USGS - science for a changing world

Northern Prairie Wildlife Research Center

  Home About NPWRC Our Science Staff Employment Contacts Common Questions About the Site

Caterpillars of Pacific Northwest
Forests and Woodlands

Key to Families and Species Groups


Less than four pairs of midabdominal prolegs go to group A
Four pairs of midabdominal prolegs go to group B
Group A. Less Than Four Pairs of Midabdominal Prolegs
One pair of midabdominal prolegs, on segments A6 go to group A-1
Two or three pairs of midabdominal prolegs, typically two pairs, one pair each on segments A5 and A6 go to group A-2
Group A-1. One pair of midabdominal prolegs, on segment A6
All of the species of Group A-1 are Geometridae and nearly all of the Geometridae occur in this group.
Body wall with lateral flanges, warts or tubercles group A-1a, see these photos
Body wall smooth group A-1b, see subgroups
Group A-1b subgroups: Body wall smooth
Species of group A-1b are distinguished by color patterns.
Distinct spiracular line, body otherwise more or less uniformly colored or faintly patterned see these photos
Dorsum a different color than subspiracular area see these photos
Distinct subdorsal longitudinal lines see these photos
Middorsal area with a stripe or dots see these photos
Body with distinct patches of color see these photos
Body with no distinct markings, more or less uniformly colored or evenly mottled see these photos
Group A-2. Two or Three Pairs of Midabdominal Prolegs
Typically two pairs of midabdominal prolegs, one pair each on segments A5 and A6. Group A-2 consists of a few species of Geometridae and most of the species of semiloopers that are classified as plusiine noctuids.
Ventral fringe of knobby hairs, prolegs on A5 smaller than those on A6 group A-2a, see this photo
Prolegs on A5 same size as those on A6 group A-2b, see this photo
Group B: Four Pairs of Midabdominal Prolegs
One pair of prolegs on A3, A4, A5, and A6. Except for the Geometridae, all families in group B contain species that fit the description of this group. Species in this group are distinguished by the hairs on the thoracic and abdominal segments.
Without hairs in dense patches, existing hairs not sclerotized, not more than six hairs per segment per side above the spiracular line, hairs shorter than width of abdomen go to group B-1
Hairs in dense patches, not sclerotized, at least seven per segment per side above the spiracular line, hairs of various lengths go to group B-2
Hairs modified into sclerotized spines, scoli, or chalazae go to group B-3
Group B-1. Without Dense Patches of Hairs
Body not covered with dense patches of hairs, existing hairs are not sclerotized and not more than six per segment per side above the spiracular line; hairs are shorter than width of abdomen. Species in group B-1 are arranged by the appearance of the body wall and color patterns. Most of these species are either Gelechiidae, Noctuidae, Notodontidae, Papilionidae, Plutellidae, Sphingidae, or Tortricidae.
Body wall with short tubercles, small warts, asymmetrical swellings, or horns group B-1a, see subgroups
Body wall smooth (except for monarch butterfly) group B-1b, see subgroups
Group B-1a Subgroups: Presence/absence of middorsal horn
Species of group B-1a are distinguished by the presence or absence of a middorsal horn on A8.
Middorsal horn absent on A8 see these photos
Middorsal horn present on A8 (Sphingidae) see these photos
Group B-1b Subgroups: Body wall smooth, except monarch butterfly
Patterns in color on the thorax and abdomen are traits used to distinguish the subgroups.
Pattern of color in rings see these photos
Longitudinal lines straight with at least one even edge see these photos
Longitudinal lines wavy see these photos
Middorsal markings irregular, with patterns of saddles, dashes, or spots see these photos
Body marked with spots, or streaks, or reticulated see these photos
Body without distinct markings, more or less uniformly colored or evenly patterned with faint markings see these photos
Group B-2. With Dense Patches of Hairs
Body with dense patches of hairs, at least seven per segment per side above the spiracular line. Species are grouped by the location of dense hair patches and length of hairs. Numerous families contain species that fit the description of this group, including Arctiidae, Hesperiidae, Lasiocampidae, Lycaenidae, Lymantriidae, some Noctuidae, and Satyridae.
Hairs equal to or longer than half width of body group B-2a, see subgroups
Hairs very short, whisker-like, sometimes barely visible group B-2b, see subgroups
Group B-2a Subgroups: Hairs of different lengths
Species of group B-2a are distinguished by hair length and position of dense hairs.
Tufts of relatively short but very dense hairs occur middorsally on A1-A4 (Lymantriidae) see these photos
Most of the longer hairs occur sublaterally (mostly Lasiocampidae) see these photos
Entire body, or at least half of body length covered in hairs that are longer than body width
(mostly Arctiidae)
see these photos
Less than half of body length covered in hairs that are longer than a full body width
(Acronicta: Noctuidae, Arctiidae)
see these photos
Group B-2b Subgroups: Hairs very short
Species of group B-2b are distinguished by body shape and position of the head.
Body humped in profile, head concealed (Lycaenidae) see these photos
Body not humped, head exposed (Hesperiidae, Satyridae) see these photos
Group B-3. With Sclerotized Spines
Species are arranged by the shape of the spines. Most of these species are either Nymphalidae or Saturniidae.
Hairs modified into sclerotized spines with a single point tip (mostly Nymphalidae) group B-3a, see these photos
At least some of the hairs modified into scoli, with a blunt end and multiple points (mostly Saturniidae) group B-3b, see these photos

Previous Section -- Using the Keys
Return to Contents
Next Section -- Photo Key to Species

Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://www.npwrc.usgs.gov/resource/insects/catnw/keyfam.htm
Page Contact Information: Webmaster
Page Last Modified: Saturday, 02-Feb-2013 05:15:23 EST
Menlo Park, CA [caww55]