In general, caterpillars representing about 21 families of Lepidoptera are commonly collected in the Pacific Northwest. These families are briefly described in alphabetical order. The number of species given in parentheses for each family is only an estimate due to the dynamics of name changes and recognized species status as well as incomplete records for the Pacific Northwest. Arctiidae - the woollybear caterpillars. External leaf feeders occurring on conifers and broadleaf plants.
Many species covered by densely packed, wispy hairs that are longer than the width of the body .
Other species covered by densely packed hairs that are shorter than the width of the body . Nearly all of the species overwinter in the caterpillar stage. A full grown caterpillar may be 60 mm in length. For most of the species the adult moths are night-flying. Dioptidae - the oak worm caterpillars.