Caterpillars are the larval stage of butterflies and moths. They have a head and thoracic and abdominal segments. Caterpillar thoracic regions have three pairs of legs; the abdominal area has between three and five pairs of prolegs. To identify a particular caterpillar species, observe the size, colour, stripe or spot patterns, hair coverage and distinguishing features, such as spines or horns. If you are trying to identify a brown, fuzzy caterpillar, the hairiest family of caterpillars is Arctiidae, the tiger moth family, although not all members are brown. A brown, fuzzy caterpillar may also belong to the tussock moth family Lymantriidae and possibly families Lycaenidae and Limacodidae -- the hairstreak and slug caterpillar families, respectively.
Take a picture of the caterpillar that you can refer to when you get home.
Write down all observations including length using a ruler, all colour patterns including spots and stripes, whether the hair is in tufts or densely covers the caterpillar body and distinguishing features such as nobs, horns on the head, body shape and spiky spines. Use a hand lens to help you make precise observations.
Identify the brown, fuzzy caterpillar according to length. For example, the salt marsh caterpillar (Estigmene acrea) is up to 2 inches long, whereas the fall webworm (Hyphantria cunea) is usually less than an inch long.
Identify the brown, fuzzy caterpillar by its colouring and pattern. For example, the banded woollybear (Pyrrharctia isabella) has a reddish-brown core with black ends. The streaked tussock moth caterpillar (Dasychira obliquata) has horizontal, black bands covered with light brown hairs.
Identify the brown, fuzzy caterpillar by its fuzz or hair density. For example, the Virginia tiger moth caterpillar (Spilosoma virginica) is densely covered with hair, whereas the saddleback caterpillar (Acharia stimulea) is brown and green with tufts of hair on its ends and bottom.
Identify the brown, fuzzy caterpillar by distinctive features. For example, the hag moth caterpillar (Phobetron pithecium) has projecting knobs that make it look like a mini octopus. The pine tussock moth caterpillar (Dasychira pinicola) has sharp-looking spines. The pine devil caterpillar (Citheronia sepulcralis) has horns on its head.
Determine the species of caterpillar using online resources. Search the Discover Life database by selecting filters according to the physical attributes you noted. Visit the Northern Prairie Wildlife Research Center website and select families such as Arctiidae and Lymantriidae to look at pictures of some of the corresponding species. Look at a multitude of pictures on the Bug Guide website.
Register for a free account on the Butterflies and Moths of North America website if you have not been successful at identifying the brown, fuzzy caterpillar. As a member, you can submit a picture of the caterpillar to be identified by a regional naturalist.