[thedoc (OP)]

BCG asked the Naked Scientists:
   
I have a 'mutant' fly in my window! I'm outside Cincinnati. We just had the coldest winter in 20 years. I closed my bedroom window (for winter) in early November 2013. I noticed that a housefly was trapped between the screen and the glass. We have had a few spells of warmer weather during the winter, but I never open the windows. I have periodically seen this fly, still trapped between the screen and glass all through the winter. As I sit her today 3/7/2014..the window is still closed since November 2013 and this crazy fly is awake and flying around trapped between the screen and the glass. Being just a screen, that fly has been exposed to wind chills of 30 below 0. And yet, he lives! How is this possible?
What do you think?

[CliffordK]

Most interesting, assuming it is the same fly. 

According to the notes I'm seeing, the lifespan of the common housefly is about 30 days.  You're suggesting that your fly is about 4 to 5 months old.  Perhaps they go into hibernation as the temperatures drop to below 40 or 50 degrees or so.  I would imagine they could resist spring and fall frosts. 

How cold do you keep your house?  Do you get ice crystals forming on the windows?  Inside or outside?  Single or double paned windows?  It is quite possible that the screen blocks the wind and slows heat exchange between the window and the rest of the environment, and thus the fly might have been heated by the house somewhat and also protected from the bitter outside temperatures. 

If, however, it is hibernating, it may not be able to tell the difference between a 30 degree morning frost and a sub-zero winter month.