N.L. Benowitz. 1998. Clinical pharmacology of nicotine. Clinics in Dermatology 16(5): 557-564.

The Scaly Crickets

by Joseph DeSisto

Among many new species named today, some of the most unusual were three new crickets from Southeast Asia (Tan et al. 2015). These crickets belong to the obscure and poorly-known family Mogoplistidae, cousins to the more recognizable (and audible) field crickets (Gryllidae). They look like field crickets too, except that their bodies are covered in scales.

A scaly cricket (Arachnocephalus vestitus). © Entomart.

A scaly cricket (Arachnocephalus vestitus). © Entomart.

When you touch a butterfly’s wings, you might notice a fine, powdery substance rubbing off on your fingers. The powder is made up of microscopic scales, which cover the wings of butterflies and moths. Scales give the wings their color, but they also provide insulation and protect the wings during flight. Perhaps most importantly, scales can fall off and make the wings slippery. This allows butterflies and moths to evade a careless hand as easily as a wet bar of soap.

The scientific name for butterflies and moths is Lepidoptera, which translates to “scaly wing” — scales are one of the most important features defining the group. However, many other groups of insects also have scales. Mosquitoes and silverfish have them, and so do scaly crickets.

The scales of a scaly cricket (Ornebius formosanus). Figure from Yang and Yen (2001), licensed under CC BY 2.0.

The scales of a scaly cricket (Ornebius formosanus). Figure from Yang and Yen (2001), licensed under CC BY 2.0.

Cricket scales, like those of butterflies and mosquitoes, are microscopic, powder-like, and easily shed. To really appreciate their beauty, a scanning electron microscope is needed. The first look came in 2001, when Yang and Yen published the first high-resolution images of cricket scales.

Aside from being scaly, scaly crickets aren’t all that unusual. They are adaptable, able to eat decaying plants as well as other insects, and they tend to live in moist sandy habitats. No scaly crickets are capable of flight, and females lack wings entirely, but the males do have small wings which they rub together to make chirping sounds (Love and Walker 1979). Click on the audio file below to listen to an amorous male scaly cricket (recorded by Thomas J. Walker).

Of the three new species, two were found in the Sakaerat Biosphere Reserve, in Thailand. This reserve consists mainly of high-altitude dry forest, with a few grasslands, and is home to many endangered species including tigers and giant black squirrels.

The third cricket is native to Pulau Ubin, an island off the coast of Singapore. Pulau Ubin is one of the last remaining wild areas in the already tiny country. Singapore’s government has been eager to develop portions of the island, but in recent years tourism has become more profitable. Fear of losing foreign visitors has encouraged officials to protect, rather than level, valuable habitat. For now, the status of the new scaly crickets appears secure, but in rapidly urbanizing Southeast Asia, nothing is certain.

A scaly cricket (Mogoplistes brunneus). © Entomart.

A scaly cricket (Mogoplistes brunneus). © Entomart.

Cited:

Love R.E. and T.J. Walker. 1979. Systematics and acoustic behavior of scaly crickets (Orthoptera: Gryllidae: Mogoplistinae) of eastern United States. Transactions of the American Entomological Society 105:

Tan M.K., P. Dawwrueng, and T. Artchawakom. 2015. Contribution to the taxonomy of scaly crickets (Orthoptera: Mogoplistidae: Mogoplistinae). Zootaxa 4032(4): 381-394.

Yang J. and F. Yen. 2001. Morphology and character evaluation of scales in scaly crickets (Orthoptera: Grylloidea: Mogoplistidae). Zoological Studies 40(3): 247-253.

Changes

by Joseph DeSisto

The idea that an animal that looks like this:

An early-stage caterpillar of the promethea moth (Callosamia promethea). Photo by Joseph DeSisto.

An early-stage caterpillar of the promethea moth (Callosamia promethea). Photo by Joseph DeSisto.

can transform into something like this:

An adult promethea moth. Photo by Tom Murray, used with permission.

An adult promethea moth. Photo by Tom Murray, used with permission.

has captivated us for centuries. The caterpillar and moth above belong to the species Callosamia promethea, commonly called the promethea moth. Prometheas can have wingspans approaching 4 inches across, and throughout their eastern North American range they are some of the biggest moths around. The moth is truly a spectacular beast. What often goes unappreciated, however, are the changes that go on before the caterpillar even forms its cocoon.

All caterpillars have to molt several times before they are large enough to go through metamorphosis. The stages between molts are called instars, and sometimes successive instars can look very different from one another.

The first photo was of a caterpillar in its second instar, meaning it has molted once since it hatched out of an egg. At this point the caterpillar has grown from nearly microscopic to a respectable centimeter or so — now it’s ready to molt again. It does so by splitting the front of its exoskeleton and, slowly and patiently, pulling itself out:

From second to third instar: a molting promethea caterpillar. Photo by Joseph DeSisto.

From second to third instar: a molting promethea caterpillar. Photo by Joseph DeSisto.

The old, empty skin is left behind:

The left-over exoskeletons of just-molted third instar caterpillars. Photo by Joseph DeSisto.

The left-over exoskeletons of just-molted third instar caterpillars. Photo by Joseph DeSisto.

When we started rearing these caterpillars in the lab, I wasn’t familiar with their life history. You can imagine my surprise when a container full of black-and-yellow-striped caterpillars, overnight, became a container full of these charming little creatures:

A third instar promethea caterpillar. Photo by Joseph DeSisto.

A third instar promethea caterpillar. Photo by Joseph DeSisto.

Promethea caterpillars are generalists and eat leaves off a variety of woody plants — these ones are munching on black cherry (Prunus serotina).

Third (left) and second (right) instar promethea caterpillars. Photo by Joseph DeSisto.

Third (left) and second (right) instar promethea caterpillars. Photo by Joseph DeSisto.

Why do the caterpillars change so radically and suddenly? That question remains very much unanswered. Perhaps the two instars simply have slightly different lifestyles, and different lifestyles require different adaptations. Or maybe having two different-looking life stages keeps predators from developing an accurate “search image.” In other words, by the time a bird learns to recognize the second instar as prey, it changes into a new, unfamiliar caterpillar.

Tomorrow I leave to spend a week in Arizona, New Mexico, and Texas. I’m supposed to spend that time looking for caterpillars and moths although I hope to see many other interesting animals — scorpions, rattlesnakes, and giant centipedes are at the top of my list. No writing while I’m gone, sadly, but plenty of picture-taking, so brace yourselves.

Potato Wars: Meet the Gelechiids

by Joseph DeSisto

Today’s story comes from the tiny but remarkable twirler moths, the Gelechiidae. The moths themselves are small and typically brown, attracting little attention, while the caterpillars go by names like splitworm, bollworm, pinworm, tuberworm, and so on, usually referring to the plant tissues they consume.

Human interest in twirler moths, then, is largely focused on their relationships with the plants that both humans and twirlers relish — potatoes, tomatoes, grains, almonds, and many others.

The gelechiid caterpillar Chionodes pseudofondella, freshly coaxed from its silken shelter. Photo by M.J. Hatfield, licensed under CC BY-ND-NC 1.0.

The gelechiid caterpillar Chionodes pseudofondella, freshly coaxed from its silken shelter. Photo by M.J. Hatfield, licensed under CC BY-ND-NC 1.0.

Twirler caterpillars live sheltered lives — they typically either live inside twigs, fruit, leaves, or other plant tissues, or else use silk to roll leaves into shelters. This way the caterpillars can dine in relative peace, with fewer predators able to find and attack them.

The opening to a shelter in mountain mint, made by the caterpillar above.

The opening to a shelter in mountain mint, made by the caterpillar above. Photo by M.J. Hatfield, licensed under CC BY-ND-NC 1.0.

Shelters can be effective against spiders and wasps, but they haven’t stopped humans from using all kinds of strategies, from pesticides to natural predator, to keep twirler caterpillars out of their crops. With good reason — many of these caterpillars cost farmers a huge portion of their annual yield.

Today we are going to focus on one of these moths, the Guatemalan potato moth, Tecia solanivoria (GPM). GPM caterpillars feed underground by boring into a potato and hollowing out a set of tunnels, in which they live until ready to emerge as adult moths. By eating out the inside of the potato, the caterpillars not only damage the crop themselves, they also allow fungi to enter the potato and begin the decomposition process, resulting in a rotten vegetable.

The Guatemalan potato moth's caterpillar, in all its glory. Photo from Hayden et al. (2013).

The Guatemalan potato moth’s caterpillar, in all its glory. Photo from Hayden et al. (2013).

The caterpillars can feed on potatoes both before and long after harvest. As a result, they are easily spread when infested potatoes are shipped across long distances. Although GPM is native to Guatemala, it was first discovered in Costa Rica where it had been introduced in imported potatoes. Entomologists estimate that the introduction occurred in 1970, but the species was not formally described until three years later (Povolny 1973).

Why so long between introduction and description? Here I must editorialize — if Central America had had an active expert in gelechiid taxonomy, the species that was causing so much damage would surely have been discovered much earlier, perhaps even before the species ever left Guatemala! Instead the species was described by a Czech taxonomist, by which time Central American farmers were reporting 20-40% crop losses to the unnamed pest (Povolny 1973). The “outsourcing” of tropical biodiversity research to scientists in first-world countries can have dire consequences.

For reference, here's a map showing Central America and northwestern South America. GPM is native to Guatemala in the northwest, then quickly spread through Central America, Venezuela, Colombia, and Ecuador. Map data: Google, Landsat.

For reference, here’s a map showing Central America and northwestern South America. GPM originated in Guatemala (upper left) and has quickly spread southeast as far as Ecuador and Colombia. Click to enlarge. Map data: Google, Landsat.

Before 1970, the most significant potato-eating caterpillar in Latin America was the potato tuberworm (Phthorimaea operculella — try saying that out loud). Unlike GPM, the tuberworm is a leaf-miner, munching its way through the 2-dimensional world inside leaves. After its introduction to Costa Rica, however, GPM saw a meteoric rise, and quickly stole the show as the most economically injurious caterpillar for Latin American potato growers (Carrillo and Torrado-Leon 2013). In 1983 GPM was accidentally imported (via infested potatoes) into Venezuela from Costa Rica, and South America became the new front in the moth’s conquest. By 1996 the caterpillars had reached Ecuador, and in 1999 a population was even introduced to the Canary Islands off the coast of Northwest Africa.

Managing GPM is an economic necessity. Unfortunately, this can be difficult since once the caterpillar hatches and starts making its tunnels inside a potato, you’ve pretty much lost the potato. Pesticides are generally targeted toward the more vulnerable eggs and adult moths, but these stages are short-lived. Timing is crucial, and only pesticides applied at the right stage will reduce crop losses. Despite this, potato growers frequently err on the side of caution, applying pesticides intensively throughout the growing season (Carrillo and Torrado-Leon 2013). This is not only a waste of money, it can also lead to the moths becoming resistant to the pesticides, not to mention the environmental and human safety consequences of pesticide overuse.

A pinned specimen of the Guatemalan potato moth. Photo from Hayden et al. (2013).

A pinned specimen of the Guatemalan potato moth. Photo from Hayden et al. (2013).

The most effective methods of reducing GPM infestation are not chemical but cultural (Gallegos et al. 2002). Growers can help protect their plants by tilling the soil to break up clumps (havens for moths and eggs), planting their potatoes deeper in the soil, and removing “leftover” potatoes from the soil.

Here’s the twist: under certain conditions, it can actually benefit the farmer to let the caterpillars feed.

In 2010, Poveda and colleagues experimented with GPM abundance in potato fields in Colombia. Surprisingly, fields in which caterpillars were allowed to feed in moderation actually showed higher total yield than when caterpillars were completely excluded. It turns out that when caterpillars feed, the chemicals in their saliva are strewn about the potato, and the plant is able to recognize and react to these chemicals.

Flowers from a potato plant. Photo by Keith Weller, in public domain.

Flowers from a potato plant. Photo by Keith Weller, in public domain.

Each potato plant contains many tubers, the things we call potatoes. If less than 10% of these are infested with caterpillars, the plant compensates by diverting resources to the remaining tubers. The result: a greater number of extra-large potatoes, and an increase in overall yield. Plants with limited caterpillar infestations yielded 2.5 times as much useable potato mass as plants in which there were no caterpillars at all.

The lesson? Plant-insect relationships are complicated, and understanding the subtle details can matter. So can the taxonomy of small, “boring” moths. There are a lot of important things we wouldn’t know about GPM if it weren’t for the hard work and dedication of entomologists from Colombia to the Czech Republic. With invasive pests an increasing problem, we need to make sure to invest in both applied and basic research, and study even the insects that most people would rather ignore.

This post marks the start of a kind of experiment for me. Starting here, I will be posting a new article every Tuesday and Thursday. Here’s the catch: each post will focus on a different family of invertebrates, and I can’t cover the same family twice! The goal is to try and write about as many families as possible, starting with Gelechiidae.

Cited:

Carrillo D. and E. Torrado-Leon. 2013. Tecia solanivora Povolny (Lepidoptera: Gelechiidae), an Invasive Pest of Potatoes Solanum tuberosum L. in the Northern Andes. In: J.E. Pena (Ed.), Potential Invasive Pests of Agricultural Crops (126-136). Boston, Massachusetts: CABI.

Gallegos P., J. Suquillo, F. Chamorro, P. Oyarzun, H. Andrade, F. Lopez, C. Sevillano, et al. 2002. Determinar la eficiencia del control quimico para la polilla de la papa Tecia solanivora, en condiciones del campo. In: Memorias del II Taller Internacional de Pollila Guatemalteca Tecia solanivora, Avances en Investigacion y Manejo Integrado de la Plaga, 4-5 June 2002, Quito, Ecuador pp. 7.

Hayden, J.E., S. Lee, S.C. Passoa, J. Young, J.F. Landry, V. Nazari, R. Mally, L.A. Somma, and K.M. Ahlmark. 2013. Digital Identification of Microlepidoptera on Solanaceae. USDA-APHIS-PPQ Identification Technology Program (ITP). Fort Collins, CO. 7 July 2015 <http://idtools.org/id/leps/micro/&gt;

Povolny D. 1973. Scrobipalpopsis solanivora sp. n. — a new pest of potato (Solanum tuberosum) from Central America. Acta Universitatis Agriculturas, Facultas Agronomica 21(1): 133-146.

The Many Uses of Centipede Legs

by Joseph DeSisto

This post started out titled “My Favorite Centipede Genus,” but that could never last. I have too many favorites. Right now, Theatops is my 6th, but things can always shift around. Theatops has no official common name, but in the spirit of this blog, I’m going to make one up right now: the forcep centipedes. I’ll explain why.

Forcep centipedes are not especially diverse, with only six species known worldwide, four of which are strictly North American. They are, however, large and impressive, and reasonably common through much of their range. A week or so ago Derek Hennen sent me a speciment of Theatops posticus, one of two species found in the eastern U.S.:

A Theatops posticus from Ohio, sent to me by Derek Hennen. Photo by Joseph DeSisto.

A Theatops posticus from Ohio, sent to me by Derek Hennen. Photo by Joseph DeSisto.

Modified hind legs are common in centipedes, especially in the scolopendromorphs (centipedes with 21 or 23 pairs of legs). A paper published today in ZooKeys reviewed the uses for hind legs in the family Scolopendridae (Kronmüller and Lewis 2015), which includes some of the most impressive centipedes, i.e., the foot-long giants in the genus Scolopendra.

Their conclusions were that the hind legs of scolopendrids have a wide variety of uses, the least of which is walking. In Scolopendra, the legs are covered in short spines and are used to capture prey, guide courtship, and grapple with predators. After an intimidating display, a Scolopendra can grab onto you with its hind legs, then rear its whole body around to inject venom with its fangs — which are themselves modified legs.

big_46141

Figure 2 from the Kronmüller and Lewis paper, showing uses for the spiny modified legs of Scolopendra. The threat display (A and B) would be quite intimidating coming from a centipede that can reach 12 inches or more in length. From Kronmüller and Lewis (2015), licensed under CC BY 4.0.

Hind legs can also mimic antennae, so that predators like birds are tricked into attacking the less vulnerable rear end of the centipede. Attackers are then met with an unpleasant surprise when the real head makes its move! This strategy is most obvious in Scolopendra heros arizonensis, where the trunk is orange but the first and last few segments are jet black. But many non-scolopendrids also have rear legs that resemble antennae, especially the scutigeromorphs or “house centipedes,” whose legs readily detach if they are caught.

Scolopendra heros arizonensis, from the deserts of the southwestern U.S. and Mexico. The

Scolopendra heros arizonensis, from the deserts of the southwestern U.S. and Mexico. The “mimicry” between the front and rear segments might confuse predators into attacking the wrong end. Photo by Aaron Goodwin, licensed under CC BY-ND-NC 1.0.

Scolopendrids can also use their legs to climb, even on the ceilings of caves. Scolopendra gigantea, a South American giant that can reach 12 or more inches in length, has been observed hanging from its rear legs in Venezuelan caves and snatching bats out of the air (Molinari et al. 2005). This phenomenon was even featured in the first episode of David Attenborough’s Life in the Undergrowth television series.

Then there’s the flag-tailed Alipes, which uses its hind legs to make a hissing noise … really you should just read the paper. It’s a peer-reviewed journal article, but it is publicly accessible here and, for the most part, readable by a non-expert.

Miscellaneous scolopendrid rear legs, modified in different ways. The flag-tailed centipede (C) is probably the strangest, and its legs can be rubbed together to make a loud hissing noise. Photo from Kronmuller and Lewis (2015), licensed under CC BY-NA 4.0.

Miscellaneous scolopendrid rear legs, modified in different ways. The flag-tailed centipede Alipes (C) is probably the strangest, and its legs can be rubbed together to make a loud hissing noise. Photo from Kronmüller and Lewis (2015), licensed under CC BY 4.0.

All of this was a very long way of saying that Theatops isn’t really that special … probably. Actually, Theatops was not covered in this paper, since it belongs not to Scolopendridae but to the less-known family Plutoniumidae. And yes, that’s the real name.

In the East we have two species: T. posticus and T. spinicaudus. The main difference between the two is that spinicaudus has a pretty large spine on the last pair of legs, while posticus does not. So, I here propose we call posticus the smooth-tailed forcep centipede and spinicaudus the spiny-tailed forcep centipede.

Smooth-tails are found through most of the eastern U.S., from Connecticut south to Florida and west to eastern Texas (Shelley 2002). A separate population of smooth-tails is found in the West (along with two other Theatops species), in western Arizona and southern California and Nevada, but this may represent a separate species.

Spiny-tails, meanwhile, are abundant but geographically restricted: there are two populations, one in the southern Appalachians and one in the Ozarks (Shelley 2002). Apparently this species prefers mountain habitats, since spinicaudus is not found in the area between the two mountain ranges.*

The forcep-like hind legs of the smooth-tailed forcep centipede, Theatops posticus. Photo by Joseph DeSisto.

The forcep-like hind legs of the smooth-tailed forcep centipede, Theatops posticus. Photo by Joseph DeSisto.

*[Actually, this is why I’m looking for Theatops specimens in the first place — to obtain genetic data so I can figure out how/when they came to inhabit their bizarre geographic ranges.]

The modified hind legs immediately make me think of an earwig, and they appear to be useful for grabbing things — but what are these centipedes grabbing? To start, they certainly do grab the forceps I used to pick them up during my May trip to the southern Appalachians. If you try and pick up one of these centipedes, they will simultaneously grab you with their legs and inject venom with their fangs.

But then, why attack with non-venomous hind legs, when forcep centipedes can and do use their venom-injecting fangs? Perhaps the hind legs give the centipede leverage with which to inflict a longer-lasting, more painful bite. It’s possible, and scolopendrids certainly do it, but I think there may be more to this story.

The business end of Theatops posticus -- the fangs beneath the head pack a healthy dose of venom, used to dispatch prey. Photo by Joseph DeSisto.

The business end of Theatops posticus — the fangs beneath the head pack a healthy dose of venom, used to dispatch prey and make predators cry. Photo by Joseph DeSisto.

The whole last segment of a forcep centipede’s body, including the legs, is heavily protected with extra-thick cuticle. The exoskeleton on the rear legs and segment is about as thick as that around the fangs at the front of the body, which is usually the most heavily protected part of a centipede. I think that Theatops species might use their hind legs to attack dangerous prey — spiders, or maybe even other centipedes. In this way, a forcep centipede can inflict its deadly bite only after the prey has been subdued, so avoiding injury.

It’s only a hypothesis, and one that requires some testing. I have tried feeding smaller centipedes to Theatops, who attacked and fed with gusto, but never used involved their rear legs in the process. So for now, we really don’t know why forcep centipedes have such strange hind legs. All we know is that they are strange, oddly captivating, and will likely remain that way for a long time.

A couple of things. First, I want to thank Derek Hennen, a Masters student at the University of Arkansas, for sending me the specimen photographed here. Actually, this is just one of many centipedes he has sent me! He also has his own blog, Normal Biology, featuring insects, millipedes, and even the occasional centipede.

On July 19 I will be speaking about centipedes, millipedes, and why they’re amazing at the Schoodic Research and Education Center in Acadia National Park (Maine)! This is a public program, part of the bioblitz going on that same weekend in Acadia. If you’re in the area, stop by! More information is available here.

Cited:

Kronmüller, C. and J.G. Lewis. 2015. On the function of the ultimate legs of some Scolopendridae (Chilopoda, Scolopendromorpha). ZooKeys 510: 269-278.

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.

Shelley, R. 2002. A synopsis of the North American centipedes of the order Scolopendromorpha (Chilopoda). Memoir of the Virginia Museum of Natural History 5: 1-108.

Key-making: Illustrating the Stone Centipedes of New England

by Joseph DeSisto

Have you been waiting on the edge of your seat for an identification key to the New England stone centipedes? Do you often find yourself up late at night, eagerly searching for recent articles in taxonomic journals, only to have your chilopodological hopes dashed?

Well, your wait is (nearly) over! This week I started illustrating a key to the stone centipedes of New England. A total of 18 species are represented, the product of more than a year of relentlessly identifying hundreds upon hundreds of museum specimens, but the key is finally coming! It will be ready to send off to a journal by the end of the semester.

It will be ready. It will be ready. It will be ready.

Fangs! Photo by Joseph DeSisto.

Fangs! Because, fangs! Photo by Joseph DeSisto.

Anyway, I spent today working on line drawings, and I’ve included a few outlines here — note that the images below are not the images that will appear in the key itself. Rather, these are preliminary outlines I have made to provide a template for the final illustrations. They still need a lot of work, including shading.

The outline of the photo from earlier looks like this:

The prosternum (with fangs!) of Bothropolys multidentatus, one of New England's largest and commonest stone centipedes. Illustration by Joseph DeSisto.

The prosternum (with fangs!) of Bothropolys multidentatus, one of New England’s largest and commonest stone centipedes. Illustration by Joseph DeSisto.

Not bad for a first go, huh? Actually it was my fourth or fifth go, but moving on …

How does this work? First, I use a fancy microscope and an extra-fancy image-stacking computer program to make nice clear images of a centipede feature like the one above. Then I print out that photograph, and use a micron pen to outline, directly on the picture, the drawing I want to create. When the photograph is sufficiently defiled by lines, scribbles crossing out lines, and more lines, I put the paper on a light box and copy my outline onto tracing paper.

Then I copy that onto another piece of tracing paper. And another. And another, until finally I have one that’s good enough to look at without cringing.

The centipede from earlier is Bothropolys multidentatus, a common and large centipede in New England. Below I’ve illustrated the pores on the coxae (basal segments) of the 14th pair of legs:

The 14th coxae, viewed from below, of Bothropolys multidentatus. Illustration by Joseph DeSisto.

The 14th coxae, viewed from below, of Bothropolys multidentatus. Illustration by Joseph DeSisto.

The last two illustrations, you may have noticed, are roughly symmetrical. Real specimens are hardly ever that perfect — to make the illustrations look a bit nicer, and fit better on the page, I traced one half first and then traced its mirror image. In other words, the outlines are symmetrical because each side of the line drawing actually shows the same side of the original specimen.

Here’s a special one. This sexy leg belongs to a male Nadabius aristeus, a common but smaller New England centipede. There are two important features I’m trying to show here. First, there are two claws, rather than just one, at the end of the leg. Second, the hairy crest on the tibia is unique to males the genus Nadabius.

One of the terminal legs of a male Nadabius aristeus. Illustration by Joseph DeSisto.

One of the terminal legs of a male Nadabius aristeus. The tarsus/foot is at the bottom. Illustration by Joseph DeSisto.

Female centipedes be like, damn!

A Tetragnathid Spider Walks into a Bar …

by Joseph DeSisto

… and the bartender asks, “Why the long fangs?”

A Tetragnatha species from Vermont. You might have to look closely to see the fangs, they are quite inconspicuous. Photo by Tom Murray.

A Tetragnatha species from Vermont. You might have to look closely to see the fangs, they are quite inconspicuous. Photo by Tom Murray, used with permission.

But seriously. Long-jawed orb-weaver spiders, family Tetragnathidae, sport some of the longest, scariest, most ridiculous-looking fangs in the spider world. Why?

As their name suggests, long-jawed orb-weavers build orb-webs, which are spiral-shaped webs with radiating spokes. Walk along the edge of a pond when the weather warms up and you may see horizontal orb-webs covering the vegetation just above the water. These webs are built by tetragnathid spiders hoping to catch insects that spend their larval stages in the water before undergoing metamorphosis and flying off. Many mosquitos end their lives early in this way, without even completing their first flight.

The web of Tetragnatha laboriosa. Can you find the spider? Photo by Alex Wild, in public domain.

The web of Tetragnatha laboriosa. Can you find the spider? Photo by Alex Wild, in public domain via Insects Unlocked.

Since long-jawed orb-weavers are predatory, and their fangs are used to inject prey with venom, we might expect that long fangs are adaptations for dispatching a particular kind of prey. This makes sense — other spiders with large fangs often specialize in dangerous prey. For example, there is an ant-mimicking jumping spider (Myrmarachne plataleoides) from Southeast Asia with fangs even longer than those of tetragnathids. Myrmarachne uses its fangs to capture — you guessed it — stinging ants.

A male weaver-ant-mimicking jumping spider, showing off his freakishly long fangs.

A male weaver-ant-mimicking jumping spider, showing off his freakishly long fangs. “Myrmarachne plataleoides male at Kadavoor” © 2010 Jeevan Jose, Kerala, India is used here under a Creative Commons Attribution-ShareAlike 4.0 International License.

But look a little closer, and it turns out that the long fangs of Myrmarachne aren’t crucial for ant-killing. How do we know this? Because the females don’t have them. They have fangs of course, but only normal-sized ones, and these work for taking out venomous ants just fine. The females may even be better predators, since they are more accurate ant mimics.

The males are lousy hunters. Their ridiculous fangs mean they aren’t very good at mimicking ants, and what’s more, their fangs don’t even have ducts for injecting venom. Instead, they use their fangs as swords in male-to-male combat (Pollard 2009).

The female Myrmarachne plataleoides, same species as the male above. She has more ordinary-sized fangs, but is a better ant mimic and so a more effective than the male, who instead uses his fangs as swords against other male spiders. Photo by Sean Hoyland, in public domain.

The female Myrmarachne plataleoides, same species as the male above. She has more ordinary-sized fangs, but is a better ant mimic. Photo by Sean Hoyland, in public domain.

Tetragnathids, living in their orb-webs, don’t have to worry too much about ants. In fact their prey are mostly defenseless flies and other short-lived insects emerging from the water. Like Myrmarachne, their enlarged fangs have a reproductive function, but instead of males using them to fight off other males, both males and females use them during courtship.

Here’s how it works (see Eberhard and Huber 1998). When a male long-jawed orb-weaver finds a female’s web, he approaches cautiously — if the female is receptive, there is a chance she will not eat him. He starts by signalling his presence with precisely timed “twangs” of her web, strumming the orb’s spokes like guitar strings. If she approves, she allows him to continue tapping at her web and her body with his legs.

The orchard spider (Leucauge venusta), a common tetragnathid in North and Central America. Photo by Andrea Westmoreland, licensed under CC BY-SA 2.0.

The orchard spider (Leucauge venusta), a common tetragnathid in North and Central America. Photo by Andrea Westmoreland, licensed under CC BY-SA 2.0.

Now the fangs come in. The female orb-weaver opens hers wide, the male moves forward, and their fangs interlock. At the base of each fang is a ridge or tooth that helps keep the couple together, so that the male spider can only leave if the female allows him to do so.

When the male has finished transferring his sperm, the female releases him from her grip and he can leave. Post-mating cannibalism in tetragnathids is rare, despite being common in other families of orb-weaving spiders (i.e., araneids).

Tetragnatha laboriosa, the spider that weaved the web shown earlier. Photo by Alex Wild, in public domain.

Tetragnatha laboriosa, the spider that weaved the web shown earlier. Photo by Alex Wild, in public domain via Insects Unlocked.

Two of the photos used in this article are from Insects Unlocked, a project run by the infamous macro-photographer Alex Wild. The goal of this project is to generate high-quality photographs of insects and other invertebrates for the public domain, available to everyone, everywhere, for free. If you enjoy this blog and others that depend on freely available insect photography, please consider donating to Insects Unlocked.

Cited:

Eberhard, W.G. and B.A. Huber. 1998. Courtship, copulation, and sperm transfer in Leucauge mariana (Araneae, Tetragnathidae) with implications for higher classification. Journal of Arachnology 26(3): 342-368.

Pollard, S.D. 2009. Consequences of sexual selection on feeding in male jumping spiders (Araneae: Salticidae). Journal of Zoology 234(2): 203-208.

Mega-Diverse Megaselia: Flies in the News

by Joseph DeSisto

The phorid fly genus Megaselia contains around 1600 known species, but there are estimates that the genus may contain as many as 30,000 species in total. These flies made the news this year when 30 new species (and 16 already-known species) were discovered in the city limits of Los Angeles (Hartop et al. 2015). This is amazing but not unheard of for Megaselia — an earlier study in Cambridge, England revealed 53 species in a single garden (Disney 2001).

A female Megaselia aurea, scavenging on a dead cricket. Photo by Brian V. Brown and Wendy Porras, used under CC BY 4.0.

A female Megaselia aurea, scavenging on a dead cricket. Photo from Brown and Porras (2015), licensed under CC BY 4.0.

Diversity in Megaselia, however, goes much deeper than a simple species tally. In terms of behavior and ecology, diversity can be awe-inspiring, even within a single species.

Megaselia adults are great, and some of the largest phorid flies around. but the larvae can be just as interesting. Many species are scavengers, and some feed on carrion;  Others are parasites of vertebrates (like bot flies), and still others live inside other insects. Most recently, scientists in Mexico discovered that one species, Megaselia scalaris, is a parasitoid of the tarantula Brachypelma vagans (Machkour-M’Rabet et al. 2015). The tarantula examined contained more than 500 fly larvae which, had the spider not been killed for study, would have ultimately eaten their host alive.

Megaselia scalaris, a fly with incredibly diverse ecological roles. Photo by Charles Schurch Lewallen, licensed under CC BY 3.0.

Megaselia scalaris, a fly with incredibly diverse ecological roles. Photo by Charles Schurch Lewallen, licensed under CC BY 3.0.

Aside from being amazing in itself, this find is significant because M. scalaris already has an incredibly diverse range of lifestyles — the examples here come from a review paper by Disney (2008). In addition to acting as parasitoids on a wide range of arthropods, scalaris larvae have been observed eating decaying plant matter, dung, bacteria and other microorganisms, the leaves and seeds of live plants, already-dead insects, and carrion.

Speaking of carrion, scalaris larvae are well-known for burrowing through up to six feet of soil to feed on human corpses in their coffins. They have also been observed in honey bee hives, scavenging on dead bees, and in amphibian egg masses, feeding on the developing tadpoles. A few specimens were found on the mouthparts of a land crab, where they were apparently eating bits of food the crab’s food.

I could go on … and I will. Sea turtle eggs, shoe polish, a preserved snake specimen recently removed from alcohol, the wounds of living animals from humans to pythons to poison dart frogs, highly toxic millipedes, blue emulsion paint …

Cited:

Brown, B.V. and W. Porras. 2015. Extravagant female sexual display in a Megaselia Rondani species (Diptera: Phoridae). Biodiversity Data Journal 3: e4368. doi: 10.3897/BDJ.3.e4368

Disney, R.H.L. 2001. The scuttle flies (Diptera: Phoridae) of Buckingham Palace Garden. The London Naturalist 80: 245–258.

Disney, R.H.L. 2008. Natural History of the Scuttle Fly, Megaselia scalaris. Annual Review of Entomology 53: 39-60.

Hartop, E.A., B.V. Brown, and R.H.L. Disney. 2015. Opportunity in our ignorance: urban biodiversity study reveals 30 new species and one new Nearctic record for Megaselia (Diptera: Phoridae) in Los Angeles (California, USA). Zootaxa 3941(4): 451-484.

Machjour-M’Rabet, S., A. Dor, and Y. Henaut. 2015. Megaselia scalaris (Diptera: Phoridae): an opportunistic endoparasitoid of the endangered Mexican redrump tarantula, Brachypelma vagans (Araneae: Theraphosidae). Journal of Arachnology 43(1): 115-119.7

Common Names for a Few Centipedes

by Joseph DeSisto

Few, if any, centipedes have common names. Presumably this is because they are often perceived as being uncharismatic. Here’s why they should get common names:

1) Centipedes are too charismatic.

2) Yes they are.

Below I’ve listed every species of soil centipede known from New England. Soil centipedes belong to the order Geophilomorpha, one of four centipede orders found in North America — so this list is far from complete. I’ve provided a Latin name, a proposed common name, and a brief explanation.

Arenophilus bipuncticeps, the northern short-clawed centipede

Northern because it’s the only Arenophilus found in the northeastern U.S., short-clawed because the claws on its last pair of legs are short and stubby and adorable.

Geophilus vittatus, the diamondback soil centipede

This is one of the prettiest centipedes around, and here in New England, we are lucky because it is also one of the commonest. It is a pale yellow like most centipedes, but with dark diamond-shaped markings running down the back. They are found in a variety of habitats, but are especially easy to find if you peel loose bark off dead stumps and logs.

The diamondback soil centipede (Geophilus vittatus), one of my favorites. You can find this centipede in the northeastern United States by peeling away loose bark from dead stumps and logs. Photo by Tom Murray.

The diamondback soil centipede (Geophilus vittatus), one of my favorites. Photo by Tom Murray.

Geophilus mordax, the pitted soil centipede

G. mordax is a strange centipede, and in reality probably includes two species: mordax in the south and virginiensis in the northern part of its range. For now, though, the two species are united by the presence of pit-like structures (sacculi) on each of the sternites or belly plates.

Geophilus cayugae, the montane soil centipede

According to Crabill (1952) G. cayugae prefers high elevations. Other than that, this species isn’t all that distinct.

Geophilus terranovae, the Newfoundland soil centipede

Here’s a cool one. Terranovae was described by Palmen in the 1950s from Newfoundland, and since no one had recorded it elsewhere, the centipede was assumed to be endemic to Newfoundland. But just this year, I found specimens of terranovae from New Hampshire, so although this is clearly a boreal species, it has a much wider range than previously thought.

Geophilus flavus, the boreal yellow-headed soil centipede

This is one of our largest soil centipedes, an introduced species from Europe. It is also yellow-white, with a darker head, and often found in gardens. This species is common in my home state of Maine but I have yet to find any in Connecticut. I suspect this is because G. flavus prefers a more northern climate, with cooler temperatures and pine-dominated forests.

This name is a little long, but there are a lot of soil centipedes out there. It looks like long names might just have to be the norm.

The venom-injecting fangs of the northern yellow-headed soil centipede (Geophilus flavus). Photo by Joseph DeSisto.

The venom-injecting fangs of the boreal yellow-headed soil centipede (Geophilus flavus). Photo by Joseph DeSisto.

Strigamia bothriopus, the red pin-head centipede

Species in the genus Strigamia are a mix of beautiful, weird, and horrifying. Many are brightly colored, and in New England bothriopus is one of the prettiest, the vivid red hue of a Maraschino cherry. They also have tiny heads, which is sort of adorable, until you learn what they’re for.

Strigamia have an extra claw on their venom-injecting fangs, causing them to look sort of like a can-opener. In function this is not inaccurate, but instead of opening cans, pin-head centipedes use their claws to open up the abdomens of insects. The tiny head can then be inserted into the insect — this way, Strigamia can lap up the nutritious insides of its prey without having to chew through lots of exoskeleton.

Strigamia chionophila, the boreal pin-head centipede

Chionophila is similar to bothriopus, but smaller and less brightly colored. This species is also more common in boreal habitats, gradually replacing bothriopus as the climate cools to the north.

The red pin-head centipede (Strigamia bothriopus). Photo by Tom Murray.

The red pin-head centipede (Strigamia bothriopus). Photo by Tom Murray.

Pachymerium ferrugineum, the long-jawed shore-crawler

This is by far my favorite New England soil centipede, but unfortunately it is one of the least common. The shore-crawler gets its name from the fact that it’s fangs are relatively large for its body size, and that it is often found in the intertidal zone. Beneath rocks and seaweed, it feeds on barnacles, amphipods, worms, and other marine invertebrates. This centipede can even tolerate extended periods of immersion in salt water!

For this reason, I’ve named ferrugineum the “shore-crawler” rather than the “shore centipede.” Shore-crawler sounds cooler, and cool centipedes get cool names.

Schendyla nemorensis, the clawless soil centipede

This centipede is small and inconspicuous, but one of the most widespread soil centipedes in the world. It exists in Europe as well as much of northern North America, where it is thought to have been introduced by humans, but in fact it may have been here long before us. The name comes from the fact that its last pair of legs lack tarsal claws, for reasons unknown.

Escaryus liber, the Appalachian winter centipede

Like all members of the genus Escaryus, this species is highly cold-tolerant and can remain active through the winter, beneath the frost line. I have examined winter centipedes that were caught in pitfall traps as early as January — my suspicion is that this adaptation allows them to feed on defenseless, hibernating insects, giving them a head start in the coming year.

A soil centipede chomps down on an earthworm ... a little ambitious, perhaps? Photo by Tom Murray.

A soil centipede chomps down on an earthworm … a little ambitious, perhaps? Photo by Tom Murray.

Escaryus urbicus, the short-faced winter centipede

In North America, this is the northernmost representative of Escaryus, and the one you would expect to find in New England. In truth, all winter centipedes have relatively short “faces,” and fangs that don’t extend past the front margin of the head. But only one species could have that common name, so this was it.

Obviously nothing about this list is official — I’d love to hear your thoughts on how the names could be improved. Centipedes, like many invertebrates, are nightmarish to many, fascinating to some, and beautiful to only a few. Perhaps by making them more accessible to the public, we can reveal them for what they truly are: awe-inspiring, magnificent, and ultimately beautiful nightmares.

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.