Robber flies are voracious predators of other insects. The robber flies have a distinctive cleavage between the eyes on the top of the head and many have hairs on the front of the head called a mystax. The robber flies wait on foliage for prey to fly by. The robber flies are swift and agile flyers that attack their prey in the air. The legs have sharp spines and the ends of the legs have sticky pads called pulvillae that secure the prey. The robber fly has sharp sclerotized mouthparts that form a syringe-like tube that can pierce the prey. The robber fly injects digestive fluids that quickly subdue and paralyze the prey.
Flying insects attacked by robber flies often struggle and thrash about.The mystax prevents the thrashing prey from contacting the head of the robber fly and prevents the prey from doing major damage. Robber flies will return to the perch to finish their meal. Robber flies are common in Indiana and often will land on hikers. Robber flies typically do not bite people. However they should be handled carefully because they will bite if they are threatened.