Williston-hammertail
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Efferia willistoni
Williston Hammertail
Efferia willistoni is a species of robber fly in the family Asilidae, commonly known as the Williston Hammertail. It is one of approximately 200 species in the genus Efferia, a diverse group of predatory flies distributed primarily in the Americas. The species was described by Hine in 1919. As with other asilids, it is presumed to be an active aerial predator of other insects.