You may well have seen a robber fly (also known as an assassin fly) and not recognized it as such. Big eyes, pointed mouthparts, a hairy face and a fondness for insects are robber fly characteristics to look for.
Robber flies are among our largest flies and are predatorial ambushers. They tend to perch for minutes at a time on the tips of leaves, or other sunny viewpoints, where they keep a lookout for unsuspecting prey. Once they spot an insect they lose no time in darting after it. With their beak-like mouthparts they spear the insect and inject a mixture of nerve poisons and enzymes that liquefy the tissues of their victim. They then drink the innards of their prey.
Note that there is a prominent “beard” or tuft of bristles (mystax) in the front of the pictured robber fly’s face. All robber flies have this tuft which serves to protect the face and eyes of the predator from the struggling prey as it dines.
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