On March 5, 2003, an audience of WBA members were treated to a presentation by Dr. Merrill Peterson of Western Washington University about the associations between butterfly larvae and ants. This article attempts to summarize the presentation although it cannot adequately convey all the information from Dr. Peterson’s talk and slides.

According to Dr. Peterson, 75 percent of the world’s lycaenid species associate with ants. Some of these associations are obligate (meaning the creatures can survive only when the association exists); some are facultative (meaning the association is beneficial, but not essential). Ants are interested in such associations because butterfly larvae secrete nutritive substances such as amino acids and sugars. In return, the ants serve the larvae as a well-organized militia defending them from predators and parasites.

Butterfly larvae need special adaptations to survive an association with ants-ants tend to be prickly creatures, and they produce formic acid. Some butterfly species are adapted to communicate with ants; others have adapted feeding habits that reduce their vulnerability to ants. Examples of adaptations are the thick cuticle (skin) of many lycaenid larvae. Lycaenid larvae also tend to be slow­ moving which may mean they are less likely to provoke ant attacks. Some scientists believe the butterfly larvae are even able to fool the ants by producing chemical signatures or stridulations that resemble those of ant larvae. Some larvae are adapted to resemble ant larvae so precisely that the ants carry them into the ant nest and rear them as part of their brood. Of course, the ants discover the ruse and danger arises when the larvae in the nest mature into adult butterflies.

The larvae have several organs that contribute to their ant associations. They have a dorsal nectary organ on their seventh abdominal segment that secretes sugars and amino acids that attract ants. Many lycaenids also possess port cupola organs that may produce pheromones that communicate information to ants, sometimes called “appeasement pheromones”.  These pheromones may be similar to scents produced in an ant brood. Some lycaenid larvae may possess stridulatory organs capable of producing grunts, drumming and hissing sounds that resemble sounds produced by ants. Several Washington butterflies take advantage of associations with ants. All of them are believed to be facultative relationships. The species include Edith’s, ruddy and blue coppers; almost all Washington species of blues; hedgerow, gray, and sooty hairstreaks; and moss’ elfin. There may be more undiscovered associations.

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