Fly Buffet

Happy autumn!  I am now exactly three months behind in sorting my photographs.  To celebrate the occasion, I thought I’d share this quaint little scene I just came across from the first day of summer: a whole bunch of different flies slurping on a bird dropping together.  If you’re still with me after that bot fly post, I figure I don’t have to worry about grossing anybody out.

I’m not really sure, but my best guess is that the big one is some kind of muscid, a member of the family that includes the common house fly.

The rest of them are frit flies (Chloropidae), but there seem to be several different kinds in attendance.

Many have fed with such enthusiasm that it looks like their abdomens are about to burst.

One that had evidently had its fill stepped off the bird dropping and started blowing bubbles.  There is a forum topic devoted to this behavior here, and a collection of photos showing flies and a few other insects doing it.  The best explanation seems to be that they blow bubbles after ingesting liquid food to evaporate water and thereby concentrate nutrients.

At one point a lone rust fly (Psilidae: Psila collaris) joined the festivities.

So much to see on one little bird dropping.  You can see why I don’t make it very far when I go for a walk.

Added 5/23/2012: Terry Wheeler has identified all of the frit flies as Gaurax species, based on photos I submitted to BugGuide.net.  There may be as many as four different species present.  The bubble-blowing one is G. pseudostigma, and the one with the all-black thorax is probably G. pallidipes.  Terry adds: “Habits of Gaurax are very poorly documented and many of the species are known only from the original specimens from one or a few sites, so photos such as yours are a gold mine. Gaurax are rare, but when they do occur in numbers there seem to be lots of species mixed up together.”