You are about to feel silly — bags of water do deter flies

Clay Thompson

Today’s question: Our downstairs neighbor hangs clear plastic bags filled with water from the ceiling of her patio. One of the bags is marked “shoo-fly bag.” She seems to actually believe that these repel flies. Do bags like this really have any effect on flies? My boyfriend and I think she’s an idiot. Do you agree?

Idiot? That’s a bit harsh, don’t you think? Why don’t we say misguided instead?

So, let’s see if you can take it as well as you give, because in this case the misguided shoe is on your foot.

Putting up those plastic bags to repel flies is a fairly common practice in these parts. If memory serves I’ve written about it a couple of times over the years, and I’ve even tried it myself, although I am not particularly infested by flies. And I know others who have done so. Some stables and some restaurants with outdoor dining use the plastic-bag trick.

What you do is get some sandwich or freezer bags with that sliding-lock thingy. Fill it about half full with water and hang it with some clear fishing line or something like that.

It works, but nobody seems to know why for sure.

One idea is that it might look to a fly like a hornets’ nest.

The idea I come across most often is that the bag of water distorts the vision of a fly’s many eyes so the pest moves on.

So, I guess you’re just a little bit embarrassed now about making fun of your neighbor, aren’t you? I should hope so. You should bake some cookies and take them downstairs to her. It will help you get away from the flies.