Saltmarsh caterpillar—Estigmene acrea
Saltmarsh caterpillar (family Erebidae) has hairy larvae that vary greatly in coloration and markings. It is an uncommon pest of field and vegetable crops and grapes.
Adults (moths) are about 9/10 inch long with a wingspan of about 1-1/2 to 2 inches. The wings have black spots on top and underneath. On females both the forewings and hind wings are white on top. On males the forewings are white on top and the hind wings are orange on top. The underside of wings of both genders is orange. The abdomen has rows of black spots and is orange on top and underneath and white on the sides.
The eggs are spherical and about 1/50 inch (0.5 mm) in diameter. They are yellow when laid then turn grayish or whitish. Each egg cluster can have up to several hundred eggs.
The larvae (caterpillars) are very hairy with conspicuous tufts of long hairs on each segment arising from colored bumps (tubercles). The body can be dark or pale overall and mostly blackish, brownish, gray, orange, whitish, or yellowish and is commonly a variable mix of colors. See the Moth Photographers Group's photo collage for more of this caterpillar's variable forms. Upon hatching larvae are about 1/12 inch (2 mm) long and at maturity about 2-1/4 inches long.
Pupae occur in organic litter on the ground. They are in a dark brown, thin cocoon about 1-1/4 inches long composed of silk and hairs of the last instar.
Saltmarsh caterpillar develops through four life stages: egg, larva, pupa, and adult. Overwintering is as mature larvae (prepupae) that pupate into adults in early spring. After emerging and mating, adult females lay their eggs mostly on the lower surface of leaves. After hatching the larvae develop through five to seven increasingly larger instars. As they increase in size, they become more hairy.
Egg to mature adult development (1 generation) occurs in about 4 to 6 weeks. There are 3 to 4 generations a year. The caterpillars are relatively uncommon in the spring, but the fall generation is more numerous and causes the most foliage damage.
Young larvae feed in groups that scrape and chew on the underside of leaves; leaf veins and the leaf upper surface remain intact. Older larvae feed individually and chew entirely through leaves, leaving the foliage ragged. Broadleaf weeds such as pigweeds (Amaranthus species) are the most common hosts. The larvae also feed on the leaves of beans, carrots, cole crops, grapes, lettuce, and tomatoes.
The saltmarsh caterpillar has many natural enemies. These include the maggotlike larvae of tachinid flies that feed inside the caterpillars and an Ophion species of parasitoid (parasitic) wasp that is orangish as an adult. As a larva Ophion kills the host during its pupal stage and mummifies the pupal case. This biological control is readily overlooked because the pupae occur in organic debris on the ground and in topsoil.
Saltmarsh caterpillar is a sporadic pest that uncommonly warrants control. If the larvae are intolerably abundant, the underside of infested foliage can be thoroughly sprayed once or more with Bacillus thuringiensis (Bt) or spinosad. Spinosad is toxic to bees and certain beneficial predatory insects for at least several hours after the application so if applying it to plants that are blooming wait until the evening when honey bees are no longer active.
Adapted from Common Name: Saltmarsh Caterpillar Scientific Name: Estigmene acrea (Drury) (Insecta: Lepidoptera: Erebidae: Arctiinae) from the University of Florida and Pests of the Garden and Small Farm: A Grower's Guide to Using Less Pesticide, University of California Statewide Integrated Pest Management Program (UC IPM).