Caterpillars are the larval forms of butterflies or moths. They look like earthworms, centipedes, myriopods or even the larvae of other insects; however, you can recognize them due to some features of your body as well as your habits. There are several resources that can help you with this identification process.
Method 1 of 2: Identifying Caterpillars in General
Step 1. Understand the basic anatomy of the caterpillar
Although it may look like an earthworm, it can be divided into the same three parts as the insect it will change into:
- Head. The head has two sets of six simple eyes and sharp, powerful jaws capable of tearing leaves into small pieces. There is a spinneret on its lower lip that produces the silk used to support the caterpillar and spin the cocoon created during metamorphosis.
- Chest. The chest has six legs, used to hold food. These, called "true legs", will remain in the insect's body even after metamorphosis.
- Abdomen. The abdomen of a caterpillar is longer than that of an adult insect. It has eight temporary legs, called “false legs” and which are attached to the center. Another pair of false legs, called "anals", are attached to the back of the abdomen. They help the animal to climb branches and the like.
- The entire body is covered with small hairs (arrows) that give the animal tact. In some species, these hairs can be quite striking, giving the caterpillar a “hairy” appearance.
- In contrast, centipedes have a pair of legs in each segment of their body, ranging from 15 to 117 (always in an odd number), while myriopods have two pairs of legs in each segment, ranging from 10 to 180 (40 to 750 legs). The larvae of other insects, such as beetle elaterids, have only six legs.
Step 2. Familiarize yourself with the caterpillar's general habitat
It is often found on or near the plants they consume. Some species devour other caterpillars. Many species are colored so that they can blend in with the plant they inhabit, using it as camouflage.
- Other species are colored to look like predators such as snakes – using, for example, markings that make them look bigger or colors that make them look “unpalatable”.
- Some caterpillars are colored; many of these consume the toxins found in ingested plants, which can poison their predators. The monarch butterfly is famous for doing this – both as a caterpillar and as an adult.
- Centipedes and myriopods, in contrast, are found under rocks, logs, decaying wood, leaves and other places where they can accumulate and retain moisture.
Step 3. See how the caterpillar moves
These animals are very slow and move in an “undulating” manner, similar to earthworms. Its rear segments contract, which transports blood to the front segments and “extends” the caterpillar. Its front legs firm when the muscles contract, bringing the hind legs closer together.
Centipedes, in contrast, move faster using their many legs
Step 4. Examine the caterpillar closely
Some caterpillars have a Y-shaped gland in their necks, which gives them a pungent odor that drives away predators.
Method 2 of 2: Identifying Specific Caterpillar Species
Step 1. Examine the caterpillar marks
If their coloring is intended to disguise them from predators or to “inform” everyone that they are full of toxins, most species can be identified through this aspect. Some examples include:
- Monarch butterfly caterpillars are yellow with black and white spots.
- The forest tent caterpillars have black and blue bodies, in addition to white keyhole markings on the back.
- East tent caterpillars also have black and blue markings on their bodies, but they have a solid white stripe in the center of their back.
- Gypsy moth caterpillars have black bodies with red and blue dots down the centers of their backs.
- There is, for example, a species of caterpillar whose body is pale green, with white and green markings and a protrusion similar to a horn.
- Some caterpillars adapt their color according to the period of the year. The moth species “Nemoria arizonaria” resembles the oak tree blossom and is found during spring and on the leaves of small trees during autumn. Both the spring and autumn “versions” of this caterpillar turn into emerald green moths after metamorphosis.
Step 2. Examine what the caterpillar eats
In many cases, you will be able to identify a particular caterpillar by the type of plant on which it is found.
- Monarch butterfly caterpillars are found under the leaves of sawdust (their sap has a toxin that makes the caterpillar and its adult version poisonous to predators).
- The forest tent caterpillars have black and blue bodies, in addition to white keyhole markings on the back. They can be found on the leaves of ash, oak, maple trees etc.
- East tent caterpillars also have black and blue markings on their bodies, but they have a solid white stripe in the center of their back. They feed on the leaves of apple and cherry trees.
- Gypsy moth caterpillars have black bodies with red and blue dots down the centers of their backs. They feed primarily on oak leaves and other hardwoods, but usually ingest sugar maple leaves.
- Other species of caterpillars also have their own specific “diets”.
Step 3. Consult a field guide
If you are not familiar with the species of caterpillars where you live or encounter a different animal during a trip, you can consult this guide.
- It is possible to find guides made for children.
- Probably the best ones are made for adults and are in English (like Thomas J. Allen's “Caterpillars in the Field and Garden” and David's “A Field Guide to Caterpillars of Butterflies and Moths in Britain and Europe” J. Carter).
Step 4. Search the internet
There are several reference sites that can be useful for identification – and can be accessed from your personal computer or even from cell phones and tablets, as long as there is an internet connection.
- Regional guides such as the “Caterpillars of Pacific Northwest Forests and Woodlands” and the US “Caterpillars of Eastern Forests” are good options for consultation. Offer images and the like.
- You can find additional features, including mobile and tablet apps, on the internet.
- You can find several pages in Portuguese on the subject.
- Another alternative is to search wikiHow.
- A magnifying glass can be useful in helping to identify some of the characteristics of a caterpillar. You can also learn some technical terms for the anatomy and habitat of these animals (in addition to those presented in this article) so that you can use them effectively.
- If you have the time and the patience, you can “raise” a caterpillar into its adult form. Only a small number of moth and butterfly larvae are known today; therefore, having images of both its larval and adult forms is interesting.