Q This past summer, we experienced an incredible, disgusting infestation of blowflies (metallic blue-green flies that lay eggs in carrion). We almost moved out of the house for the duration. There were thousands of them. What size animal must there have been, decomposing in my house, to support 1,000 blowflies? A professional sprayed inside and out, but no source was found. He concluded that they must have been hatching out of a carcass somewhere in the walls or chimney and would die off as the food source for the larvae was used up. The old hanging sticky-ribbon traps were effective, but they were revolting and unsanitary. How can we keep this from happening again?

A It's difficult to accurately guess the size of the animal that was the source of your blowflies. It's safe to say, however, that it was a moderate-sized animal, such as a squirrel or raccoon. Although it's challenging to tolerate such a large number of flies, they did you a service by consuming the carcass.

To prevent a repeat of this problem, pest-proof the outside of your home. If you can keep animals out, they won't have an opportunity to get inside, become trapped and die.

Walk the perimeter of your home and look for access points for animals. Screen or otherwise seal openings to prevent animals from gaining entrance. Don't overlook the dryer vent, kitchen and bath vents, air intake and exhaust vents for furnaces, the chimney and the attic or roof. You may want to consider hiring a professional who is experienced with wildlife control for this job.

Jeff Hahn, entomology department, University of Minnesota Extension

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