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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Bugs in Orange and Black, Part 2, beautiful but stinky: Gulf fritillary, Agraulis vanillae


The gorgeous Gulf fritillary butterfly harbors a couple of unpleasant surprises for any would-be predator. 


Flowers of the passion vine are among the most magnificent in the plant world.

To celebrate Halloween last week, we visited two insects decked out in orange and black, the dastardly Colorado potato beetle and its deadly nemesis the two-spotted stink bug. This week Bug of the Week finds itself on the sunny shores of South Carolina where brilliant yellow members of the aster clan carpet the sands just leeward of the dunes. Here in the waning days of autumn a beautiful butterfly dressed in orange and black sips nectar in preparation for its journey to frost-free zones along the Gulf of Mexico. The Gulf fritillary is a broad ranging species taking up permanent residence from Argentina to the southern United States. During summer, peregrinations take it as far north as San Francisco on the west coast and New Jersey on the east coast, but in autumn this vagabond travels south to the warm climes of the Floridian peninsula to spend the winter.


Asters provide a rich source of carbohydrates to fuel the Gulf fritillary’s autumn migration to frost-free zones in the Deep South along the Gulf of Mexico. 

Striking contrasts of orange body and black spines may serve as a warning to predators to avoid making a meal of Gulf fritillary caterpillars. 

Like other members of the longwing butterflies, larvae of this orange and black beauty consume leaves of passion fruit vine. The blossom of the passion fruit vine is one of the most gorgeous in the angiosperm world. Exotic flavors of the passion fruit are used around the world to add zest to ice cream, cheesecake, and mixed drinks. Passion fruit is rich in vitamin C and lycopene and consuming this delicacy soothes a queasy stomach according to Andean lore. As a group, passion fruit plants are protected from most leaf-munching caterpillars and other vegan insects by a veritable witch’s brew of highly toxic chemicals including alkaloids, a family of toxins that includes strychnine and nicotine, and cyanogenic glycosides, chemicals that release cyanide upon entering the digestive tract of a caterpillar or human. However, the Gulf fritillary and other members of its clan, including the zebra longwing butterfly we met in a previous episode, turned the tables on passion fruit plants, bypassing the noxious defenses, and feasting with impunity on their leaves. Some species of longwings sequester cyanogenic glycosides from their food and others manufacture these compounds on their own, presumably for defense. The striking orange and black coloration of the Gulf fritillary warns vertebrate predators not to mess with this beauty.


Like its cousin the Gulf fritillary, a zebra longwing caterpillar consumes large quantities of passion vine leaves each day.

In addition to any plant derived defenses, the gorgeous Gulf fritillary has one more bit of chemical trickery to help keep predators at bay. Glands on the abdomen produce and release a concoction of complex esters when the adult butterfly is disturbed. This stinky defensive fluid dissuades predators such as birds from making a meal of these dazzling butterflies. Beautiful but stinky is a recipe for success for the Gulf fritillary.


References used in the preparation of this Bug of the Week include “Caterpillars of Eastern North America” by David L. Wagner; “Coevolution of Animals and Plants” by Lawrence Gilbert and Peter Raven; “Gulf Fritillary Butterfly, Agraulis vanillae (Linnaeus) (Insecta: Lepidoptera: Nymphalidae)” by Jaret C. Daniels; and “Novel chemistry of abdominal defensive glands of nymphalid butterfly Agraulis vanilla by Gary N. Ross,  Henry M. Fales, Helen A. Lloyd, Tappey Jones, Edward A. Sokoloski, Kimberly Marshall-Batty, and Murray S. Blum. We thank the amazing arborists of Trees South Carolina for providing the inspiration for this Bug of the Week.