Robber flies are known to eat a wide range of prey. They have been known to capture other flies, beetles, butterflies, moths, various bees, ants, dragonflies, damselflies, wasps, grasshoppers, and some spiders. This widely varying diet is not opposed to the typical olfactory-based defense mechanisms that some insects implement—a.k.a. they’ll eat “smelly” bugs. They have been known to deliver painful bites to humans if they are handled without care. To capture their prey, they will stab it with its short, strong proboscis, and inject a neurotoxic and proteolytic saliva which paralyzes and begins to digest the victim. They will then suck the liquefied insides of their victim through the proboscis.

The lifecycle of a maroon-legged lion fly takes between one to three years. After hatching from the egg, this robber fly will progress through found larval stages and one pupa stage before becoming an adult. As in their adult stage, they are also predators during the juvenile stages, feeding mostly on insects. Female robber flies will lay white eggs on low-lying plants and grasses, or in cracks in soil, bark, or wood. These eggs are typically laid in masses.