These large flies are approximately 1 1/8 inches (30 mm) in length and have a wingspan of about 2 inches (50 mm). They are completely black except for bright orange on the top of abdominal segment 1. The clubbed antennae are distinctive for this family. Mydas flies resemble wasps in the spider wasp family (Pompilidae). Their body structure also resembles that of robber flies.
The adults can be seen nectaring at flowers, resting on vegetation and actively running around on the ground.
This family includes 50 species in North America with 17 species in the genus Mydas. With their large size and coloration they may be mistaken for wasps, but they are harmless to humans. Eggs are laid singly in soil or rotting wood. The larvae live mostly in decaying wood and are believed to be predatory on beetle grubs, especially June Beetles.
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