The Gulf Fritillary or Passion Butterfly, Agraulis vanillae, is a striking, bright orange butterfly of the family Nymphalidae, subfamily Heliconiinae. These were formerly classified in a separate family, the Heliconiidae or longwing butterflies, and like other longwings this species 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 6–9.5 cm (2.4–3.7 in). Its underwings are buff, with large silvery spots. It takes its name from migrating flights of the butterflies 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, Mexico, and the Caribbean to the southern United States, as far north as the San Francisco Bay Area on the west coast. It is occasionally found farther north in the US.
The larva or caterpillar of the Gulf Fritillary grows to approximately 4 cm (1.6 in) 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 larvae feed exclusively on species of passion flower such as Maypop (Passiflora incarnata), Yellow Passionflower (P. lutea) and Running Pop (P. foetida).
Their toxic flesh provides Gulf Fritillary caterpillars with excellent protection from predators. Many birds avoid them. Some specialized insects are observed feeding on them, however, and larger caterpillars sometimes eat smaller ones. This species belongs to the "orange" Batesian mimicry complex.
The chrysalis is approximately 3 cm (1.2 in) long; it is mottled brown and looks like a dry leaf.
Cultivation of passion flowers in gardens has enabled the Gulf Fritillary to extend its range, for example into new areas of southern and northern California.