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Field Guide Descriptions: Covell (1984) | Online Photographs: MPG, BugGuide, iNaturalist, Google, BAMONA, GBIF, BOLD | Technical Description, Adults: Forbes (1923) | Technical Description, Immature Stages: Dyars (1899); Wagner (2005) | |
| Adult Markings: In this species the thorax and head tend to be rusty brown and the antennae and palps brown. The ground color of the forewing varies from grayish brown to yellowish brown and has scattered, dark brown flecking throughout. The forewing has two dark, straight lines that are pale-edged posteriorly. One line runs diagonally from about the midpoint of the inner margin to the subapical region of the costa at about four-fifths. The other runs parallel to the outer margin from near the anal angle to the costa just below the apex. The two lines converge towards the costa, but do not join and are separated by a small gap. This species does not rest with the abdomen curled upward between the wings as seen in some slug moths. |
| Wingspan: 25 mm (Forbes, 1923) |
| Adult Structural Features: The male's antenna is pectinate and the palps do not reach the vertex. There are two pairs of spurs on the hind tibia in both sexes (Forbes, 1923). |
| Adult ID Requirements: Identifiable from good quality photos of unworn specimens. |
Immatures and Development: Dyars (1899) studied populations near the northern range limit in New York where the adults emerge in the early evening and mate. The females lay whitish eggs the following night either singly or in small groups on the undersides of leaves. The larvae rest on the undersides of leaves and have eight instars before pupating in late summer. The fully grown larvae vary from 13.5-18.5 mm and pupate on the ground where they spin a dark brown to blackish cocoon. The cocoon is relatively thin and less firm than those of other slug moths. The larvae overwinter in the prepupal stage and pupate in the spring.
The slug-like larvae are stocky with a pale green body. The later instars have a dorsolateral row of stinging spines on each side. The dorsal spines are borne from red-orange warts that are connected by a thin, yellow stripe (Wagner, 2005). The lower margins of the body and thoracic region have smaller clusters of spines that are born from faint red-orange warts, while the posterior end has two prominent tails or horns that are armed with black and white spines. Most specimens are marked with a series of wavy, vertical, pale yellow lines along the sides, along with two parallel, undulating, pale-yellow lines in the mid-dorsal region that resemble a series of hourglass-like marks. |
| Larvae ID Requirements: Identifiable from good quality photos, especially where associated with known host plants. |