Northwest Naturalist

Nematocampa resistaria “Horned Spanworm Moth” Geometridae, male

Clinton, MT
July 25, 2015
Robert Niese

This species of inch-worm moth is found throughout the US, except the southwest, and exhibits striking variation in morphology across its range. Males and females are also quite dimorphic. Males tend to be yellower and have dark patches at the base of their forewings while females almost always have a white ground color. Perhaps the most intriguing aspect of the morphology of this species are the horns of their caterpillars. Look for these crazy caterpillars in mixed hardwood/conifer forests in the early summer here in the PNW.