Tag Archives: insect

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.

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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.

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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).

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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.

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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.

Silver and Green

by Joseph DeSisto

Sunlight in the western U.S. can be intense, and all the more so when it catches the shimmering green carapace of a jewel scarab:

A Beyer's jewel scarab from Arizona. Photo by Joseph DeSisto.

A Beyer’s jewel scarab from Arizona. Photo by Joseph DeSisto.

The regal purple legs of this beetle identify it as Beyer’s jewel scarab (Chrysina beyeri). Beyer’s jewel scarabs spend most of their lives as white grubs in rotting logs, where they slowly eat their way through the wood. When they finally emerge as adult beetles, they eat oak leaves.

Although nearly a hundred jewel scarab species are found in Mexico and Central America, only four are known from the U.S.A., all in the southeastern portion of the country. Probably the most visually stunning is the so-called glorious jewel scarab (Chrysina gloriosa), with a lime-green exoskeleton sporting thick stripes of metallic silver.

The glorious jewel scarab, also from Arizona. Photo by Joseph DeSisto.

The glorious jewel scarab, also from Arizona. Photo by Joseph DeSisto.

There is something truly awe-inspiring about a beetle in which you can see your own reflection. We know that, of course, the glorious jewel scarab is not beautiful for our own gratification, but what adaptive purpose could metallic stripes possibly fulfill?

There are likely two. First, the glorious jewel scarab feeds on the leaves of juniper trees, which are common in the beetle’s high elevation habitats in Arizona and Texas. Juniper trees have tiny leaves along narrow branches, and thin strips of sun can create a shimmering effect at the right time of day. The beetle’s shining armor may actually serve as camouflage, by mimicking the narrow rays of sunlight that flicker through the trees.

A glorious jewel scarab on its host, juniper. Photo by Robert Potts, licensed under CC BY-NC-SA 3.0.

A glorious jewel scarab on its host, juniper. Photo by Robert Potts, licensed under CC BY-NC-SA 3.0.

Another Arizona insect uses the same trick. The royal moth’s caterpillar (Sphingicampa) is large and green, with a red stripe on each side and metallic spines jutting out of its back. Yet on their host plants, these caterpillars are well camouflaged. How? Because the plants they live on (locust, acacia, and others) all have small leaves with tiny spaces between them. The spines on royal caterpillars mimic the spaces between the leaves, and the light that flows through them.

A Sphingicampa caterpillar, showing off its metallic spines. Photo by Joseph DeSisto.

A Sphingicampa caterpillar, showing off its metallic spines. Photo by Joseph DeSisto.

The other reason for metallic strips is less obvious. It turns out that jewel and a few other scarab beetles can be so shiny because their exoskeletons reflect a unique kind of light, called circularly polarized light. To understand that, we need to understand a bit of physics.

What we call light is actually the product of tiny packets of energy called photons, travelling through space at the speed of … light. Photons travel in waves, undulating up and down or side to side. Normally, each photon has a wave pointed in its own direction, but sometimes, all the waves are oriented the same way. In other words, all the waves are on the same plane:

When light is polarized, all photons have wavelengths with the same orientation. Figure in public domain.

When light is polarized, all photons have wavelengths with the same orientation. The red wave shows the path of photons in an example. Figure in public domain.

If all the waves are on the same plane, the light is said to be polarized. Polarized light is fairly common in nature — although humans cannot identify polarized light, many insects such as bees use it to orient themselves with respect to the sun. This allows them to navigate between flowers, and to and from their hives.

Circularly polarized light, on the other hand, is extremely rare. In this situation, waves are still on the same plane as each other, but the plane rotates. If you could see the photons as they traveled directly towards you, it would look like a single photon is moving in a spiral, but in fact many photons are moving together, each at slightly an angle to its neighbor:

In circularly polarized light, the plane on which the waves are travelling rotates. Figure in public domain.

In circularly polarized light, the plane on which the waves are travelling rotates. Figure in public domain.

I won’t belabor this — physics is not my strong suit and I would rather omit details than risk getting things wrong. The point is, it takes a very special and rare kind of surface to reflect light in this way — the surface of a jewel scarab.

That’s pretty cool by itself, but it also happens that the same beetles are one of the few animals that can see circularly polarized light. There are lenses that allow us to see the same light, and if we look at a glorious jewel scarab through one of those lenses, it will appear not green and silver, but black (Sharma et al. 2009).

This can help otherwise well-camouflaged jewel scarabs find mates. Experiments with glorious jewel scarabs have shown that they are attracted to and will fly towards circular polarized light (Brady and Cummings 2010). Closely related, but less flashy beetles show no such preference. So while a predator looks at a beetle-filled juniper tree and sees nothing but leaves and shimmering sunlight, beetles can easily spot each other as big, black, radiant spots in a green world.

The Beyer's jewel scarab. Photo by Robert Potts, licensed under CC BY-NC-SA 3.0.

The Beyer’s jewel scarab. Photo by Robert Potts, licensed under CC BY-NC-SA 3.0.

Cited:

Brady P. and M. Cummings. 2010. Differential response to circularly polarized light by the jewel scarab beetle Chrysina gloriosa. The American Naturalist 175(5): 614-620.

Vivek S., M. Crne, J.O. Park, and M. Srinivasarao. 2009. Structural origin of circularly polarized iridescence in jeweled beetles. Science 325: 449-451.

Living Illusions

by Joseph DeSisto

Good camouflage requires more than just color. Millions of years of natural selection have favored birds that can easily identify a brown moth on a brown background, but some species are a little more sophisticated. Lappet moths hide on tree bark – their odd shape, combined with mottled color, helps break up their outline, so visual predators such as birds have a hard time recognizing them as moths.

A lappet moth (Phyllodesma americana) from Arkansas. Photo by Marvin Smith, licensed under CC BY-ND-NC 1.0.

A lappet moth (Phyllodesma americana) from Arkansas. Photo by Marvin Smith, licensed under CC BY-ND-NC 1.0.

These moths lay their eggs on trees including birch, oak, poplar, willow, and many others. The caterpillars munch on leaves by night, hiding on twigs and bark by day. They are also well-hidden, but because they have to be able to live on a variety of different trees, each of which has a differently-colored bark, lappet caterpillars don’t have a color that matches a particular background. Instead they, like their parent moths, have bodies with distorted outlines, specifically a lateral fringe of long hairs.

On bark, this helps a caterpillar “merge” with the bark on which it rests. On a twig, maybe not so much:

A resting lappet caterpillar on one of its favorite hosts, scrub oak. Photo by Joseph DeSisto.

A resting lappet caterpillar on one of its favorite hosts, scrub oak. Photo by Joseph DeSisto.

Animals that depend on camouflage have to stay very still to avoid detection, but if they are spotted, staying still quickly becomes futile. Many animals use color to startle predators as a backup plan, the best-known example being the red-eyed tree frog. At rest, the frogs appear a solid leafy-green, but if disturbed, they quickly open their eyes. The sudden appearance of two giant, bright red eyes can be enough to startle a predator, which might give the frog time enough to make a hasty escape.

The iconic red-eyed tree frog (Agalychnis callidryas). Photo by Carey James Balboa, in public domain.

The iconic red-eyed tree frog (Agalychnis callidryas). Photo by Carey James Balboa, in public domain.

Lappet caterpillars have a similar but more elaborate trick. If a potential predator (or human finger) brushes against a caterpillar, it first flexes its body so the hairs on its back part. This reveals two striking, blood-red bands, a warning this caterpillar might be toxic.

Photo by Joseph DeSisto.

The lappet caterpillar has only to flex its body to reveal these striking bands. Photo by Joseph DeSisto.

Let’s say this doesn’t work, and the bird isn’t intimidated. If a bird’s beak (or my tweezers) pinches the caterpillar, it bends its head back over its body, revealing legs surrounded by pitch-black spots:

Photo by Joseph DeSisto.

This caterpillar doesn’t like me very much. Photo by Joseph DeSisto.

Still not startled? The lappet caterpillar has one last show. In desperation, it falls from its perch in the trees and, on hitting the ground, flops upside-down, revealing a bright yellow-and-black belly:

Photo by Joseph DeSisto.

Yellow and black are universal warning signs — many toxic animals share these colors. Photo by Joseph DeSisto.

If this doesn’t work, the caterpillar is pretty much toast. For all its show, the lappet caterpillar isn’t poisonous – at worst, some of its hairs are mildly irritating to the skin. Like the red-eyed tree frog, it relies entirely on visual illusions to ward off predators. It sounds risky, but it’s worked at least some of the time for millions of years.

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.

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.

The Fork-tailed Dragons

by Joseph DeSisto

Meet Furcula borealis, the caterpillar of the white furcula moth:

Furcula cinerea, the caterpillar of a medium-sized, gray moth. Photo by Joseph DeSisto.

Furcula borealis, the white furcula caterpillar. Photo by Joseph DeSisto.

It’s a weird-looking caterpillar already, but even weirder when viewed head-on:

The fork-tailed dragon caterpillar, Furcula borealis. Photo by Joseph DeSisto.

The fork-tailed dragon caterpillar, Furcula borealis. Photo by Joseph DeSisto.

Like all insects, caterpillars have only six legs, and these are located near the front of the body, just behind the head. The sticky, climbing appendages along the rest of the trunk are not true legs but “prolegs,” which are lost during metamorphosis. In Furcula caterpillars (and the related Cerura, shown below), the last pair of prolegs are modified into long, rigid “tails.”

Cerura scitiscripta, showing six true legs near the head (upper left), four typical prolegs on the trunk, and the special modified pair of prolegs at the rear of the body -- the forked

Cerura scitiscripta, showing six true legs near the head (upper left), four typical prolegs on the trunk, and the special modified pair of prolegs at the rear of the body — the forked “tail.” Photo by Joseph DeSisto.

The furcula moths belong to the strange and beautiful family Notodontidae. These are sometimes called prominent moths, despite mostly being brown, gray, or some combination thereof. Recall, however, that in my last post about caterpillars I referred to notodontid caterpillars as the dragon caterpillars. Furcula, then, are unofficially dubbed the fork-tailed dragon caterpillars.

In case you’re wondering what F. borealis looks like as a moth, here’s an example specimen:

The white furcula moth, Furcula borealis. Photo by Tom Murray, used with permission.

The white furcula moth, Furcula borealis. Photo by Tom Murray, used with permission.

So what is the forked tail for? To find out, we simply tap our little dragon on the head. This is what happens:

Furcula borealis. Photo by Joseph DeSisto.

Furcula borealis, beginning its display. Photo by Joseph DeSisto.

Bright red tentacles begin to emerge from the  modified prolegs. In less than a second they are fully everted:

Don't mess with the fork-tailed dragon! Photo by Joseph DeSisto.

Furcula borealis, tentacles emerging from modified prolegs. Photo by Joseph DeSisto.

The fork-tailed dragon then waves these tentacles about, and even attempts to rub them onto the offending party (i.e., my finger). The “strike” reminds me of a scorpion trying to sting, if scorpions dressed up as clowns and went to birthday parties. After tapping me, the tentacles disappear as quickly as they emerged, while the caterpillar tucks its head and braces itself for another attack.

Furcula borealis. Photo by Joseph DeSisto.

Furcula borealis. Photo by Joseph DeSisto.

In a less dramatic fashion, many insects use eversible organs to rub toxins on their predators. Rove beetles are an example — this explains the way many of them run, with abdomens held high in the air like scorpions. If you grab one, it will use its flexible abdomen to rub a cocktail of nasty chemicals on you, some of which can cause blistering. But in Furcula and Cerura caterpillars, the tentacle-rubbing is actually a harmless show designed to scare off predators. I must admit, were I a foraging bird, I would think twice about attacking a caterpillar with such a bizarre and intimidating display.

And yet, in an ironic twist, these caterpillars are not harmless. If sufficiently disturbed, they can fire off a burst of formic acid — the stuff fire ants sting you with — from glands behind the head. In F. borealis, these are stored in spiky, poisonous-looking projections:

If you're mean enough, this caterpillar might just spray formic acid at you. Photo by Joseph DeSisto.

If you’re mean enough, this caterpillar might just spray formic acid at you. Photo by Joseph DeSisto.

Don’t mess with the fork-tailed dragons!

Pictures of Cats

by Joseph DeSisto

By cats I mean caterpillars, of course.

This summer, in addition to working on centipedes, I have a job working in the lab of Dr. David Wagner, an entomologist here at UConn. He studies caterpillars, which means I get to watch hundreds of different species go through metamorphosis. It’s pretty great. Today I’ll share some of my favorites — the caterpillars I give a few extra leaves every day, just because I love them.

But first, a quick lesson on caterpillar anatomy. Here’s Catocala amica, in profile:

Catocala amica, the caterpillar of a large and beautiful underwing moth. Photo by Joseph DeSisto.

Catocala amica, the caterpillar of a large and beautiful underwing moth. Photo by Joseph DeSisto.

Although caterpillars look like they have lots of legs, they actually only have six tiny ones at the front of the body, like all insects. The larger, pad-shaped structures are prolegs, and they will disappear during metamorphosis. Most caterpillars, including this Catocala, have five pairs of prolegs, but others such as inchworms (family Geometridae) have fewer.

Now let’s look at the head:

Another view of Catocala amica. Photo by Joseph DeSisto.

Another view of Catocala amica. Photo by Joseph DeSisto.

The bulbous portions of the head are not eyes — the simple eyes, or stemmata, are clustered in the lower corners of the caterpillar’s face. The head is so large because it holds all the muscles needed for what the caterpillar spends virtually all its time doing: eating. The antennae are small and project down, toward the leaf.

In case you’re curious, Catocala amica turns into a large moth, affectionately known as the friendly underwing:

The friendly underwing, same species as the caterpillar above. Photo by Ilona L., licensed under CC BY-ND-NC 1.0.

The friendly underwing, same species as the caterpillar above. Photo by Ilona L., licensed under CC BY-ND-NC 1.0.

Because a lot of caterpillars turn into butterflies, it might be easy to assume that caterpillars are the “ugly ducklings” of the insect world, a kind of lowly purgatory for insects before they transform into something beautiful. But in many cases, such as in the family Notodontidae, the caterpillar is by far the more visually stunning. Here, for example, is Notodonta torva the moth, pinned and spread as a museum specimen:

An adult Notodonta torva, a European moth. Photo by M. Virtala, in public domain.

An adult Notodonta torva, a European moth. Photo by M. Virtala, in public domain.

But in the Wagner lab, this is what I get to feed and clean up after, every day until it pupates:

Notodonta torva, as a caterpillar. Photo by Joseph DeSisto.

Notodonta torva, as a caterpillar. Photo by Joseph DeSisto.

Notodontids have some of the wildest-looking caterpillars, with strange outgrowths and protuberances giving them a dragon-like appearance. Here’s another notodontid we’re rearing, in the genus Schizura (I don’t know the species):

Schizura, species unknown (to me). Photo by Joseph DeSisto.

Schizura, species unknown (to me). Photo by Joseph DeSisto.

Schizura caterpillars are fairly opportunistic — they’ll eat almost any woody plant, unlike many caterpillars which have very specific diets (think of the monarch, which eats only milkweed).

Another Schizura, munching away. Photo by Joseph DeSisto.

Another Schizura, munching away. Photo by Joseph DeSisto.

Notodontids are awesome. In the future I think I’ll refer to them as dragon caterpillars. That isn’t their real common name — I just made it up. But of course, all common names are just names people make up. If they make their subjects sound cool, it’s nobody’s loss.

That’s it for caterpillars today, but you can bet there will be more posts about caterpillars in the future.

Although I took the caterpillar pictures in this post, thanks are owed to Dr. David Wagner, who is the proprietor of both the camera and the caterpillars. You can learn more about his work on his lab website, here.

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.

Tiny Dragons in Bromeliad Pools

by Joseph DeSisto

In the last week, three amazing new Central American invertebrates were described, in two publications. These species, one dragonfly and two oligochaete worms, are interesting primarily because of where they were found: in the water-holding urn of bromeliad plants.

Bromeliads are flowering plants in the family Bromeliaceae, and include more than 3,000 mostly tropical species. The family includes such disparate species as the ground-dwelling pineapple (Ananas comosus) and the epiphytic Spanish “moss” (Tillandsia usneoides). Many epiphytic bromeliads, those species that live on the surfaces of trees, are shaped so as to hold pools of water between their leaves.

A water-holding bromeliad plant in the genus Werauhia. Photo by Dick Culbert, licensed under CC BY 2.0.

A water-holding bromeliad plant in the genus Werauhia. Photo by Dick Culbert, licensed under CC BY 2.0.

This makes them important components of the rainforest canopy community: although the rainforest floor may be perpetually moist, higher up the air dries, and permanent sources of standing water may be rare. As a result, many species dwell in the bromeliads’ urns, ranging from microscopic ostracods to salamanders, tree frogs, and even a species of Jamaican crab.

To this list Haber et al. (2015) add a new species of dragonfly, a member of the widespread family Libellulidae. Although adult dragonflies are aerial predators, their larvae are aquatic, and so their parents lay eggs in bromeliad pools. Of course, the larvae are themselves predatory, so what are they eating? Apparently, lots of other species live in bromeliad pools, including mosquito larvae, which provide the dragons with plenty to eat.

A second paper, Schmelz et al. (2015) includes a review of the microdrile oligochaete (tiny annelid) worms found in bromeliad pools in a Honduran cloud forest. It turns out that in this forest, at least six microscopic annelid worms are found in bromeliads, among them two new species in the family Enchytraeidae. This family also includes a variety of soil-dwelling species, which behave essentially like tiny earthworms, but in bromeliad pools they make their living by feeding on decaying plant matter that somehow makes its way into the water.

From worms and crabs to dragonflies and frogs, the miniature ecosystem is diverse and vibrant, and clearly there is much still to be discovered.

Cited:

Haber, W.A., D.L. Wagner, and C. de la Rosa. 2015. A new species of Erythrodiplax breeding in bromeliads in Costa Rica (Odonata: Libellulidae). Zootaxa 3947(3): 386-396.

Schmelz, R.M., M. Jocque, and R. Collado. 2015. Microdrile Oligochaeta in bromeliad pools of a Honduran cloud forest. Zootaxa 3947(4): 508-526.