The wingspan is 63–86 mm. Adults are on wing all year round in southern Texas, peninsular Florida and along the Gulf Coast.
Ascia monuste is an example of a migrating species that moves in one direction within its life-span and does not return. It breeds in Florida but sometimes migrates along the coast up to 160 km to breed in more suitable areas.
The larvae feed on Brassicaceae (including Cakile maritima, cultivated cabbage and radish and Lepidium species) and plants in the Capparidaceae family, including nasturtium. Adults feed on nectar from various flowers including saltwort, lantana, and verbena. It is a sporadic pest of crucifer vegetables in southern Texas.