The larval stages of moths and butterflies (Lepidoptera) are called caterpillars. Larvae of the sawflies, a group of wasps, are also called caterpillars, but none are known to be pests of field crops in North Carolina. Larvae of other insects are called maggots, grubs, worms, or just larvae. Lepidopterous larvae may be separated from other kinds of larvae in the following key. There is no convenient way to key out the relatively few species of pest caterpillars from the much larger number of nonpest species except by the presence or absence of significant damage to the crops on which they occur.

This key will separate the more common pests in North Carolina. If a caterpillar is not numerous or does not cause significant damage, it is not likely to be in this key. If, after examining several specimens, caterpillars will not key out, you may want to send them to a taxonomist for identification. In many cases, caterpillars feeding only on weeds in or around the field need not be identified. However, any large population of defoliating caterpillars or stalk borers should be observed regularly until their development is complete. If they do become a problem, they need to be identified so that a control tactic can be selected.

Certain terms and diagnostic features of caterpillar anatomy must be learned to use this key. These terms and features are labeled on illustrations accompanying the key or defined in the glossary at the end of this text. It is often impossible to identify caterpillars on the basis of color alone because of variability within species and similarity between them. The most reliable characteristics may be too difficult to see with a hand lens or on a live, squirming specimen. Therefore, this key relies upon body features, behavior, hosts and injury symptoms as well as color and pattern. To use this key most effectively, you need a 10x hand lens and a pocket knife.

Key to Caterpillars

1. Larva with three pairs of thoracic legs, each leg bearing a short sharp claw; one to four pairs of abdominal prolegs and one pair of anal prolegs, each proleg bearing many crochets (except saddleback caterpillar, see couplet 2)(Fig. 1A,B,C) . . . . 2
   

   Larva with or without thoracic legs, abdominal prolegs usually absent; if abdominal prolegs present (sawflies), then there are five to seven pairs and they lack crochets (Fig. 2) . . . . OTHER INSECTS

   

2. Larva lacking prolegs but has a pair of fleshy, spine-covered lobes at each end of body; back green and purple with a central spot (Fig. 3A,B) . . . . SADDLEBACK CATERPILLAR

   Has distinct prolegs; coloration different . . . . 3

   

3. Larva with single, curved horn (Fig. 4,5) sometimes to 89 mm (about 3 1/2 inches) long . . . . 4

   Larva without horn; usually less than 51 mm (about 2 inches) long . . . . 5

   

4. Horn reddish; a single, diagonal, pale line on side of each abdominal segment (Fig. 4) . . . . TOBACCO HORNWORM

   Horn bluish or greenish; two pale lines on side of each abdominal segment, forming a V-shaped mark (Fig. 5) . . . . TOMATO HORNWORM

5. Larva distinctly fuzzy, with long hairs . . . . 6

   Larva apparently hairless, with 12 or fewer fine hairs per side of each body segment . . . . 7

6. Has three pairs of abdominal prolegs; body small, 13 mm (1/2 inch) or less in length; in sorghum heads (Fig. 4) . . . . SORGHUM WEBWORM

   Has four pairs of abdominal prolegs; body larger, to 39 mm (1 1/2 inches) or more (Fig. 7) . . . . SALTMARSH CATERPILLAR

   

7. Has one pair of abdominal prolegs (Fig. 8) . . . . INCHWORMS (SPANWORMS, GEOMETERS)

   Has two or more pairs of abdominal prolegs . . . . 8

   

8. Has two pairs of abdominal prolegs (Fig. 9A,B) . . . . CABBAGE LOOPER and SOYBEAN LOOPER

   Has three or more pairs of abdominal prolegs . . . . 9

   

9. Has three pairs of abdominal prolegs; uniformly green, thrashes violently when disturbed; found on soybeans and other legumes (Fig. 10) . . . . GREEN CLOVERWORM

   Has four pairs of abdominal prolegs . . . . 10

   

10. Hooks (crochets) on each abdominal proleg arranged in a circle (Fig. 11A) . . . . 11

    Hooks of each abdominal proleg arranged in a straight or curved row . . . . 14

    

11. Body color greenish with reddish or brownish striping and cross banding; body 13 mm (1/2 inch) or less in length (Fig. 12); larva usually in silk tube in soil, tube attached to plant . . . . LESSER CORNSTALK BORER

    Not as above . . . . 12

12. Dorsal pinacula of each abdominal segment with centers paler than margins (Fig. 13); mass of frass and silk dangling from entrance hole in stalk . . . . EUROPEAN CORN BORER

    Dorsal pinacula uniformly colored; frass not as above . . . . 13

    

13. Larva in soil on roots; body 19 mm (3/4 inch) long or less; SD1 pinaculum on each abdominal segment large, partly surrounding spiracle (Fig. 14A) . . . . CORN ROOT WEBWORM

    Larva in stalk; body up to 32 mm (1 1/4 inches) long; SD1 pinaculum small (Fig. 14B) . . . . SOUTHERN CORNSTALK BORER

14. Body longitudinally striped black and white; abdominal segments one to four uniformly blackish (except a middorsal line); head orange with black stripe on side; in stalks (Fig. 15) . . . . STALK BORER

    Not as above . . . . 15

    

15. Skin bearing many small, sharp, hairlike spines (Fig. 16A to C) . . . . 16

    Skin either smooth or bearing pebbly or low, conical granules (Fig. 17A,B; Fig. 18A,B) . . . . 17

    

16. Spines relatively longer and extending onto pinacula D1 and D2 on abdominal segment 8 (Fig 16B) . . . . TOBACCO BUDWORM

    Spines shorter, surrounding but not occurring on pinacula D1 and D2 of abdominal segment 8 (Fig. 16C) . . . . CORN EARWORM, TOMATO FRUITWORM, COTTON BOLLWORM

17. Skin bearing pebbly or conical irregular granules (Fig. 17A, 18A) . . . . 18

    Skin smooth . . . . 19

18. Many skin granules elevated as blunt cones that are as high as wide (Fig. 17A,B) . . . . GRANULATE CUTWORM

    All granules low, like rounded pebbles (Fig. 18A,B) . . . . BLACK CUTWORM

19. Head and body hairs (setae) long, dark and conspicuous, with setae D1 and D2 of each abdominal segment longer than the distance between their bases (Fig. 19A); head without dark markings (Fig. 19B); thrashes violently when disturbed; rarely seen before mid-August . . . . VELVETBEAN CATERPILLAR
    

    Setae shorter, less conspicuous, setae D1 and D2 shorter than the distance between their bases; head usually with dark markings . . . . 20

20. A distinct dark spot present on side of either mesothorax or abdominal segment 1 (Figs. 20, 21A) . . . . 21

    Spot in these positions obscure or absent . . . . 23

    

21. Dark spot present on side of abdominal segment 1 (and sometimes following segments) (Fig. 21A); usually bearing a pair of dark, triangular spots on back of each thoracic and abdominal segment; no white spot behind spiracle on each abdominal segment; body larger, up to 39 mm (1 1/2 inches) long . . . . 22

    Dark spot present on side of mesothorax only [may be difficult to see on larvae less than 13 mm (1/2 inch) long], triangular spots on back much reduced or absent; small white spot present just behind spiracle on each abdominal setment; smaller, up to 25 mm (1 inch) long (Fig. 20) . . . . BEET ARMYWORM

22. Front of head black with a distinct, white, updside-down, V-shaped mark in middle (Fig. 21B) . . . . YELLOWSTRIPED ARMYWORM

    Head uniformly orange, the pale, V-shaped mark present but not distinct (Fig. 22) . . . . SOUTHERN ARMYWORM

    

23. Pinacula D1 and D2 distinct, forming two pairs of dark spots on each abdominal segment (Fig. 23A); head slightly flattened in front; body of uniform diameter throughout; usually occurs midsummer to fall, attacking many crops (Fig. 23B) . . . . FALL ARMYWORM

    Pinacula D1 and D2 absent (Fig. 24A); head more rounded, appearing slightly swollen; body widest at middle, tapering toward each end; usually occurs spring to early summer, attacking grasses and grains (Fig. 24B) . . . . ARMYWORM