What Kind of Caterpillar Is This?
"Hey I found a caterpillar!" When I was young, we were always on the lookout for cool insects, especially cool caterpillars. Maybe you just found one and you're looking for a little help with identifying it. If so, you're are in the right place! I have been helping people ID specimens ever since I was a kid. I am always happy to have friends and neighbors bring me insects for identification. Most of the time it's something common yet cool, but once in a while I come across a real puzzler.
This article is intended to help you identify that caterpillar you found crawling across your kitchen floor, driveway, or on the side of your house.
White-Marked Tussock Moth
This cool-looking species can be commonly found on trees in urban areas. They eat almost anything, including decorative hawthorns and acacias, and when they have a population explosion they can strip the leaves off of entire trees. White marked tussock moth caterpillars also have irritating spines that can cause a rash in some people, so handle with care!
The moth that these ones become is fairly plain, and the female doesn't even have wings—just a furry body which never really leaves the cocoon. The males fly to it, they mate, and the female lay a foamy mass of eggs right on the cocoon!
This familiar orange and black caterpillar can often be found hustling across rural roads in late summer. They are a member of the Arctiidae family, which includes tiger moths and some of our most beautiful Lepidoptera. Wooly bears become the isabella tiger moth; the scientific name is Pyrrharctia isabella.
Wooly bears often hibernate over winter under a rock or in a sheltered place. When they spin a cocoon, it includes stiff bristles from their body. Handling a cocoon can give you little slivers, a little like handling fiberglass insulation.
Tomato Horn Worm
The tomato hornworm is a familiar pest of tomato plants throughout North America. These big guys can completely destroy a tomato plant, and they eat both the leaves and the fruit. If something is eating the leaves of your plant down to the stem, and there are big holes being gnawed in the tomatoes, then these big green crawlers are probably to blame. Have a look around the base of the plant for big caterpillar poops—they look a little like hand grenades. If the poops are there, there's no doubt that you have tomato hornworms.
The best way to deal with them is to find them and pick them off by hand. Then you can drop them in a bucket of soapy water to kill them. You won't find every one, but you'll get enough to save your crop.
This cateprillar becomes a big, strong moth known as a hawkmoth. You can raise one or two to adulthood very easily if you're curious. Give them fresh tomato leaves and keep them in tupperware. They'll turn into a brown shiny pupae, then hatch into cool, big moths.
I used to find these crawling on the side of my house. This big green caterpillar has silver strips on its side and red bumps along the body. It eats oak, maple, and willow. They can sometimes be found in late summer, wandering around looking for a place to pupate. They spin oval cocoons, sometimes under your house's eaves or in evergreens near the crop plants.
The adult moths are truly spectacular. They're various shades of soft brown, with a big smokey eyespot on each hindwing. The big single eye gives them their name, polyphemus, which refers to the one-eyed cyclops in The Odyssey.
This pretty green species with false eye-spots turns brown before it forms a chrysalis and turns into the tiger swallowtail, a truly spectacular butterfly with bold yellow and black stripes. I once found a number of these big beauties clustered around an outhouse—and they're also attracted to cigar smoke!
All of the swallowtail butterflies have a red forked organ called an osmeterium that can stick out from behind its head if it feels threatened. The osmeterium looks like a small snake tongue, which might scare off predators. It smells bad too. This defensive organ is unique to the swallowtails.
I have had these pretty green and black caterpillars on my carrots every year since I can remember. Like the above species, this swallowtail has an osmeterium as well. Sometimes known as a parsley worm, the black swallowtail caterpillar can eat a number of different umbelliferae species.
The black swallowtail butterfly is gorgeous, flying among gardens and forest edges in mid-summer. It's one of the most common swallowtail butterflies in North America.
One of the best known butterflies in North America, the monarch is famous for its astounding migration across half a continent during the winter to the piney mountains in Mexico. That feat is enough to make the monarch impressive, but there is more. The monarch caterpillar eats only milkweed plants, which have a toxic white sap that flows when a leaf or branch is broken, giving the plant its common name. It's thought that this species takes on the poison of the milkweed's leaves, which protects it from predators; since the big orange butterfly is toxic, other butterflies try to copy it. This is called mimicry and there are many species that look like the monarch for this reason.
This cool looking caterpillar belongs to the sphinx moth group, which includes the tomato horn worm and many other big species. The false eyes on the head may scare away predators, and it acts like a small snake when threatened. The moths are sleek and streamlined, and look like a little jet plane.
Although this species is common only in the south, it has been spreading north recently, showing up as far north as Michigan and New York.
This caterpillar is huge. It eats maples and sycamores, and when it leaves the tree to look for a place to pupate, you may find it roaming around outside. Despite its horns and size, it's completely harmless.
The moth that this big crawler becomes, Eacles imperialis, is known as the imperial moth. It's mottled orange and yellow, and looks a lot like a big fallen leaf. This example of camouflage shows effective cryptic coloring.
This species is a kind of cutworm, a group that feed on low plants, often eating through the stem near the ground and cutting down the plant like a lawn mower. Noctua pronuba was unknown in North America up until the 1970s, when it was introduced on the east coast. Within a few decades it had spread all the way across the continent, feeding on all kinds of plants.
This is a pretty moth that has quite a variety of colors—the forewings, or primaries, may be dark brown or light tan. The underwings are bright yellow which is how it got its name in Britain, "the large yellow underwing."
Another large horn worm, Sphinx rustica has become quite common across the south and parts of the west. The caterpillar is gorgeous, but the moth is really cool-looking; big and thick-bodied, with rich rusty brown wings with black and white markings.
American Dagger Moth
The American dagger moth is a member of a group, the Acronictinae, that has interesting caterpillars and fairly drab adult moths. Other members of this group, such as the funerary dagger moth, feature caterpillars that are truly weird looking. I always thought it odd that cool caterpillars have boring moths, but the pattern is often repeated across the Insect world.
This one can sting, and I remember finding that out by accident when I was a boy. I handled one of these cool looking larvae, and wound up with a nasty, stinging rash. Saddlebacks belong to the Limacodidae family, which also includes other stinging specimens of various interesting designs.
These ones turn into a pretty brown moth with a variety of green and orange patches on the upper wings.
This is a stinging species that sometimes drops out of trees and onto people. The sting of the asp, which is also know as the puss caterpillar, can be quite severe. Pain can radiate into other limbs and can last for a day or more. These are more common in the south, where their appearance—and their stings—are often well known.
The Banded Sphinx
This gorgeous specimen can be fairly common in Florida and other southern states, though this species is essentially tropical, ranging through the Caribbean and into Central and South America. It becomes a truly spectacular moth. This caterpillar is big and bright enough that people often find it on branches of their preferred food plant, water primrose.