I strongly, strongly dislike houseflies.
Most insects (and spiders) I’m just fine with them staying in their area and me staying in mine.
Houseflies, however… blech.
Controlling these pests is a matter of choosing what bad side effect you’re going to have. Many traps are useless. Some (like bug zappers) may be ineffective or even attract more of them to you. And pesticides are… well, poison, and not just for insects. The trap I’m about to show you does take a bit of plastic out of the recycling stream, but given the alternatives, I think it’s worthwhile.
A video tutorial is below, or you can see the step-by-step pictures below. You’ll notice that my design is a bit different than many soda bottle traps; I’ve found that this design works better with houseflies.
It’s pretty simple. You take a plastic bottle and cut it around where it starts to curve.
Smooth sided bottles (like the other one in this tutorial) are better, but this will work just fine. You take the cap off, invert the top part and fasten it together. I’ve used staples, packing tape, and duct tape before; it all works just fine.
Then you cut two or three slits in the top (soon to be bottom) edge of the bottle. They should be about an inch to an inch and a half tall and two or so inches across.
Then you get yourself some bait. In my case, I took some fresh cat poop that was kindly left on the floor by a certain feline.
I took the bottle and poop outside, found a nice flat spot (a bit of out-of-the-way concrete in my case), placed the poop on the ground, and then inverted the bottle over it.
Within ten minutes there were flies getting trapped inside the bottle, and after two hours there’s a couple of dozen flies (even though it started raining). By a cautious estimate, eliminating these flies could prevent somewhere between 4,500 and 7,000 fly descendants a month down the line.
(Female flies lay between a total of five to six batches of 75 to 100 eggs each. Assuming two dozen flies are trapped in there, half of which are female. Lower bound is 12*5*75, upper bound is 12*6*100. And that’s not counting those flies breeding.)
So don’t wait – controlling fly populations early in the season has a huge effect later on.