There are 5 North American species in the genus Xanthotype, and they are all virtually indistinguishable from one another. The patterns and colors are all similar and also vary widely within each species. In Missouri, the ones you are most likely to encounter are the crocus geometer (X. sospeta) and false crocus geometer (X. urticaria).
Adults are yellow or tan, with reddish or purplish dots and small blotches.
Larvae are round, light yellow-green or brown, sometimes with reddish lateral lines. They rest with body extended out at an angle and resemble little twigs or shoots. The head is flattened and greenish-white.