<p>All it takes is one fly to lay it’s eggs somewhere and then you are done. It might be someplace warm or in a spot that doesn’t get wiped down, ie, on a windowsill in the crevices of the window frame or under a tv set. Or in a drain. Or near a heater. They could even lay the eggs in a potted plant.</p>
<p>We had a problem a few years ago with it, and I was at my wit’s end. I tried everything. Fly paper, spray, bags, etc. It was disgusting. I kept removing my window screens, letting them out and eventually - knock on wood - all of them disappeared, with no major reoccurence.</p>
<p>Later on I found some casings underneath a portable tv near a sunny window. I think that was the major culprit.</p>