Fall 2014 SMTP Interesting Finds: True flies (Order: Diptera)

True flies (Order: Diptera)

Robber flies, also called assassin flies, belong to the family Asilidae. They are powerfully built and have notoriously aggressive predatory habits. They feed mainly or exclusively on other insects and as a rule they wait in ambush and catch their prey in flight.

Robber Fly on Leaf
Robber Fly on Leaf

These predators can be recognized by their usually bearded face and a concave top of the head between the eyes. Robber flies range in length from 1-5 cm, with the females being larger than males.

The fly attacks its prey by stabbing it with its short, strong proboscis (straw-like mouth part) injecting the victim with saliva containing toxic enzymes which rapidly paralyze it and soon digest the insides; the robber fly then sucks the liquefied material through the proboscis.

Stichopogon trifasciatus
Stichopogon trifasciatus

You might hear this species before you see it, as it departs its perch with a loud, buzzing flight, quickly landing again nearby, usually on a vertical branch or twig.


Only one species of robber fly was collected during the program at St. Augustine Catholic Elementary School. Congratulations on this interesting find!

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