Salt Marsh Caterpillar

Estigmene acrea — the salt marsh caterpillar — is one of the most familiar 'wooly bear' caterpillars in North America and one of about 11,000 species in family Erebidae (which includes the tiger moths and many other moths). The species is widespread across all of North America from southern Canada south through the eastern and central US to South America. Larvae are 4-5 cm long when fully grown, heavily-furred wooly bear caterpillars with the species' diagnostic feature: EXTREME COLOR POLYMORPHISM. Salt marsh caterpillars range across a continuous spectrum from LIGHT YELLOW-ORANGE individuals through orange-tan, reddish-brown, dark brown, and nearly black variants — sometimes all colors are represented within a single brood from one egg mass. The color variation is one of the most-cited examples of CONTINUOUS COLOR POLYMORPHISM in NA Lepidoptera and is genetically heritable but also influenced by environmental conditions (temperature, host plant, larval density). The species is famous in the southeastern US for AUTUMN OUTBREAK MIGRATIONS — when fully-grown salt marsh caterpillars descend en masse from host plants and crawl across roads, sidewalks, and gardens in search of pupation sites in soil and leaf litter. The autumn migrations are particularly conspicuous in Texas, Louisiana, Florida, and other southeastern US regions, where outbreak years can see dozens-to-hundreds of caterpillars crossing every meter of road over several days. The migrations are a major nuisance for drivers (roads can become slippery from crushed caterpillars), but the migrations don't cause significant agricultural damage (the caterpillars are leaving feeding sites, not entering them). Larvae feed on a wide range of plants — over 80 documented host plant species, including grasses, forbs, vegetables (cabbage, lettuce, beans), and various other crops. The 'salt marsh' part of the common name comes from the species' frequent occurrence in salt marshes and coastal wetland habitats, where larvae feed on salt-tolerant grasses. Adult moths are striking 4-5 cm wingspan TIGER MOTHS with white forewings marked by bold black spots and yellow-orange abdomens with dark spots — the warning coloration is APOSEMATIC (warning coloration) signaling chemical defense from sequestered host plant compounds. Adults are nocturnal, fly at night, and are commonly attracted to porch lights. The species is harmless to humans (no urticating hairs in the larva — the heavy fur is purely visual) and is one of the most-photographed wooly bear caterpillars in North American backyard nature photography.