Large caterpillar about 50 cm high on a flowering Euphorbia esula stem on a dry floodplain bench with very scattered Euphorbia esula among Agropyron intermedium, Bromus inermis, and 2/3 m tall Prunus virginiana sprouts regrowing from fire last fall. Full sun, 95 F, early afternoon, light breeze.

Elevation ca 4000 feet. Disturbed, shrubby riparian corridor on stream restoration site within a patchwork of native and non-native grassland.

This has apparently been a good year for this species here. On 5 July I counted 15+ more larvae across several small riparian Euphorbia esula patches about 1 km downstream along Sevenmile Creek.