Caterpillars of Northern Illinois

Here's one of the nicest looking caterpillars in the Northern Illinois area, the caterpillar of the brown hooded owlet moth. As with most moths, this caterpillar is usually much better looking than the adult. Sometimes the bright colors are a warning to birds that the caterpillar is toxic because of the plants it's been eating.

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A close relative of the brown hooded owlet moth, but with a very different color scheme. This is one of the few caterpillars which isn't just named after the moth or butterfly it turns into, but has its own common name, The Asteroid. This name comes from its Latin or scientific name, Cucullia asteroides, which might have been given to it because of the long, fiery streaks along its body. The white ovals on its body are the spiracles it uses to breath; insects don't have lungs, instead they draw air in through holes which lead into finer and finer tubes within the body, distributing oxygen in that way. This isn't as efficient as lungs, which is one thing limiting the maximum size of insects.

The Asteroid comes in a surprising number of different color variations. As well as the green model above, here's a purple one...

...and here's a nice rich brown one. As you can see, all of them have yellow stripes on top and along the sides, all have white spiracles and all have some pattern of black pin-striping, but other than that anything goes!

The white-marked tussock moth caterpillar is one of the best looking in the tussock moth family, the red head, yellow stripes, white tufts and prominent tail all add to its appearance, and the two bright red glands on its back are striking too, like little red lights. It's supposed to be a very common caterpillar, though somehow I only saw it once; the female moth is flightless and since it doesn't have any wings it hardly looks like a moth at all. I photographed a similar looking caterpillar called the painted pine moth in Vietnam and it turns out they both belong to the same genus!

Birds eat a lot of caterpillars, but there are other dangers too. Some broods have 90% or more of their number parasitized by wasps, which lay their eggs in or on the caterpillar, which is then eaten alive by the larvae. Poisonous hairs and bad taste can be very effective at keeping birds away, but they don't work as well on wasps, which is why some caterpillars, including this yellow-based tussock moth, are covered with hairs intended to keep female wasps and their ovipositors at arm's length.

Here's another tussock moth, the banded tussock moth, which is somehow even hairier than the yellow-based tussock moth. The word "tussock" in its name refers to the clumps of hairs which distinguish this family. The protection seems to work very well in this case, because the banded tussock moth caterpillar often feeds and rests on the top surfaces of leaves during the daytime.

This milkweed tussock moth caterpillar looks more like a poodle than most people's idea of a caterpillar! Milkweed is also what monarch butterflies eat, but there's little risk of competition here because monarchs prefer younger shoots while milkweed tussock moth caterpillars are happy to eat older, tougher foliage. That's just as well, because female milkweed tussock moths lay large groups of eggs, and the caterpillars are gregarious and can strip whole milkweed patches bare.

This wee beastie certainly has plenty of hair tussocks, but I wouldn't bet any money that it's a tussock moth.

Actually I don't know what this is, but since I photographed it in southern Wisconsin I suspect that my inability to identify it is some sort of instant karma brought about by my attempt to sneak it onto a page of northern Illinois caterpillars.

The Virginia ctenucha belongs to a family called tiger moths, which are related to the tussock moths and are quite common all around the world. It lives in grassland, in this case at Chain O' Lakes state park. The caterpillar has a simple elegance and the adult moth is quite attractive, too.

The woolly bear or black-ended bear rivals the monarch butterfly caterpillar as the most well-known caterpillar in America.

It's not an especially attractive caterpillar, so it might seem strange that it's so famous, however the reason is that it's the subject of a rural legend. According to this old wives' tale, the length of the orange band predicts the severity of the upcoming winter - a short band means a cold winter.

The reality is that the orange band varies in length from caterpillar to caterpillar, and even as a single caterpillar grows, each "instar" that emerges after the old skin is shed has more orange in it. There are even different "color morphs" of the woolly bear, some of which are completely orange.

One reason that the woolly bear is associated with winter is that it can often be seen walking around on the ground about the time of the first frosts. Unlike most other caterpillars, they don't overwinter as eggs or cocoons, instead they spend this difficult time in caterpillar form under leaf litter, feeding again in spring before building a cocoon.

Like the Virginia ctenucha, the woolly bear is a member of the tiger moth family. In this case, the adult moth is a fairly dull creature called the Isabella tiger moth.

The boldly colored and patterned larva of the monarch butterfly is perhaps the most famous caterpillar in the world. It's a popular subject for school projects, since its entire life-cycle completes very quickly, sometimes in less than 30 days. It's also good for this purpose because of its extraordinary feats of migration, flying for thousands of miles from North America to their winter roosts in Mexico.

The monarch is colored like this as a warning that it's poisonous; it stores the heart toxins from its milkweed host within its body, and they're even carried forward into the chrysalis and the adult butterfly. This particular monarch caterpillar has something else pretty nasty, in the form of a pellet of poop between its hind claspers. Of course professional lepidopterists (people who study butterflies and moths for a living) would never call this poop, instead they'd use the proper term for it, which is "frass". See, you learned something new today, so now all you have to do is show off this wonderful bit of hard-won knowledge to your friends, family and acquaintances!

What does this viceroy caterpillar have in common with the monarch? Almost nothing, except that the adult viceroy is a very good mimic of the adult monarch. As you can see, though, the young don't look even faintly similar. The young viceroy is a bird-dropping mimic, a good ploy, since birds aren't big on eating their own droppings. I think that this must either be an unusual color phase or a fairly late instar, because other photos of this species have a sickly green color in place of the red, which gives them much more of the appearance of a bird-dropping.

Here's the larva of one of America's most beautiful butterflies, the common buckeye. The caterpillar isn't bad either; if viewed with the light at the correct angle those spines along its back are dark metallic blue. Despite their vicious appearance, the spines aren't harmful to the touch, which is just as well because even its head is covered in them.

The larva of another of America's most common and attractive butterflies, the red admiral. I'm cheating a bit on this one, since it's another one I photographed in southern Wisconsin rather than northern Illinois. I noticed a curled up nettle leaf and when I unrolled it here was this spiky guy sheltering inside, with a head every bit as spiny as the buckeye.

This eastern comma might not be pretty, but it has a good chance of winning the "spiniest caterpillar of northern Illinois" contest. It gets its name from the comma shape on the back of the hind wing of the adult butterfly.

If you think that "comma" is a strange name for a butterfly then how about "question mark"?

This is the young of the "question mark" butterfly, named not for the shape you see it forming here, but for a white question mark shape on the wing of the adult.

Both the comma and the question mark belong to the "anglewing" family, the wings are indeed angular rather than rounded, with the undersides patterned much like tree bark to enable the butterfly to easily hide in the forest.

If "comma" and "question mark" are strange, then how about "great spangled fritillary"? This one was wandering around in the daytime across a road in Chain O' Lakes state park, which is highly unusual, since they're normally nocturnal and stay hidden. They have a very strange early life, in the fall the females lay around 2000 eggs each, which is an extraordinarily high number for a butterfly, the eggs hatch two to three weeks later, but the first instars don't eat anything for the next seven or eight months. When they do eat they won't touch anything except for violet plants.

From a group of caterpillars which are ugly, spiky and harmless to one which is soft, very attractive and quite possibly the most feared and hated caterpillar species in America!

And here's the reason why - although it's cute by itself, with up to 350 brothers and sisters all voraciously eating away they can strip whole trees at a rapid rate. They construct a giant silk "tent" for themselves in the fork of a tree, which protects them from predators and acts as a hothouse when it's cold.

Henry's marsh moth photographed at Volo Bog. This species folds a blade of grass over to create a triangular area within which it builds its cocoon.

This beautiful smeared dagger moth caterpillar was hanging out on a reed beside the boardwalk that goes through Volo bog.

This is another of those relatively few caterpillars in America which have a common name - the smartweed caterpillar. The name is only somewhat appropriate, since it eats many different types of plants and not just smartweed.

The smartweed caterpillar is highly variable in color, here's one without even a trace of red. In all cases they have an interrupted yellow stripe below white spiracles, and a few very long hairs sticking out from the head and the tail.

The young of the funerary dagger moth is another which has a common name - the paddle caterpillar. It's pretty obvious how it got its name, with those unusual projections out of the top of each body segment. The appearance of the yellow humps on its back has been compared to upside-down cowry shells.

I didn't realize it when I took this photograph, but this is a very rare caterpillar - some American lepidopterists go their whole career without ever seeing one.

This is the young of the black swallowtail butterfly, which likes to eat members of the carrot family including celery, dill and parsley. Many swallowtail butterfly caterpillars have attractive colors and patterns, and most of them have a bad-smelling, orange-colored, y-shaped "osmetrium" just behind the head which is turned inside out when the caterpillar feels threatened.

This certainly looks like another swallowtail caterpillar, but I can't tell which one. Although the pattern is very similar to the black swallowtail, this one has small spines.

This polyphemus moth caterpillar I found at Dead River is large, up to three inches, it belongs to a group called the giant silkworms. The adult polyphemus moth is large and fairly attractive, though it's not in the same league as some of the other giant silkworm moths such as the luna moth, cecropia moth or promethea moth. An attempt was made to create a silk industry from these American species, but it didn't work out because the Asian silkworm does a better job.

You don't need me to tell you that the polyphemus moth looks pretty alien, with its head partly drawn into the first section of its body, and that crazy looking face and claws. Their behavior can be pretty strange too, they sometimes make a snapping noise with their mandibles and other polyphemus moth caterpillars in the area will join in.

See the Butterflies of Northern Illinois and the Butterflies of Vietnam.