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Did You Know?
The word 'caterpillar' was intended to mean 'hairy like a cat' or '(having) cat hair'. It stems from the Latin words 'cattus', meaning cat, and 'pelose', meaning hairy.
Larvae of butterflies and moths are known as caterpillars. Due to the huge array of butterflies and moths, it is natural that there are several varieties of caterpillars too, making their identification difficult. Larvae of other insects such as beetles and sawflies also resemble caterpillars, but the specific term is only used to denote the larvae of butterflies and moths.

Some caterpillars are covered in poisonous hair or spines. The effects of such stings are similar to those of mild bee and wasp stings, but can also cause serious complications. These caterpillars are found on garden plants, so there is a chance that you have these poisonous caterpillars in your gardens. Therefore, it is imperative that you should be able to identify them correctly.

There are several types of caterpillars, due to the various types of moths and butterflies. Some are smooth while some have hair on them. Some are green, or yellow, red, or black; some have stripes, others have spots, some have horns, and some may even have thorns! Caterpillars are vastly different from each other - there is no way to even distinguish a butterfly larva from a moth larva. Anatomically, though, they all have strong mandibles to chew leaves, up to five pairs of pro-legs, and six simple eyes.

The main distinguishing factor between various caterpillar species is the body color pattern, presence of tapered tips (horns), and the presence of hair. Most caterpillars are colored either in shades that make them harder to spot against their host plant, such as greens and browns, or warning shades such as red, blue, orange, and yellow, that warn potential predators that the caterpillars are poisonous and unpalatable. Caterpillars that are colored distinctively or have large amounts of hair are likely to be poisonous, and should not be handled directly. The sting from some caterpillars can cause nausea, chest ache, digestive dysfunctions, and even death in people sensitive to certain substances. However, horns, if present, are not used as stingers (like in wasps or bees), and are not dangerous to humans. They in fact mimic the actual thorns on a tree, and provide camouflage to the caterpillar.

Caterpillar Identification

Hornworm Caterpillar
Tobacco Hornworm (Manduca sexta)
Description: This is one of the biggest caterpillars, at almost 5 inches in length. They have seven white stripes on each side, and possess a harmless horn at the rear end.

They are found on plants in the Solanaceae family, including tobacco, tomato, peppers, and eggplant.

american dagger moth
American Dagger Moth Acronicta americana
Description: These are about 2 inches long. They have dense yellow setae that are mildly poisonous.

It is found primarily on maple, birch, horse chestnut, hazel, walnut, and oak trees.

citrus swallowtail caterpillar
Citrus Swallowtail (Papilio demodocus)
Description:

These are about 2 inches long. The immature larvae of this species mimic bird droppings in order to escape predators, and they may appear like that to humans as well. Adults have a foul-smelling but nonpoisonous organ called osmeterium, which they may extend defensively.

As the name suggests, these caterpillars are found on citrus trees.

common mormon
Common Mormon (Papilio polytes)
Description:

These measure between 1 and 1.5 inches long. They are spiny and brown when immature, and populate citrus trees, curry leaves, or bael trees.

cloudless sulphur butterfly
Cloudless Sulfur (Phoebis sennae)
Description:

Like many caterpillars on this list, larvae of the cloudless sulfur butterfly are about 2 inches long.

They populate plants such as the partridge pea, clovers, and various legumes. They build a tent in the host tree as a daytime resting place.

buck moth
Buck Moth (Hemileuca maia)
Description:

These are 2 to 2.5 inches long. Buck moth caterpillars are poisonous - their stings can cause not only rashes, but nausea.

They populate oak forests, and pupate underground.

buff tip moth
Buff-tip Moth (Phalero bucephala)
Description:

These can measure up to 3 inches, but are usually smaller than 2.5 inches. These live in a group on trees such as oak, willows, elm, hazel, and rose plants.

Cecropia moth
Cecropia Moth (Hylaphora cecropia)
Description:

Cecropia moth caterpillars are quite large, measuring up to 4.5 inches.

In the initial stages, they are green, but their body may appear black due to the presence of hair. They populate the maple, cherry, and birch trees.

elephant hawkmoth
Elephant Hawk Moth (Deilephila elpenor)
Description:

Elephant hawk moths are named for the caterpillar's superficial resemblance to the shape and color of the elephant's trunk. They have a horn at the rear end, and they adopt a snake-like stance when threatened. They feed on willowherb and bedstraw.

evening brown
Common Evening Brown (Melanitis leda)
Description:

Caterpillars of this butterfly are about 2 inches long. Adults and larvae of this species are considered pests, since they feed on crops such as rice and bamboo, and grasses such as Cynodon.

gulf fritillary butterfly
Passion Butterfly (Agraulis vanilae)
Description:

These caterpillars are about 1.5 inches long―mostly smaller than that. They have soft, nonpoisonous spines. They are not harmful to humans, but are poisonous when eaten, and are thus protected from predators.

These larvae feed exclusively on passionflowers - thus the name of the species.

funerary dagger moth
Funerary Dagger Moth (Acronicta funeralis)
Description:

Funerary dagger moth caterpillars are born brown with white markings on the body.

They are found in alder, apple, dogwood, maple, blueberry, elm, and oak trees.

false unicorn caterpillar
False Unicorn Caterpillar (Schizura ipomoeae)
Description:

These caterpillars measure around 2 inches, and can be mistaken for dried-up leaves.

They feed on morning glory (ipomoea) plants, and beech, oak, and birch trees.

geometrid looper caterpillar
Geometrid Caterpillars (Geometridae family)
Description:

Geometrid caterpillars are known for their typical 'looping' gait. In fact, the name of the family is derived from the gait. Geometrid caterpillars appear to measure (meter) the earth (geo) between each step, hence the name. This behavior occurs because their middle appendages are poorly developed, and they rely on legs and hind prolegs for locomotion.

giant peacock moth
Giant Peacock Moth (Saturnia pyri)
Description:

The giant peacock moth is the largest moth in Europe. It primarily dwells in fruit trees.

gypsy moth
Gypsy Moth (Lymantria dispar dispar)
Description:

These caterpillars range from 2-3.5 inches, and can be fairly easily identified due to the conspicuous arrangement of colored dots on their back. Starting from the head, gypsy moth caterpillars have 5 blue and 6 red spots along their body.

They are found on oak, aspen, apple, willows, pine, and spruce trees.

light knotgrass moth
Light Knotgrass Moth (Acronicta menyanthidis)
Description:

These caterpillars are found on willow and birch trees, and heather and various berries.

hickory horned devil
Hickory Horned Devil (Citheronia regalis)
Description:

These are among the largest caterpillars, measuring just short of 6 inches. In the initial stage, the larvae resemble bird droppings. The seemingly aggressive horns and spines appear on the 6th instar, and are not poisonous to humans.

They are found on ash trees, walnut, hazel, cotton, and honeysuckle.

mourning cloak
Mourning Cloak (Nymphalis antiopa)
Description:

The larvae of this ominously named butterfly are 1-2 inches long. They live in a communally spun web on willow, aspen, and birch trees.

peach blossom moth
Peach Blossom Moth (Thyatira batis)
Description:

This caterpillar is easy to spot due to its bumpy yellow skin, and a characteristic resting posture of raising both its ends in the air.

They feed on plants in the rose family, such as raspberries and blackberries.

peacock butterfly
Peacock Butterfly (Inachis io)
Description:

These caterpillars are about 1.5 inches long, and feed on stinging and other nettles, and the common hop.

pine processionary
Pine Processionary (Thaumetopoea pityocampa)
Description:

These caterpillars are named after their marching behavior of traveling in a single file - procession. They build communal nests in their host trees. They are extremely toxic, and should never be handled.

They are found on pine, cedar, and larch trees.

pipevine swallowtail
Pipevine Swallowtail (Battus philenor)
Description:

As the name suggests, these caterpillars feed almost exclusively on pipevines.

puss caterpillar
Puss Caterpillar (Megalopyge opercularis)
Description:

These seemingly appealing moths are one of the most toxic and dangerous of all caterpillars. Their spines can't be seen at first glance due to their thick 'fur', making them even more dangerous.

These reside in oak and elm trees, citruses, rose, and ivies.

puss moth
Puss Moth (Cerura vinula)
Description:

The puss moth is completely unrelated to the puss caterpillar, though the adults of both species are called 'puss' or 'pussy' moths. The caterpillars of the puss moth are more than 3 inches long. They are not toxic in the same way as other caterpillars, but they may squirt formic acid (found in ant stings) if threatened.

They are found in aspen, willow, and poplar trees.

white admiral
White Admiral (Limenitis arthemis)
Description:

These caterpillars are found in birch, willow, aspen, and bitter cherry trees.

saddleback
Saddleback Caterpillar (Sibine stimulea)
Description:

Named due to their unusual appearance, these caterpillars are a type of slugs (which are actually molluscs). A sting from these caterpillars can be quite painful.

Saddleback caterpillars are found on a wide variety of plants, including the Christmas palm.

silverspotted tiger moth
Silverspotted Tiger Moth (Lophocampa argentata)
Description:

These caterpillars are found on Douglas-fir trees.

six-spot burnet
Six-spot Burnet (Zygaena filipendulae)
Description:

These conspicuous caterpillars are found on clover and birdsfoot trefoil trees.

sycamore moth
Sycamore Moth (Acronicta aceris)
Description:

These striking caterpillars are mildly poisonous. They don't have sharp spines and can be handled, but repeated handling increases the poison dose, and can eventually cause mildly adverse effects.

rusty tussock moth
Rusty Tussock Moth (Orgyia antiqua)
Description:

These caterpillars are less than 2 inches long, and are found in birch, oak, willow, and lime trees.

spurge hawk-moth
Spurge Hawk-moth (Hyles euphorbiae)
Description:

As the name suggests, these moths feed on spurges. In fact they are often used as a natural pesticide to purge out the weed.

spicebush swallowtail
Spicebush Swallowtail (Papilio troilus)
Description:

These ingenious caterpillars construct a shelter for themselves in the host plant. They join two ends of the leaves with their silk, which contracts as it dries, pulling the two ends together.

They are found in spicebush, Joe-Pye weeds, jewelweeds, honeysuckles, thistles, and mimosas.

tomato hornworm
Tomato Hornworm (Manduca Quinquemaculata)
Description:

Tomato hornworms are closely related to the tobacco hornworm (Manduca sexta), and are identified by eight V-shaped markings along their bodies. Like M.sexta, tomato hornworms inhabit plants in the Solanacae family.

eastern tent caterpillar
Eastern Tent Caterpillar (Malacosoma americanum)
Description:

These caterpillars can be easily identified by their communal tent in the host plant, and their defensive behavior. They thrash their front half when agitated, and can squirt cyanide-laden fluids.

They are seen especially in cherry and maple trees.

luna moth caterpillar
Luna Moth (Actias luna)
Description:

These are just less than 3 inches long.

They are found on birch, alder, persimmon, hickory, walnut, moonflower, and tomatoes.

poplar hawk-moth
Poplar Hawk-moth (Laothoe populi)
Description:

These caterpillars are quite stout, and are about 2.5 inches long. They have a green horn at the rear end.

As is obvious from the name, these are found on poplar trees. They are also found in aspens, and infrequently on willows, birches, elms, and oaks.

mullein moth
Mullein Moth (Cuculia verbasi)
Description:

This moth is notorious as a pest. The caterpillars are about 2 inches long.

They feed on mulleins and figworts.

Caterpillars are fascinating to observe, annoying when in your home, and deadly if carelessly handled. It's best to keep it at arm's length, though it is certainly not necessary to kill any that you find in your home. Like any other creature, it is more scared of you than you are of it. Just drop it outside, and it won't bother you any more.