Lucilia sp. (Blow Fly).
 
 
 
Size: approx. 5-10 mm. Photo: 07/14/11, 4 pm.


This is the very common Blow Fly or Green Bottle Fly (Lucilia sp.). There are 11 species in North America, which are--at least for me--very difficult to distinguish. 
 
 
bug guide (this photo):
http://bugguide.net/node/view/546611
wikipedia:
http://en.wikipedia.org/wiki/Green_bottle_fly