Short communication: Male-male agonistic behavior and ant-mimicry in a neotropical richardiid (Diptera: Richardiidae)

The Richardiidae are acalyptrate dipterans about which very little is known. Here we describe male-male agonistic interactions and test a hypothesis of ant-mimicry in a new richardiid species in the genus Sepsisoma. Males of Sepsisoma sp. show several ritualized agonistic behaviors, with a clear escalation from simpler to more elaborate displays, which are described here in detail. We could distinguish four (not clearly discrete) behavioral stages during the escalation: Chase, Orientation, Leg display and Body raising. As the displays shifted from simpler to more elaborate, there was also a decrease in their relative frequency. Curiously, small males were by far the most aggressive, and most of their agonisms were directed to large males. The Sepsisoma flies in this study show a clear ant-like appearance, particularly resembling the formicine ant Camponotus crassus. We conducted laboratory experiments which support this hypothesis, providing the first experimental evidence that ant-like dipterans may deceive a potential predator.