Caterpillar Q & A: Questions and Answers About Caterpillars
Welcome to Caterpillar Q&A!
Here are answers to the most common questions people are asking about caterpillars.
Where Does the Word "Caterpillar" Come From?
According to Etymology Online, the word "caterpillar" comes from an old French word for "furry cat" -- "chatepelose." It's also possible that in the 15th century the English altered "pelose" to "pillar" to reflect the caterpillar's destructive ability -- "pillar" is a root word of "pillage," meaning to destroy.
Are Caterpillars Insects?
Yes! Caterpillars are insects. They are the immature form of a butterfly or moth. The name of this group is "Lepidoptera," which is Latin for "scaled wings," because their wings are covered with tiny scales that give them their colors. Other groups of insects include beetles, "Coleoptera," and bees, wasps, and ants, "Hymenoptera."
Caterpillars are one of the four stages of Lepidoptera development, a process known as "complete metamorphosis." The adult butterflies or moths mate and lay eggs, which hatch into larvae (caterpillars), which go into "diapause" (cocoons), during which they change into the adult butterfly or moth. Then the process is complete, and ready to begin again.
Each kind of caterpillar turns into a specific kind of butterfly or moth. Matching up the caterpillar with the adult is part of the fun of learning about these insects. For help with matching your caterpillar to the adult, have a look at my CATERPILLAR IDENTIFICATION GUIDE here on Owlcation!
What do Caterpillars Eat?
Almost all caterpillars eat the leaves of plants, and a few can eat enough to damage trees or crops. They have evolved along with their foodplants. Most foodplants don't want to be eaten, so they have chemicals in their leaves to discourage caterpillars. Often these chemicals make them useful to humans as herbs and spices -- basil, for example, or peppermint.
While a butterfly or moth will take nectar from almost any kind of flower, their caterpillars often will only eat one kind of plant. Some caterpillars do eat other insects, but very few.
How Do Caterpillars Eat?
Caterpillars have small but strong jaws that bite like pincers. They get the edge of a leaf between those jaws and just start biting. The tiny bites go into the caterpillar's gut where they're dissolved and turned into energy or fat. Eventually the waste material is ejected as poo (which look like little hand-grenades!).
Can Caterpillars Bite?
In terms of actually biting humans with their mouths, then the answer is simple: No. Their mouth parts are really tiny and designed to eat leaves. Some caterpillars will try to scare you by acting like they're about to bite -- they rear up on their hind feet and might even make a faint clicking sound, but it's all for show. Since moth caterpillars are often larger than butterfly caterpillars, they are often the ones that try to appear scary.
What Caterpillars Sting?
A few moth caterpillars do sting, but no butterfly caterpillars do. In North America, watch out for a caterpillar called "the Asp." It's about an inch long and very furry -- it almost looks like a fancy hair-do. But underneath the fur are sharp spines with a very potent venom, comparable to a wasp sting. Another one to avoid is the caterpillar of the buck moth. This species tends to hang out in groups, and their spines have a toxin that's a bit like stinging nettle. If you brush up against a group these caterpillars, you'll get welts that sting and itch for hours.
There are several other caterpillars that can sting you -- have a look at my article about stinging caterpillars.
The venomous ASP caterpillar
Venomous Buck Moth Caterpillar
Are Caterpillars Dangerous?
Only if you give them a loaded gun! Seriously, the number of caterpillars that are actually dangerous to humans is very small. The vast majority depend on camouflage and hiding to avoid dangerous animals like humans (and birds and lizards).Some have stinging spines, and we will talk about those in a bit. These species can sting you like a bee, but there are only a few that are worth worrying about.
Only moth and not butterfly cateprillars sting, and of those only one is dangerous. There is one caterpillar that actually can kill people, and does -- a few every year. The sting of this South American species, Lonomia obliqua, can cause runaway bleeding throughout the body. If it gets out of control, the victim can die in a few days.
Are Caterpillars Worms?
No. Worms are in the phylum Annelida, which is an entirely different group -- they're not even insects. Sometimes caterpillars are called "worms," but they're very different from the earthworms that you find in the ground, or any other kind of true worm.
Can Caterpillars Swim?
Actually, yes, some can. These are moth caterpillars that live in marshes and in places that have a lot of water, and sometimes flood. These species have adapted to the conditions by evolving the ability to move through the water. They don't exactly swim -- more like wriggle. But they don't drown!
Caterpillar Head Anatomy (Yes, It's Upside Down)
Can Caterpillars See?
Yes, but not well. They have a lot of tiny, very simple eyes -- twelve! -- that are called "ommatidium (om·ma·tid·i·um)." They are really only useful for seeing light and dark, and some movement, to protect them from predators. If a caterpillar senses a threat, it will freeze, and sometimes drop right off the plant. They prefer to take their chances with a fall than with whatever is lurking around them.
Can Caterpillars Hear?
Like all insects, caterpillars do not have ears in the usual sense. But caterpillars do have small antennae, which sense changes in the air, including vibrations. So if you yelled at a caterpillar, it would probably react by freezing, or dropping off the plant. A few butterfly caterpillars try to mimic a snake, so you may see that behavior as well.
Can Caterpillars Turn Into Moths?
Yes, of course. Some turn into moths, and some turn into butterflies, depending on the kind of caterpillar (the "species"). But since there are many more moths than butterflies, the caterpillar that you found will most likely turn into a moth.
Can Caterpillars Lay Eggs?
No, and this is related to the process of metamorphosis. Caterpillars are the larval stage of an adult butterfly or moth, and only the adults mate and lay eggs, not caterpillars. Look at it this way: the caterpillar's only job is to eat and get as fat as possible and store up fat for the adult stage; the adult's only job is to stay alive long enough to mate and lay eggs so the process continues.
" Look at it this way: the caterpillar's only job is to eat and get as fat as possible and store up fat for the adult stage; the adult's only job is to stay ali
How Do Caterpillars Move?
Most caterpillars have six legs in the front, which have tiny claws for gripping and will eventually become the six legs of the adult insect. They also have soft, grippy "prolegs" in the back, which can be quite strong, especially in big caterpillars -- try getting a big caterpillar off of its stick, and you'll see what I mean. Caterpillars use both kinds of legs together to walk around.
Caterpillars in the moth family Geometridae have only two pairs of prolegs in back. They bring these legs on the rear end up to the front, making the body into a loop, and then reach out with the front legs. They look like they're measuring, so they're called inch-worms.
How Most Caterpillars Move
How an Inchworm Moves
How Does a Caterpillars Become A Butterfly or Moth?
This is an excellent question. The process is unbelievably complicated and is the product of millions of years of evolution. Basically, at the end of its eating time, when it's full-grown, the caterpillar sheds its skin for one last time, and this new version of the caterpillar has no arms or legs -- it's basically a pod. This is called a pupa, or a chrysalis. Inside the shell of this pod, the cells rearrange themselves into the form of the butterfly or moth. Then the insect sheds its skin one final time, and out comes the adult, a butterfly or moth with wings.
How Are Caterpillars Born?
Caterpillars are one of four stages in the life of a butterfly or moth. They aren't exactly born -- they hatch out of eggs laid by the adult. The eggs are tiny and unremarkable, and the baby caterpillars are very small and defenseless. There are dozens and dozens of eggs laid by every adult, and most of the baby caterpillars are eaten by birds or ants long before they grow up.
The surviving baby caterpillars eat a lot, and grow fast. About 4 or 5 times during their life they will shed their skin as they outgrow the one they're in. Sometimes the new skin looks a lot different from the old one. When they're done eating they shed their skin again and become a pupa (also called a chrysalis); then that skin splits open and the butterfly comes out.
How Do Caterpillars Make Cocoons?
A cocoon is a protective coat or shelter that keeps the pupa inside it warm and dry, and also out of the reach of birds, ants, and parasites. But a caterpillar will only spin a cocoon if it's a moth, not a butterfly. Butterflies don't spin cocoons, and most moths pupate underground. Only some moths make cocoons.
A cocoon is made from a liquid that comes out of the caterpillar's mouth. When the liquid hits the air, it turns into a thread or fiber; this is the cateprillar's silk. There's a special organ in the caterpillar's "lip," labrum, called a spinneret. This organ spools out the silk and the caterpillar builds the cocoon around itself.
When it's time to hatch, the caterpillar produces a substance that dissolves one end of the cocoon, and the adult moth wriggles out.
When do Caterpillars Make Cocoons?
The most accurate answer to this question is, "When they're good and ready." Caterpillars make their cocoons and chrysalises ("pupate") when they have stored up enough fat for the transition into an adult butterfly or moth. Usually this takes several weeks from the time they hatch out of the egg laid by the adult. Caterpillars can make cocoons at all times of the year, but it is by far most common for them to pupate over the winter. They eat and eat while leaves are out in the summer, spin a cocoon when it gets cold in the winter, and hatch out as an adult in the spring. Then the adults mate, lay eggs, and the process repeats all over again.
Do Caterpillars Predict Winter Weather?
Nope. There's some folklore out there that says the width of the bands on the banded woolly bear, Pyrrharctia isabella, predicts the severity of the coming winter, but there's no research to back this up.
Which Caterpillars Turn Into Butterflies, and Which Caterpillars Turn Into Moths?
Most caterpillars you find will turn into a moth, not a butterfly, because there are about a hundred times more moths than butterflies out there. Caterpillars with "fur," or very large caterpillars with horns or other decorations, are almost always moth caterpillars. Butterfly caterpillars are generally smaller and slimmer than moth caterpillars, and are either smooth or have branched spines all over them.
These are only general rules, though. If you found a caterpillar and you want to know what it is, have a look at my Caterpillar Identification Guide.
When Do Caterpillars Eat?
This is a good question. Whether a moth or a butterfly species, caterpillars eat a lot -- in fact, eating is their only purpose in life, since they're the phase in the cycle of metamorphosis (change in form) that is tasked with accumulating enough fat and calories to produce a big, beautiful adult. But they don't eat all of the time. If you raise a caterpillar, you will notice that they eat at certain times of the day, and rest at other times. Many caterpillars eat at night, when the predators that want to eat them are unable to find them in the dark.
Where Do Caterpillars Live?
Caterpillars live on their food plant, and they basically never leave. They eat and rest, eat and rest, and shed their skin (molt) when the skin they're in gets too tight. Sometimes they come down to earth to prowl around for a good place to make a cocoon, and that's when most people find them.
Which Caterpillars Eat Milkweed?
There are only a few caterpillars that eat milkweed, and this is because the milkweed plant has poisonous, milky sap that it uses to protect itself from things that eat its leaves. But some insects have evolved to deal with the poison. The most famous of these is the monarch butterfly, scientific name Danaus plexippus.
The brightly striped caterpillar of the monarch butterfly eats only milkweed. Sometimes the caterpillar will chew through the main vein of a leaf so there's not as much toxic sap in the part it wants to eat -- apparently evolution is not completely through!
There is another kind of caterpillar that eats milkweed. It's a brightly colored, furry orange and black species that turns into a pretty grey moth -- the milkweed tiger moth.
Will My Caterpillar Turn Into a Monarch Butterfly?
There's only one kind of caterpillar that turns into the monarch butterfly, one of the most beautiful and recognizable of all North American insects. The caterpillar of the monarch eats only milkweed species, and the toxic sap from the milkweed is thought to make the caterpillar and butterfly taste bad to predators.
Which Caterpillars Eat Rose Leaves?
There are a few caterpillars that eat rose, and a couple of the most common ones also sting -- unusual in the caterpillar world. One of them is the io moth, a beautiful species. The caterpillar is green with a red and white line down its side and lots of sharp branched spines. Touch these, and you'll think you've been stung by a bee! The other is known as the "stinging rose caterpillar." It's in the genus Darapsa, a group of moths that all have stinging larvae.
Why do Caterpillars Shed Their Skin?
Caterpillars, like all insects, have an exoskeleton. This means that they have no inner support; it's all supplied by a tough but flexible outer shell. When the insect eats, it grows, and the exoskeleton gets tight. In order to get bigger, the insect has to wriggle out of its old skin to reveal a new one underneath. This new skin is flexible enough to allow the caterpillar to grow larger -- until it reaches the end of the exoskeleton's flexibility, and needs to shed again. At the end of the metamorphosis process, the adult moth or butterfly emerges, and of course it too has an exoskeleton.
What Caterpillars Are Bad, and What Caterpillars Are Good?
Leaving aside the fact that judgements like "bad" and "good" don't apply to caterpillars, which are insentient beings with no moral code, it's true that there are some that are more of a pain to humans than others. Gypsy moth caterpillars, for example, eat a wide variety of trees and can occur in huge numbers, enough to destroy an entire forest. Cabbage white butterfly caterpillars are another persistent pest, on garden plants. There are very few butterfly pest species -- most of them are moths.
No caterpillars are disease vectors, or any real kind of threat to humans. In a way, they're all "good"!
Why Are Caterpillars Hairy?
Look at it this way: Every feature on a caterpillar, from color to shape to "decorations," have evolved over millions of years to help the animal survive and avoid predators. Being hairy is a common strategy among caterpillars (more commonly moth species than butterfly species) for a number of reasons. One of them is to make it hard for little parasitic wasps and flies to land on the caterpillar and lay their eggs. Another is to make the caterpillar a nasty mouth-full for birds, lizards, and other predators.
Every feature on a caterpillar, from color to shape to "decorations," have evolved over millions of years to help the animal survive and avoid predators.
Why Are Caterpillars Green?
The answer to this question goes to a basic need of almost all caterpillars: the need to not be seen by predators. Since they live on plants and eat leaves, caterpillars live in a world of green. It gives them an advantage, from an evolutionary point of view, to blend in with their surroundings. Caterpillars, then, are green because if they were bright orange or blue, predators would have no trouble finding them on their food plant.
Will Caterpillars Eat Each Other?
Surprisingly, the answer is "yes." Some species will eat each other, even though they are technically herbivores. One theory is that they have evolved to limit their own populations when resources are scarce. Eating the surplus population cuts down on competition and provides the survivors with a tasty, nutritious lunch.
One of these species is the cinnabar moth, a beautiful insect that you would never suspect is capable of eating its fellow-caterpillar. Another is the zebra swallowtail butterfly, also a beautiful species.
Will Caterpillars Eat Lettuce?
The answer here here is "yes," but only if it's a species that already eats lettuce. Both moth and butterfly caterpillars can be very picky about the leaves they eat, and very few will actually eat lettuce that you buy at the grocery store. If you found a cateprillar and want to feed it, try a handful of every plant and leaf from the vicinity where you found it. There's a chance that it will eat one of these.
Will Caterpillars Kill Plants or Trees?
Not usually. The vast majority of caterpillars stay in their trees and plants and eat a few leaves without bothering anybody. Once in a while, a few species can get out of hand and due real damage to your garden plants. If this happens, I suggest using diatomaceous earth, which is a completely natural and non-toxic way of controlling insect pests.
Will Caterpillars Eat Aphids and Other Insects?
Very few caterpillars eat aphids. The only common species is a butterfly called the harvester, a very pretty orange-and-black butterfly about an inch across. The caterpillars live on plants where there are aphids, and eat them. This is an excellent source of protein, and the caterpillars grow very quickly. Ladybugs, on the other hand, are voracious aphid-eaters.
There is a kind of moth that lives in Hawaii that has evolved to be a predator. It has sharp legs and snatches up flies and other unsuspecting insects. It's one of the more amazing caterpillars on the planet.
The following resources were used for this guide: