Oedemasia salicis

Adults are distinguished from similar Oedemasia species by genitalia examination; O. salicis occurs further west than O. leptinoides. Caterpillars are identified by the single red dorsal hump combined with green body coloration and association with Salicaceae hosts. The red hump distinguishes it from green prominent caterpillars (Heterocampa) which lack this feature.

Riparian areas, wetlands, and moist woodlands where willow and poplar grow. Found from low elevations to montane zones.

Western North America from Alaska and western Canada south through the Rocky Mountains to California, Arizona, and New Mexico. Absent from eastern North America.

Adults fly from late spring through summer, primarily June to August depending on elevation and latitude. Single generation per year in most of range; partial second generation possible in southern areas.

Larva feeds on leaves of willow (Salix) and poplar/cottonwood (Populus). Has been observed on multiple Salix species.

• Salix - larval food plantMultiple species
• Populus - larval food plantIncluding cottonwoods

Overwinters as pupa in cocoon. Adults emerge in spring, mate, and females deposit eggs on host plant leaves. Larvae feed through summer, mature, and pupate in late summer or fall. Single primary generation; some southern populations may have partial second generation.

Adults are nocturnal and come to light. Larvae are solitary feeders. When disturbed, caterpillars may arch the body to display the red hump, a possible defensive posture.

Herbivore on riparian willow and poplar. Serves as prey for birds, parasitoid wasps, and other natural enemies. Contributes to nutrient cycling in wetland ecosystems through herbivory and as detritus in pupal stage.

Occasional minor pest in willow plantations or nurseries. Caterpillar's distinctive appearance makes it notable to observers. No significant economic impact documented.

• Oedemasia leptinoidesEastern counterpart with overlapping adult morphology; distinguished by distribution and male genitalia. Caterpillars similar but range allopatric.
• Heterocampa speciesSimilar green caterpillars with tubercles, but lack the distinctive red dorsal hump and have different head capsule shape.
• Schizura speciesRelated notodontids with variable caterpillar coloration; Schizura unicornis caterpillar has a single horn rather than a red hump.

• Notodontidae
• prominent moth
• western North America
• willow feeder
• red-humped caterpillar
• riparian

• BugGuide
• iNaturalist taxon
• Catalogue of Life