The Gulf Fritillary (Agraulis vanillae) is a striking, bright orange butterfly of the family Nymphalidae. It was formerly classified in a separate family, the Heliconiidae or longwing butterflies. Like other longwings it does have long, rather narrow wings in comparison with other butterflies. It is not closely related to the true fritillaries. It is a medium to large butterfly, with a wingspan of from 6 to 9.5 cm. Its underwings are buff, with large silvery spots. It takes its name from the fact that migrating flights of the butterflies are sometimes seen over the Gulf of Mexico.
The Gulf Fritillary is commonly seen in parks and gardens as well as in open country. Its range extends from Argentina through Central America and Mexico, the West Indies to the southern United States, as far north as the San Francisco Bay Area on the west coast. It is occasionally found further north in the US.
The larva or caterpillar of the gulf fritillary grows to approximately 4 cm in length and is bright orange in color and covered in rows of black spines on its head and back. The spines are soft to the touch and do not sting. However, the larvae are poisonous if eaten, as the bright coloration advertises. The larva feed exclusively on various species of passionflower such as maypop and running pop.
Their toxic flesh provides gulf fritillary caterpillars with excellent protection from predators. Birds avoid them. Some specialized insects have been observed feeding on them, however, and larger caterpillars sometimes eat smaller ones.
The chrysalis is approximately 3 cm long; it is mottled brown and looks like a dry leaf.
Cultivation of the passionflower in gardens has enabled the gulf fritillary to extend its range, for example into new areas of southern California.