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Caterpillars of Pacific Northwest
Forests and Woodlands

Common Families


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. (30 species) 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. (1 species) Phryganidia californica, which occurs on oak and chinquapin. External leaf feeders. The adults are night-flying moths.

Drepanidae - the caterpillars of hook-tip moths. (2 species) Drepana arcuata which is common, and D. bilineata, which is not common. External leaf feeders occurring primarily on broadleaf plants, in particular on alder species. Two features are characteristic: the rearward projecting knob on Al0, and the prolegs on A10 which project backwards and lack crochets. Full grown caterpillars may be 30 mm in length. The adults are night-flying moths.

Gelechiidae - the caterpillars of gelechiid moths. (200 species, but poorly documented) Habits and habitats varied: external leaf feeders, borers, tunnelers, in flowers, in seeds, and leaf tiers; occurring on conifers and broadleaf plants. The caterpillars are fairly nondescript making field identification difficult. Identification is best achieved using keys which rely on the arrangement of hairs. Most full grown caterpillars are less than 15 mm in length (Telphusa sedulitella). The adult moths are night-flying.

Geometridae - the inchworms or loopers. (400 species) This family is second to the noctuids in containing the most species of Lepidoptera in the Pacific Northwest. Either one pair of midabdominal prolegs which occur on segment A6 (Group A-1), or two pairs, which occur on segments A5 and A6 (Campaea perlata). Most species feed either on conifers or broadleaf plants, few on herbs and grasses. Full grown caterpillars in small species may be only 20 mm while large species may be 70-80 mm long. For most of the species the adult moths are night-flying.

Hesperiidae - the caterpillars of skippers. (40 species) External leaf feeders but may be found within tied leaves, occurring primarily on broadleaf plants, including many species associated with grasses. The most diagnostic trait for identification is that the first segment of the thorax is constricted. See Epargyreus clarus. A full grown caterpillar may be 50 mm in length. The adults are day-flying butterflies.

Lasiocampidae - the tent caterpillars and caterpillars of lappet moths. (6 species) External leaf feeders, occurring primarily on broadleaf plants. Medium to long hairs, which may be densely packed on the body. The hairs are often more densely arranged sublaterally as in Phyllodesma americana. Among the common hairy caterpillars of the Pacific Northwest, the biordinal crochets of lasiocampids are unique. A full grown caterpillar may be 100 mm in length. The adults are night-flying moths.

Lycaenidae - the caterpillars of hairstreaks, elfins, blues and coppers. (60 species) External leaf feeders, occurring primarily on broadleaf plants. Covered with many short hairs, giving the appearance of velvet. The head is usually concealed from above by the prothorax. The dorsal aspect of the body is humped, a feature best seen in lateral view (Group B-2b - Humped in profile, head concealed). A full grown caterpillar may be 30 mm in length. The adults are day-flying butterflies.

Lymantriidae - the tussock caterpillars. (8 species) External leaf feeders, occurring on conifers and broadleaf plants. Typically, tufts of dense hair occur middorsally on segments A1-A4; a brightly colored (red or orange) exposed gland middorsally on segments A6 and A7, as in (Orgyia antiqua). An introduced species, Leucoma salicis, does not fit the description of a typical lymantriid caterpillar in the Pacific Northwest. A full grown caterpillar may be 60-70 mm in length. The adults are night-flying moths.

Noctuidae - the caterpillars of cutworms, armyworms, semi-loopers, and underwings. (850 species) This family contains the highest number of species among all families of Lepidoptera in the Pacific Northwest. Habits and habitats varied, some species occur in the soil, others bore in stems, and many are external leaf feeders. Host plants include conifers, broadleaf trees and shrubs, herbs, and grasses. Caterpillars may be hairy as in some species of Acronicta, nearly naked as in the species of Lithophane, brightly colored as in Zotheca tranquilla, or cryptic as in the species of Catocala. The Plusiinae are recognized by the presence of only two pairs of midabdominal prolegs (on A5 and A6). All other noctuids have four pairs of midabdominal prolegs. Full grown caterpillars of the smaller species may be 15-20 mm, while larger species may be 70 mm in length. The adults are moths and nearly all species are night-flying.

Notodontidae - the caterpillars of prominents. (20 species) External leaf feeders, occurring primarily on broadleaf plants. Prolegs of A10 may be extremely short or extremely long relative to the midabdominal prolegs and are often elevated above the plant surface as in (Furcula cinerea). Caterpillars may be 60 mm when full grown. The adults are night-flying moths.

Nymphalidae - the caterpillars of brush-footed butterflies; fritillaries, commas, admirals, crescents, checkerspots, and tortoiseshells. (50 species) External leaf feeders, occurring primarily on broadleaf plants. Many species have spines middorsally on A7 but not middorsally on A9. The head of nymphalid caterpillars may possess spines as in the species of Nymphalis . These spines are not of the stinging type as in some saturniids. A full grown caterpillar may be 75 mm in length. The adults are day-flying butterflies.

Papilionidae - the caterpillars of swallowtails and parnassians. (10 species) External leaf feeders. Body color in swallowtails is a mixture of green, yellow, and black. Many of the swallowtail caterpillars feed on species of Apiaceae (umbelliferous plants). The parnassians are black with yellow spots and feed on Dicentra or Sedum. Caterpillars of Papilionidae possess an osmeterium, which is an eversible forked pouch, on the prothorax. A full grown caterpillar may be 70 mm in length. The adults are day-flying butterflies.

Pieridae - the caterpillars of whites and sulphurs. (20 species) External leaf feeders, occurring primarily on broadleaf plants. Covered with many very short hairs, giving the appearance of velvet. A full grown caterpillar may be 50 mm in length. The adults are day-flying butterflies.

Plutellidae - the caterpillars of plutellids or diamondback moths. (25 species, but poorly documented) Usually external leaf feeders that may loosely tie leaves together, occurring primarily on broadleaf plants. Body color is often a shade of yellow to green. Generally small, rarely exceeding a full grown length of 15 mm. See Ypsolopha cervella. The adults are night-flying moths.

Pyralidae - the caterpillars of snout moths. (200 species, but poorly documented) Typically borers in plant stems and fruits, occurring on conifers, broadleaf plants, and in nests of other insects. Identification is best achieved using keys that rely on the arrangement of hairs. Usually less than 30 mm in length when full grown. The adults are night-flying moths.

Saturniidae - the caterpillars of silk moths. (12 species) External leaf feeders, occurring primarily on conifers and broadleaf plants. Many species possess scoli which will be present middorsally on A8 and A9 but not A7. The spines of some species are capable of inflicting a painful sting as in Hemileuca eglanterina. The head of silkworm caterpillars lacks spines, whereas the head of nymphalid caterpillars may have spines. A full grown caterpillar may exceed 100 mm in length. The adults are moths and most species are night-flying.

Satyridae - the caterpillars of satyrs. (12 species) External leaf feeders, occurring on grasses. Covered with many very short hairs, giving the appearance of velvet as in Cercyonis pegala. A full grown caterpillar may be 40 mm in length. The adults are day-flying butterflies.

Sphingidae - the hornworms. (25 species) External leaf feeders, occurring primarily on broadleaf plants. A single middorsal horn usually occurs on A8. Caterpillars often rest in a prayer-like pose, with the head and true legs raised above the plant surface. A full grown caterpillar may exceed 100 mm in length. The adults are moths and nearly all species are night-flying.

Thyatiridae - the caterpillars of thyatirids. (10 species) External leaf feeders but are found in loosely tied leaves, occurring primarily on broadleaf plants. The tail end (prolegs are reduced) is often raised above the plant surface. Caterpillars may be 40 mm in length when full grown. The adults are night-flying moths.

Tortricidae - the leaf-tier caterpillars. (300 species, but poorly documented) Typically external leaf feeders but often in a rolled leaf. Many species are leaf miners as early instars, occurring on conifers and broadleaf plants. Identification is best achieved using keys that rely on the arrangement of hairs; however, some species are distinctively marked allowing field identification. A full grown caterpillar of a large tortricid may reach 20-25 mm as in Choristoneura rosaceana. The caterpillars move quickly in reverse when disturbed. The adults are night-flying moths.


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