Tag Archives: venomous

North America’s Big Five Centipedes

When Halloween comes around, snakes and spiders tend to steal the show. Yet centipedes, in my experience, tend to evoke even stronger reactions from people — I have met many entomologists who would happily handle a tarantula but recoil in horror when faced with a giant centipede.

In the United States there are five species of giant centipedes in the family Scolopendridae. Today, in the spirit of Halloween, I give you the Big Five: where they are found, what they do, and why I love them.

Blue Tree Centipede (Hemiscolopendra marginata)

The blue tree centipede. Photo by Sharon Moorman.

The blue tree centipede. Photo by Sharon Moorman.

This is the smallest of the five, seldom exceeding 3 inches, but still the largest centipede throughout most of its range. It is found through much of the East, from Ohio and Pennsylvania south to Florida and west to eastern Texas. Tree centipedes are also found in Mexico south to the Yucatan Peninsula. As the name suggests, the tree centipede is often an attractive blue-green, with yellow legs and orange fangs. The brightness of the color depends on the location, however, and some are paler than others.

The blue tree centipede is a habitat specialist, living under the bark of rotting trees, often before they have toppled to the ground. I have had the best luck finding them under the bark of pine logs. Because they are such good climbers, they occasionally wind up in buildings where they can cause quite a scare.

Bites from tree centipedes are painful but not much worse than a bee sting. They use their venom, as all centipedes do, to kill prey. Because they prefer to live in rotten pine logs, they may specialize in hunting beetle grubs that eat rotting wood. Like most centipedes, however, data on their feeding habits is severely lacking.

Green-striped Centipede (Scolopendra viridis)

The green-striped centipede is larger, reaching 6 inches or so, and usually pale yellow with a thick green or black stripe running down the back. Other patterns exist, however, and in parts of their range this species can appear more like a tree centipede or a tiger centipede (#4). These are adaptable centipedes, found from Florida west to Arizona, but don’t seem to venture further north than South Carolina.

The green-striped centipede. Photo by Jeff Hollenbeck, licensed under CC BY-ND-NC 1.0.

The green-striped centipede. Photo by Jeff Hollenbeck, licensed under CC BY-ND-NC 1.0.

Green-striped centipedes can live in a variety of habitats but they seem to prefer sandy forests. In Florida they can be found in scrub habitat, but like all centipedes they are not well-adapted to drought, and must stay moist by hiding underground or in rotting logs during the day.

Caribbean Giant Centipede (Scolopendra alternans)

The Caribbean giant is the only one of the Five with the russet-brown, mono-chromatic appearance of a “typical” centipede. It is probably our largest species, with a length easily exceeding 8 inches. However, the Caribbean giant is, as you might have guessed, a tropical centipede, and in the U.S. it lives only in southern Florida. It requires humid habitats, and the best place to find them is in and around the Everglades, in Dade and Monroe Counties.

A certain foreign species, the Vietnamese giant (Scolopendra subspinipes), is easily confused with the Caribbean giant at first glance. That wouldn’t be a concern, except that the Vietnamese giant has already become invasive in Hawaii and — this is just my speculating — is likely to become established in the Everglades at some point in the future. Because it is so large, often exceeding 10 inches, the Vietnamese giant is sometimes sold in the pet trade. Bites from either species are not deadly, but extremely painful.

Tiger Centipede (Scolopendra polymorpha)

A tiger centipede from Arizona. Photo by Sue Carnahan, licensed under CC BY-ND-NC 1.0.

A tiger centipede from Arizona. Photo by Sue Carnahan, licensed under CC BY-ND-NC 1.0.

Like the green-striped centipede, the tiger is a 6-inch-long animal found in a variety of habitats. Unlike the green-striped, this is a strictly western species, found from Idaho south through California into Mexico, and east all the way to Missouri. Its name comes from its color pattern: each segment is orange or yellow with a narrow, dark band.

Giant centipedes often move faster by undulating in a snake-like fashion, taking advantage of their long and muscular bodies. When a tiger centipede does this, the bands appear to “flicker,” rather like the brightly-banded milk snake and coral snake. This can make the centipede more difficult to track visually, and hence more difficult for a bird or mouse to grab.

Tiger centipedes, like their namesake, are voracious predators. They have been seen taking down prey much larger than themselves, including geckos and praying mantises. In turn, tiger centipedes are prey for scorpions, spiders, snakes, and many other predators.

A tiger centipede, fallen prey to a scorpion. Photo by Jasper Nance, licensed under CC BY-NC-ND 2.0.

A tiger centipede, fallen prey to a scorpion. Photo by Jasper Nance, licensed under CC BY-NC-ND 2.0.

Centipedes are adapted to moving fast, and their exoskeletons are thin and flexible. The drawback is that they dehydrate very easily. Although tiger centipedes are found in deserts, they still have to remain underground most of the time to conserve moisture.

Giant Desert Centipede (Scolopendra heros)

If you’ve ever seen centipedes used in a horror movie, they were probably heros*. They are big, reaching 8 inches or more. They are also brightly colored in black and orange — perfect for Halloween!

The Arizona form of the giant desert centipede. Photo by Aaron Goodwin, licensed under CC BY-ND-NC 1.0.

The Arizona form of the giant desert centipede. Photo by Aaron Goodwin, licensed under CC BY-ND-NC 1.0.

Heros are found in the desert Southwest, and color patterns vary by location. In eastern Texas and Oklahoma, they are typically jet-black with a bright orange head and yellow legs. In Arizona (above) they are usually red, with the first and last segments black. In New Mexico and western Texas the pattern is orange with black bands, much like a tiger centipede.

A giant desert centipede. Photo from NMNH Insect Zoo, licensed under CC BY-NC 2.0.

A giant desert centipede. Photo from NMNH Insect Zoo, licensed under CC BY-NC 2.0.

Why have black on just the head and the last segment? This an example of automimicry, in which one part of an animal’s body mimics the other. In this case, the tail-end of the giant desert centipede mimics its head-end. When faced with a giant centipede, predators usually attack the head, hoping to avoid a painful bite. If a predator gets confused, however, and attacks the tail instead, an unpleasant surprise awaits when the true head whips around to greet its attacker.

Centipedes, giant and otherwise, are pretty scary, and I never begrudge people who are afraid of them. Still, centipedes are amazing animals and if you see one, I encourage you to take a closer look. It will teach you, if nothing else, that just because an animal is frightening does not mean it can’t be beautiful.

*There is a centipede in one of the Human Centipede movies. People often tell me this after I tell them I study centipedes, so let me clarify a few things: I don’t know what kind of centipede the bad guy has for a pet. Not because I couldn’t identify it, but because I have never watched those movies and never will. I also don’t want to hear you describe your favorite scene with as many details as possible. Thank you.

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 Mountain King

by Joseph DeSisto

During my trip to Arizona, I saw tarantulas, scorpions, black widows, giant centipedes, lizards, and way too many insects to name here. What I didn’t see a lot of were snakes — in fact I only saw two, but those two snakes were the most beautiful I had ever seen.

The first was in Sierra Vista where, after a long day of beating bushes for caterpillars, we pulled into a driveway to find one of the most stunning animals on earth: the Arizona mountain kingsnake.

An Arizona mountain kingnake, held by Benedict Gagliardi. Photo by Joseph DeSisto.

An Arizona mountain kingnake, held by Benedict Gagliardi. Photo by Joseph DeSisto.

The Arizona mountain kingsnake (Lampropeltis pyromelana) and its cousin, the California mountain kingsnake (L. zonata), are some of the most sought-after snakes by North American reptile-lovers. Both are incredibly beautiful, but not especially common, and they prefer high-elevation habitats that aren’t always very accessible to naturalists. Mountain kingsnakes are secretive, spending most of their time underground. They seldom bask in the sun like garter snakes or rattlesnakes, instead emerging only to track hunt their lizard and rodent prey, which they kill by constriction.

The Arizona mountain kingsnake, from Sierra Vista. Photo by Joseph DeSisto.

The Arizona mountain kingsnake, from Sierra Vista. Photo by Joseph DeSisto.

The bright red and yellow bands are warning to predators. Snake-eating birds and mammals might easily confuse the kingsnake with the extremely venomous Sonoran coralsnake, which is also found in Arizona but prefers the lower-elevation desert scrub habitats, rather than the upland pine forests favored by the mountain kingsnake.

I am on a lucky streak when it comes to snakes. I don’t see very many, but the ones I do see are special enough to make my friends jealous. During a May trip to the Appalachians, I saw only five snakes, but two of those were corn snakes and two more were eastern worm snakes. Despite both of these being great finds, I left the South feeling a bit slighted, since what I really wanted to see was a venomous snake, a timber rattlesnake or copperhead. I had never seen a venomous snake in the wild before, so when I decided to go to Arizona, known for being rattlesnake country, I was ready.

The other mountain kingsnake, L. zonata from California. Photo by James Maughn, licensed under CC BY-NC 3.0.

The other mountain kingsnake, L. zonata from California. Photo by James Maughn, licensed under CC BY-NC 3.0.

We spent a few days in Sierra Vista collecting caterpillars and setting up lights at night to attract moths and other insect curiosities. Pat Sullivan, a beetle expert who lives in the area, had several pet rattlesnakes and was eager to show me a rock pile he had set up on his property as snake habitat.

The night he took me to the rock pile, just a few yellow scales caught the beam from my flashlight. I could see perhaps an inch of snake that looped out from under a rock, and I wanted to flip the rock to see more. I also, however, didn’t want to put my hands right next to a rattlesnake who might not be as sociable as I was. So I left the snake be, and returned to the light where moths and beetles kept me busy for the rest of the evening.

The last morning before we left Sierra Vista, I returned to the rock pile. After a few minutes of leaning over for a good angle, I realized the snake was in exactly the same position as before, only a few scales visible. In daylight those few scales were truly beautiful — they yellow and tan color revealed this was a black-tailed rattlesnake (Crotalus molossus), one of the prettiest rattlesnakes around. Pat got a long stick and, very carefully, flipped the rock over:

This is what I saw -- half a black-tailed rattlesnake. Photo by Joseph DeSisto.

Half a black-tailed rattlesnake. Photo by Joseph DeSisto.

The snake made no attempt to strike or even rattle. It simply slid beneath the rock pile with the grace of an animal that knows it can hurt you, and knows that you know it can hurt you. In the end I only had a few seconds to see less than half of a rattlesnake, but I’ll take it. I saw my first and, to date, only venomous snake in the wild, and it was one of the most beautiful creatures I’ve ever had the pleasure of meeting.

How Poisons Work: Tetrodotoxin

by Joseph DeSisto

This is the first of a series of short articles, each featuring a different type of poison or venom used by animals.

Poisons and venoms are some of the most complex substances in nature, often containing hundreds of different chemicals, each with a particular purpose. As technology advances, scientists have begun to look at some of these chemicals, usually proteins, and try to figure out what they do.

The deadly southern blue-ringed octopus (Hapalochlaena maculosa). Photo by Bernard Dupont, licensed under CC BY-SA 2.0.

The deadly southern blue-ringed octopus (Hapalochlaena maculosa). Photo by Bernard Dupont, licensed under CC BY-SA 2.0.

In some cases, the results give us a new perspective on an animal’s biology: rattlesnake venom, for example, contains a unique protein that allows the snake to track its prey after the initial strike. In other cases, we discover potentially useful surprises: giant centipede venom contains a single protein that inhibits pain in mice, using the same chemistry as morphine, but with greater efficiency. However, regardless of whether the results are useful to us, studying nature’s chemical weapons gives us a whole new appreciation and understanding of the creatures that wield them.

Tetrodotoxin is the poison of choice for a variety of animals, especially in the ocean. These include blue-ringed octopuses, cone snails, moon snails, certain angelfish, some ribbon worms, a handful of amphibians, and the puffer/triggerfish order Tetraodontiformes, for whom the toxin is named. Many of the animals that use tetrodotoxin are brightly colored, a warning to passers-by. Would-be predators, save the immune and the unlucky, heed this warning well.

An inflated pufferfish (Diodon holocanthus). Photo from Williams et al. (2010), licensed under CC BY 2.5.

An inflated pufferfish (Diodon holocanthus). Photo from Williams et al. (2010), licensed under CC BY 2.5.

Tetrodotoxin, sometimes abbreviated TTX, is a complex molecule that prevents its victims’ nerves from functioning properly. This eventually leads to paralysis, and death comes when the muscles that control breathing no longer receive signals from the nervous system. Basically, you suffocate. Humans can get TTX poisoning when they eat improperly-prepared pufferfish, but stings from blue-ringed octopuses and cone snails (both from the southwestern Pacific) are also a possibility if you are foolish enough to pick them up.

Although many animals use TTX, none of them actually manufacture the toxin themselves. Instead bacteria generate the toxin, to their host’s benefit. In exchange, the bacteria are allowed to live safely within their host’s body — the bacterium Pseudoalteromonas tetraodonis, for example, makes its home within the livers and skins of pufferfish.

A toxic moon snail (Naticarius orientalis) from East Timor. Photo by Nick Hobgood, licensed under CC BY-SA 3.0.

A toxic moon snail (Naticarius orientalis) from East Timor. Photo by Nick Hobgood, licensed under CC BY-SA 3.0.

The rough-skinned newt, from British Colombia and the western United States, has the bacteria needed to make TTX for itself — as a result, this newt has few natural predators. Two animals, however, have managed to work around and even benefit from the rough-skinned newt’s toxins, all without toxin-producing bacteria of their own.

The only animal capable of eating an adult rough-skinned newt is the garter snake. After ingesting the newt, any other predator would almost certainly die, but a few populations of garter snakes have evolved an immunity to TTX. What’s more, the snakes are able to sequester the toxins within their own bodies, so that the garter snakes themselves become poisonous (Williams et al. 2004).

The extremely toxic rough-skinned newt (Taricha granulosa). Photo by Rennett Stowe, licensed under CC BY 2.0.

The extremely toxic rough-skinned newt (Taricha granulosa). Photo by Rennett Stowe, licensed under CC BY 2.0.

Although many snakes inject toxins with their fangs, and so are venomous, garter snakes that eat rough-skinned newts are the only snakes that can truly be considered poisonous. The difference is that venomous animals have to inject their poisons into predators or prey, via fangs or stingers, while poisonous animals are laced with their chemical weapons and are dangerous to eat.

The other TTX-robber is, unexpectedly, a caddisfly. Caddisflies are insects whose larvae resemble caterpillars, but live underwater and surround themselves with cases made from pebbles, twigs, and other debris. Most are scavengers, eating decomposing plant matter and tiny invertebrates, while the flying adults are short-lived and do not feed.

A Limnephilus caddisfly larva, in its protective case made of twigs. Photo by Tom Murray, used with permission.

A Limnephilus caddisfly larva, in its protective case made of twigs. Photo by Tom Murray, used with permission.

A few predatory species in the genus Limnephilus, however, have developed an unusual appetite for rough-skinned newt eggs, which also develop in the water. These eggs are loaded with TTX, and the toxin-resistant Limnephilus larvae manage to eat so many that even the caddisfly adults are toxic (Gall et al. 2012).

Even though many marine invertebrates contain tetrodotoxin, we still don’t know how many contain the bacteria that make it, versus how many, like the caddisfly, “steal” the toxin from their TTX-laced prey. Certain sea slugs, for example, are often washed on shore where they are eaten by beach-combing scavengers such as dogs. In New Zealand, several dogs have died after eating sea slugs that contained TTX (McNabb et al. 2009), and in Argentina, a population of the same slugs appears to have become invasive (Farias et al. 2015). Yet we still do not know whether they have their own TTX-generating bacteria.

A toxic sea slug, Pleurobranchaea meckelii. Photo from Wägele and Klussmann-Kolb (2005), licensed under CC BY 2.0.

A toxic sea slug, Pleurobranchaea meckelii. Photo from Wägele and Klussmann-Kolb (2005), licensed under CC BY 2.0.

Experiments have shown that certain populations of sea slugs have TTX, while others do not (Khor et al. 2014) — just like the garter snakes of North America. Does this mean the sea slugs are obtaining TTX from some unknown, toxic prey item? The same researchers conducted a survey of all the marine invertebrates that these slugs might be eating, testing everything for TTX. The only positive result was a toxic species of sand dollar, but the sand dollars didn’t produce nearly enough TTX to explain the huge amounts found in sea slugs.

Ignorance has consequences, and there is still plenty of exploring left to do. The slugs may in fact make tetrodotoxin themselves (using bacteria). A more enticing possibility, and just as likely, is that there are still more toxic animals on the sea floor, waiting to be discovered.

One of the very first articles I wrote for this site featured the same sea slugs mentioned in this one, but that was when my only readers were a few sympathetic family members. If you’re curious about sea slugs, and/or you want to know the difference between a nudibranch and a pleurobranch, you can read that article here.

I also recently wrote about how rattlesnake’s use their venom to track once-bitten prey (mentioned in the second paragraph of this article). To learn more about that, click here. It’s amazing, I promise.

Cited:

Farias, N.E., S. Obenat, and A.B. Goya. 2015. Outbreaks of a neurotoxic side-gilled sea slug (Pleurobranchaea sp.) in Argentinian coasts. New Zealand Journal of Zoology, published online: DOI: 10.1080/ 03014223.2014.990045.

Gall, B.G., A.N. Stokes, S.S. French, E.D. Brodie III, and E.D. Brodie Jr. 2012. Predatory caddisfly larvae sequester tetrodotoxin from their prey, eggs of the rough-skinned newt (Taricha granulosa). Journal of Chemical Ecology 38(11): 1351-1357.

Khor, S., S.A. Wood, L. Salvitti, D.I. Taylor, J. Adamson, P. McNabb, and S.C. Cary. 2014. Investigating diet as the source of tetrodotoxin in Pleurobranchaea maculata. Marine Drugs 12(1): 1-16.

McNabb, P., L. Mackenzie, A. Selwood, L. Rhodes, D. Taylor, and C. Cornelison. 2009. Review of tetrodotoxins in the sea slug Pleurobranchaea maculata and coincidence of dog deaths along Auckland Beaches. Prepared by Cawthron Institute for the Auckland Regional Council Technical Report 2009/108.

Williams, B.L., E.D. Brodie Jr., and E.D. Brodie III. 2004. A resistant predator and its toxic prey: persistence of newt toxin leads to poisonous (not venomous) snakes. Journal of Chemical Ecology 30(10): 1901-1919.

Things that Sting

by Joseph DeSisto

I love scorpions. They’re fast, predatory, venomous … really, everything you could want in animal. So in Arizona, while I was supposed to be collecting caterpillars, I occasionally took a “scorpion break,” flipping rocks and digging in the sand.

We spent a day collecting along Montezuma Pass, a mountain road that winds through Coronado National Forest. Towards the base of the mountain, where pine forest gives way to grassy scrub, I struck gold. Scorpions were everywhere.

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

The striped devil scorpion, ready for action.. Photo by Joseph DeSisto.

By far the most common was the striped devil scorpion (Vaejovis spinigerus), which is found in dry, lowland habitats through much of Arizona and New Mexico. These are big scorpions, approaching 3 inches in length, with a sting that is painful but not medically threatening (except in the case of an extreme allergic reaction).

The biggest scorpions were the mothers, carrying babies on their backs. Although striped devil scorpions can reproduce by mating, if the pickings are slim, a female can also produce young asexually, without mating.

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

A mother striped devil scorpion, carrying young. Photo by Joseph DeSisto.

So I wandered through the sun-baked grass, flipping rocks and scrutinizing the ground. I was so focused on my scorpions that I stumbled into one of the strangest things I had ever seen. In the middle of the field was a circular clearing, about six feet across, where no plants grew. There was only sand and, on closer inspection, ants.

A harvester ant "arena." Photo by Joseph DeSisto.

A harvester ant “sand garden.” Photo by Joseph DeSisto.

The ants in question were harvester ants (genus Pogonomyrmex). Harvester ants are scavengers that subsist mostly on seeds. I watched as teams of ants brought back seeds and the occasional dead insect from the surrounding grassland, stuffing them into small entrances that led to a vast network of underground tunnels and storage chambers.

I’d heard that harvester ants were defensive and had powerful stings, but these ones seemed comfortable with me strolling across their sand garden, and even kneeling to get a closer look. To see if their reputation was justified, I grabbed one and pressed its abdomen against the soft skin of my wrist.

A team of harvester ants carting a stink bug back to their nest. Photo by Joseph DeSisto.

A team of harvester ants carting a dead stink bug back to their nest. Photo by Joseph DeSisto.

Sure enough, it stung me and administered a healthy dose of venom. The result was a sharp pain, like being stuck with a pin, and this pain grew over the next 30 minutes or so. Ultimately, however, I was disappointed — it didn’t hurt that much. Were these ants, which seemed to have such a well protected territory, aggressive at all?

Perhaps the ants simply weren’t frightened by me. I decided to give them a real threat, and see how they reacted. So I flipped a few rocks, grabbed the first scorpion I could find, and dropped it into the center of the sand garden.

The response was immediate and severe. The moment the scorpion hit the ground, a party of three ants grabbed onto it with their large jaws and began to sting. As they did so, they released a pheromone, a chemical alarm signal that brought dozens more ants to their aid. Within seconds, the scorpi0n was surrounded.

A scorpion after being killed by an army of harvester ants. Photo by Joseph DeSisto.

A scorpion after being killed by an army of harvester ants. Photo by Joseph DeSisto.

A few minutes passed, and the ants piled on. The scorpion quickly expired, as sting after sting injected deadly venom. Still, the ants held guard over the invader for several hours, as if to make sure it didn’t come back to life.

The same scorpion, long after death, still guarded by a team of ants. Photo by Joseph DeSisto.

The same scorpion, long after death, still guarded by a team of ants. Photo by Joseph DeSisto.

Harvester ants clearly don’t like scorpions, which makes sense. It’s likely that, if caught alone, a single ant would be easy prey for a 3-inch-long scorpion. But a scorpion, no matter how large, would be unwise to enter a harvester ant colony’s sand garden. Given how quickly and violently the ants responded, I thought that perhaps I too should give them a wide berth. Striped devil scorpions might be large, intimidating, and ready to sting, but they are by far not the fiercest or most venomous animals of Montezuma Pass.

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.