Great Southern White

The Great Southern White is a striking, mostly white butterfly in the family Pieridae, particularly associated with coastal habitats in the southeastern United States, the Caribbean, and along the Gulf and Atlantic coasts into South America. It is well known for its occasional mass migratory movements, in which large numbers of individuals travel along coastlines in a single direction, a phenomenon that has fascinated naturalists for generations.

As a member of the genus Ascia, it displays sexual dimorphism and seasonal color forms, with some individuals showing gray-washed wings, particularly in the migratory or dry-season form. It is closely tied to coastal and disturbed habitats where its mustard-family and caper-family host plants establish.

The species is a familiar sight on beaches, dunes, and coastal scrub, where its bright white wings stand out clearly against sand and green vegetation.

• Medium-large white butterfly with a bold black-and-white checkered pattern at the forewing tip and along the outer margin.
• Some individuals, especially migratory-form females, show a gray-brown wash over portions of the wings rather than pure white.
• Body is white to pale gray, and the antennae club is distinctively tipped in turquoise-blue.
• Underside is mostly white to pale yellow-green, with subtler markings than the upperside.
• Distinguished from the Checkered White by its typically larger size, coastal habitat association, and more solid black wingtip patterning.

Great Southern Whites are found along coastal areas of the southeastern United States, the Gulf Coast, Caribbean, and into Central and South America, favoring beaches, dunes, coastal scrub, and adjacent open or disturbed habitats where mustard-family and caper-family host plants grow. Adults are active nearly year-round in the warmest parts of their range, with periodic large-scale migratory flights recorded moving along coastlines, particularly in Florida.

Adults fly with a moderate, somewhat fluttering pattern and are known for occasional mass migratory movements, when large numbers travel steadily along a coastline over days. They visit a variety of flowers for nectar, including composites and coastal wildflowers. Caterpillars feed on plants in the mustard and caper families, including saltwort and related coastal species, and can occur in high densities on host plants during population booms that sometimes precede migratory flights.

Eggs are laid in clusters on the leaves of mustard-family or caper-family host plants. Caterpillars are yellow-green with darker longitudinal stripes and fine hairs, feeding gregariously at first before dispersing, and can build up in large numbers on favored host plants. Pupation occurs in an angular, elongated chrysalis attached to a stem or nearby structure. The species breeds continuously in warm coastal climates with multiple generations per year, and population surges are thought to trigger its notable mass migratory flights.