How to Identify a Caterpillar
Understand a caterpillar’s basic anatomy., Familiarize yourself with a caterpillar’s general habitat., Note how the caterpillar moves., Get a whiff of it., Look at the caterpillar’s markings., Look at what the caterpillar eats., Consult a field...
Step-by-Step Guide
-
Step 1: Understand a caterpillar’s basic anatomy.
Although a caterpillar’s body may look like that of a worm, it can be divided into the same three parts as the insect it will become as an adult:
Head.
The head features two sets of 6 simple eyes and sharp, powerful jaws that can tear up the leaves it eats into small, edible pieces.
A spinneret on the lower lip exudes a silk that can be used to support the caterpillar and to spin the cocoon it enters to metamorphose into an adult.Thorax.
The thorax sports 6 of the caterpillar’s legs, using them to hold onto its food.These legs, or true legs, will remain with the insect after it undergoes metamorphosis into its adult form.
Abdomen.
The abdomen of a caterpillar is longer than that of the insect’s adult form.
Eight temporary legs, called prolegs, are attached to the center of its abdomen.
Another pair of prolegs, or anal prolegs, are attached to the rear of its abdomen.These prolegs help it to climb.The entire body is covered with tiny hairs (setae) that provide it with a sense of touch.
In some species, these can be quite pronounced, giving the caterpillar a woolly appearance.
In contrast, centipedes have one pair of legs for each body segment, with anywhere from 15 to 177 body segments (always an odd number), while millipedes have two pair of legs for each body segment, with anywhere from 10 to 180 segments (40 to 750 legs).Larvae of other insects, such as the wireworm larvae of beetles, have only six legs. -
Step 2: Familiarize yourself with a caterpillar’s general habitat.
Caterpillars are normally found on or around the plants they eat. (A few caterpillars, such as the zebra swallowtail butterfly larva, eat other caterpillars.) Many species are colored to blend in with the plants they inhabit, often hiding to further the disguise.Other species are colored to resemble predators like snakes, often with eye-like markings to make them look bigger, or are colored to match inedible things, such as the tiger swallowtail butterfly larva’s coloration resembling bird excrement.
Some caterpillars are brightly colored; many of these consume the toxins found in the plants they eat, which can poison the predators that eat them.
The monarch butterfly is best known for this, as both a caterpillar and an adult. .Centipedes and millipedes, in contrast, are found under rocks, logs, rotting wood, fallen leaves, or other places that attract and retain moisture., Caterpillars move slowly, in a rippling or undulating fashion similar to that of an earthworm.
Their rear segments contract, which pushes blood into their forward segments, lengthening them.
Their forward legs seize their position as the segment muscles contract, bringing the rear segments forward.Centipedes, in contrast, move very quickly using their many legs. ., Some caterpillars, such as the zebra swallowtail, have a Y-shaped gland (osmeterium) on their neck that gives off a pungent odor to ward off predators. , Whether their coloration is to disguise them from predators or to advertise they are full of toxins, most caterpillar species can be distinguished by their distinctive markings.
Some examples of distinctive colorations are these:
Monarch butterfly caterpillars are yellow with black and white bands.
Forest tent caterpillars have fuzzy black and blue bodies with white markings shaped like keyholes running down the centers of their backs.
Eastern tent caterpillars also have fuzzy black and blue bodies, but they bear a solid white stripe down the centers of their backs.
Gypsy moth caterpillars have fuzzy black bodies with red and blue spots running down the centers of their backs.Tomato hornworms are pale green caterpillars with white and green markings and a protrusion resembling a horn.Some caterpillars adapt their coloring according to the time of year.
The species ‘’Nemoria arizonaria’’ resembles the flower of the oak tree it is found in during the spring and the leaves of the small tree during the fall. (Both the spring and fall versions of the caterpillar metamorphose into a bright emerald-green moth.) , Many times you can identify a given caterpillar species by what kind of plant it is found on.
Monarch butterfly caterpillars are found on the underside of the leaves of milkweed plants.(Milkweed sap contains a toxin that makes the larvae and adults poisonous to predators.) Forest tent caterpillars have fuzzy black and blue bodies with white markings shaped like keyholes running down the centers of their backs.
They can be found on the leaves of ash, oak, quaking aspen and sugar maple trees, among others.
Eastern tent caterpillars also have fuzzy black and blue bodies, but they bear a solid white stripe down the centers of their backs.
They feed on the leaves of apple and cherry trees.
Gypsy moth caterpillars have fuzzy black bodies with red and blue spots running down the centers of their backs.
They feed primarily on the leaves of oaks and other hardwoods, but may sometimes feed on sugar maple leaves.Tomato hornworms are pale green caterpillars with white and green markings and a protrusion resembling a horn.
They are found on the leaves and stems of tomato plants., If you’re not familiar with the caterpillar species in your area, or encounter a different species when traveling, you can consult a field guide.
Two good guides for children are the ‘’Peterson First Guide to Caterpillars’’ by Amy Wright and ‘’Golden Guide to Butterflies and Moths’’ by Robert T.
Mitchell.Guides for adults include Thomas J.
Allen’s ‘’Caterpillars in the Field and Garden’’ and David J.
Carter’s ‘’A Field Guide to Caterpillars of Butterflies and Moths in Britain and Europe.’’, A number of online reference guides to various caterpillar species are available for you to access from your home computer or mobile device with an active Internet connection.
The Caterpillar Guide of Discover Life’s IDnature series (http://www.discoverlife.org/mp/20q?guide=Caterpillars) helps you identify a caterpillar species by selecting the caterpillar’s main body color, pattern, hair density, and distinct features.
The Butterflies and Moths of North America’s website (http://www.butterfliesandmoths.org/identify) features an image gallery from which you can identify the species of caterpillar you’re looking at.
You can also submit your sighting and a photograph to have one of the group’s regional coordinators identify it, but to do so, you have to register with the site.
Regional guides such as the United States Geological Survey’s Northern Prairie Wildlife Research Center’s ‘’Caterpillars of Pacific Northwest Forests and Woodlands’’ and ‘’Caterpillars of Eastern Forests’’ are structured like the printed field guides they were adapted from.
The Pacific Northwest guide allows users to identify a caterpillar based on how it looks, while the Eastern Forest guides groups caterpillars by family..
You can find additional resources, including mobile applications, by performing an Internet search. -
Step 3: Note how the caterpillar moves.
-
Step 4: Get a whiff of it.
-
Step 5: Look at the caterpillar’s markings.
-
Step 6: Look at what the caterpillar eats.
-
Step 7: Consult a field guide.
-
Step 8: Search online.
Detailed Guide
Although a caterpillar’s body may look like that of a worm, it can be divided into the same three parts as the insect it will become as an adult:
Head.
The head features two sets of 6 simple eyes and sharp, powerful jaws that can tear up the leaves it eats into small, edible pieces.
A spinneret on the lower lip exudes a silk that can be used to support the caterpillar and to spin the cocoon it enters to metamorphose into an adult.Thorax.
The thorax sports 6 of the caterpillar’s legs, using them to hold onto its food.These legs, or true legs, will remain with the insect after it undergoes metamorphosis into its adult form.
Abdomen.
The abdomen of a caterpillar is longer than that of the insect’s adult form.
Eight temporary legs, called prolegs, are attached to the center of its abdomen.
Another pair of prolegs, or anal prolegs, are attached to the rear of its abdomen.These prolegs help it to climb.The entire body is covered with tiny hairs (setae) that provide it with a sense of touch.
In some species, these can be quite pronounced, giving the caterpillar a woolly appearance.
In contrast, centipedes have one pair of legs for each body segment, with anywhere from 15 to 177 body segments (always an odd number), while millipedes have two pair of legs for each body segment, with anywhere from 10 to 180 segments (40 to 750 legs).Larvae of other insects, such as the wireworm larvae of beetles, have only six legs.
Caterpillars are normally found on or around the plants they eat. (A few caterpillars, such as the zebra swallowtail butterfly larva, eat other caterpillars.) Many species are colored to blend in with the plants they inhabit, often hiding to further the disguise.Other species are colored to resemble predators like snakes, often with eye-like markings to make them look bigger, or are colored to match inedible things, such as the tiger swallowtail butterfly larva’s coloration resembling bird excrement.
Some caterpillars are brightly colored; many of these consume the toxins found in the plants they eat, which can poison the predators that eat them.
The monarch butterfly is best known for this, as both a caterpillar and an adult. .Centipedes and millipedes, in contrast, are found under rocks, logs, rotting wood, fallen leaves, or other places that attract and retain moisture., Caterpillars move slowly, in a rippling or undulating fashion similar to that of an earthworm.
Their rear segments contract, which pushes blood into their forward segments, lengthening them.
Their forward legs seize their position as the segment muscles contract, bringing the rear segments forward.Centipedes, in contrast, move very quickly using their many legs. ., Some caterpillars, such as the zebra swallowtail, have a Y-shaped gland (osmeterium) on their neck that gives off a pungent odor to ward off predators. , Whether their coloration is to disguise them from predators or to advertise they are full of toxins, most caterpillar species can be distinguished by their distinctive markings.
Some examples of distinctive colorations are these:
Monarch butterfly caterpillars are yellow with black and white bands.
Forest tent caterpillars have fuzzy black and blue bodies with white markings shaped like keyholes running down the centers of their backs.
Eastern tent caterpillars also have fuzzy black and blue bodies, but they bear a solid white stripe down the centers of their backs.
Gypsy moth caterpillars have fuzzy black bodies with red and blue spots running down the centers of their backs.Tomato hornworms are pale green caterpillars with white and green markings and a protrusion resembling a horn.Some caterpillars adapt their coloring according to the time of year.
The species ‘’Nemoria arizonaria’’ resembles the flower of the oak tree it is found in during the spring and the leaves of the small tree during the fall. (Both the spring and fall versions of the caterpillar metamorphose into a bright emerald-green moth.) , Many times you can identify a given caterpillar species by what kind of plant it is found on.
Monarch butterfly caterpillars are found on the underside of the leaves of milkweed plants.(Milkweed sap contains a toxin that makes the larvae and adults poisonous to predators.) Forest tent caterpillars have fuzzy black and blue bodies with white markings shaped like keyholes running down the centers of their backs.
They can be found on the leaves of ash, oak, quaking aspen and sugar maple trees, among others.
Eastern tent caterpillars also have fuzzy black and blue bodies, but they bear a solid white stripe down the centers of their backs.
They feed on the leaves of apple and cherry trees.
Gypsy moth caterpillars have fuzzy black bodies with red and blue spots running down the centers of their backs.
They feed primarily on the leaves of oaks and other hardwoods, but may sometimes feed on sugar maple leaves.Tomato hornworms are pale green caterpillars with white and green markings and a protrusion resembling a horn.
They are found on the leaves and stems of tomato plants., If you’re not familiar with the caterpillar species in your area, or encounter a different species when traveling, you can consult a field guide.
Two good guides for children are the ‘’Peterson First Guide to Caterpillars’’ by Amy Wright and ‘’Golden Guide to Butterflies and Moths’’ by Robert T.
Mitchell.Guides for adults include Thomas J.
Allen’s ‘’Caterpillars in the Field and Garden’’ and David J.
Carter’s ‘’A Field Guide to Caterpillars of Butterflies and Moths in Britain and Europe.’’, A number of online reference guides to various caterpillar species are available for you to access from your home computer or mobile device with an active Internet connection.
The Caterpillar Guide of Discover Life’s IDnature series (http://www.discoverlife.org/mp/20q?guide=Caterpillars) helps you identify a caterpillar species by selecting the caterpillar’s main body color, pattern, hair density, and distinct features.
The Butterflies and Moths of North America’s website (http://www.butterfliesandmoths.org/identify) features an image gallery from which you can identify the species of caterpillar you’re looking at.
You can also submit your sighting and a photograph to have one of the group’s regional coordinators identify it, but to do so, you have to register with the site.
Regional guides such as the United States Geological Survey’s Northern Prairie Wildlife Research Center’s ‘’Caterpillars of Pacific Northwest Forests and Woodlands’’ and ‘’Caterpillars of Eastern Forests’’ are structured like the printed field guides they were adapted from.
The Pacific Northwest guide allows users to identify a caterpillar based on how it looks, while the Eastern Forest guides groups caterpillars by family..
You can find additional resources, including mobile applications, by performing an Internet search.
About the Author
Kevin Lopez
Enthusiastic about teaching practical skills techniques through clear, step-by-step guides.
Rate This Guide
How helpful was this guide? Click to rate: