Great Southern White
Ascia monuste
Description 1 3/4-2 1/4" (44-57 mm). Large. Male white with pointed, full wings. Charcoal scales dust tips and surrounding veins of FW above; below, FW tips and entire HW creamy, unmarked yellowish. Female dimorphic, either like male but with darker margins, or entirely suffused with smoky brown or gray scales; dark form mostly migratory phase.
Similar Species Florida White lacks dark tips and has narrower more pointed wings. Giant White has black cell spot on FW.
Life Cycle Caterpillar pale or bright yellow, striped greenish-maroon; feeds on wide array of cultivated and wild crucifers, capers, and saltworts, including pepper grass (Lepidium virginicum), saltwort (Batis maritima), and spider flower (Cleome spinosa).
Flight Year-round in southernmost part of range, warm months farther north.
Habitat Beaches, salt marshes, coastal plains, offshore islands, and sandy flats.
Range Neotropics: S. Texas, Gulf Coast, and Florida, emigrating up Mississippi Valley to Kansas and up Atlantic to Virginia.
Discussion Because the striking dimorphism of the female depends upon length of day, a higher proportion of the summer population is of darker color. Generally common, the Great Southern White builds up to enormous numbers prior to northerly emigrations, which occur irregularly and are probably due to a local scarcity of food. The mass movements are very impressive - for days, the large butterflies pass in small clusters, flying in a rapid and very directed manner 15-20' (5-6 m) in the air.
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