Phorid Flies

Phorid fly from our sink

This may be the smallest fly in your house that you have never seen. Occasionally I will see tiny dark insects, 4mm long, darting around in jerky movements in the kitchen sink by the compost container. They were impossible to photograph while darting around, never flying away.  I finally caught one in a small container and tossed it in the freezer - yes, my Master Naturalist live-in editor is extremely tolerant.

Under magnification I was surprised to see one pair of wings typical of the order Diptera, and impressively long legs.  Chris Barnhart identified them for me as flies in the family Phoridae.  They are lovingly referred to as scuttle flies, coffin flies or laboratory flies.  The scuttle refers to their habit of darting around to escape rather than flying away.

As you might guess, many species eat decaying materials including some that can persist in a sealed coffin for long periods of time.  They are commonly found around kitchens, sinks and in laboratories which house research animals.  Many Megaselia species are found feeding on fungi.  The "world's smallest fly", Euryplatea nanaknihali (0.4 mm, the size of a grain of pepper), is a phorid fly. 



The most interesting group is Apocephalus (apo - away from, cephalus - head).  Many of these species are known as ant-decapitating flies.  They will lay their eggs on ants' abdomens.  When their larvae emerge they move up to the head, feeding on it until the ant's head until it falls off, sometimes while the ant continues to move.  On the other hand, members of the genus Dohrniphora actually will bite the ant's head off and haul it off as seen on this video.

While we may not have a lot of sympathy for ants, bees are another matter.  A. borealis lays its eggs on bumblebees and wasps, with the larvae moving into the bee's head.  The parasitized bee has been called a "Zombie Bee" because of its tendency to act crazy and fly at night before dying.  About a week later the flies emerge, decapitating the bee.  Last year attacks on honey bees were confirmed, also documenting the fly can transmit deformed wing virus and Nosema ceranae, suspected factors in Colony Collapse Disorder.

When compared to others of the order Phoridae, our occasional visitors are rather benign.  I guess I will have to learn to put up with them, especially since I am too slow to squish them.