Excerpts from Jim Conrad's
from the May 18, 2014 Newsletter issued from the Frio Canyon Nature Education Center in the valley of the Dry Frio River in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau, USA
My Collard plants bolted several weeks ago but I'm letting them flower and fruit, to collect seeds for later plantings. Colorful but smallish caterpillars, reaching only about 3/4-inch (17mm) have appeared chomping on the leaves, as shown above.
These are such distinctive larvae that Bea in Ontario quickly identified them as Cross-striped Cabbageworms, EVERGESTIS RIMOSALIS, a species fairly common in the eastern US, especially the warmer states, and Mexico. The picture shows that younger caterpillars are darker than older ones.
Cross-striped Cabbageworm caterpillars feed on various members of the Mustard Family, including wild ones, but usually are noticed on garden cabbage, collard greens and Brussels sprouts. They pass through four skin-shedding phases, or instars, before pupating and eventually metamorphosing into smallish, triangular-shaped, blotchy-gray moths not nearly as eye-catching as the caterpillars.
Unlike many garden pests, this species is thought to be native American. It's been accidentally introduced into Australia and Jamaica.