The wily musca

My cats seem to have suddenly developed a devotion to ballet, or perhaps contemporary dance.  I see them leaping about the house, bodies extended in ways both improbable and graceful.  What has brought about this aesthetic transformation in my beasts?

Musca domestica.  The common housefly.  

Somehow, over the past week, my house has been populated by an irritatingly large number of these critters, with more outside the windows, begging for entry.  Why now, and why so many?  I don't know.  It isn't as though they are cicadas, emerging at the end of a seventeen-year cycle.

Houseflies are similar to dogs and cats in being associated with human activities -- especially garbage -- for their food.  The relationship is called "commensal," meaning the fly benefits from the relationship, while the human is neither benefited nor harmed (at least directly).  

It's not surprising that flies are everywhere; the mama fly lays eggs in batches of about a hundred.  What's surprising -- to me, at least -- is how they appeared in my house so suddenly.  Flies do hibernate, if the winter is severe enough, and emerge in the spring -- but we've had moderately warm weather for a couple of months.  So, I don't know the answer.

Fly larvae thrive on food waste, carrion, and feces -- none of which can be found lying about in my house, thank you for asking.  Once hatched, they zip through the larval stage in two to five days.

Whatever and wherever their source, they appeared in force about a week ago.  During the day, they seem attracted by daylight and cluster around my windows.  I tried opening the window briefly, and shooing a couple outside.  I'd then encounter flies from the outside who wanted in, even as I was shoving the inside flies out.

Of course, human ingenuity surpasses that of the little musca.  For example, I have at hand an aerosol can of Raid Multi-Insect® killer.  It doesn't kill flies as fast as it kills tiny "pantry moths," but it kills them without fail.  I worry a bit about causing a lingering death, but conclude that a fly's sense of consciousness has not evolved to the point of causing any real agony, physical or mental.  You'll never hear a fly singing the death scene aria from Traviata.  And besides, their life expectancy is only a couple of weeks.  I'm not cutting them down in their prime, just at the point where they've received their admission letter from Harvard.

I intentionally have not killed them all.  The cats have found they can enjoy their role as predator, toying with the struggling fly before ultimately eating it, without subjecting themselves to the dangers and discomfort of the outdoors.  And I enjoy having the cats stick around the house more, rather than ceaselessly prowling about outside, seeking whom they may devour.

So, who says the human host receives no benefit from the commensal fly?