Why do I have Cluster Flies at Home?

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Having large masses of buzzing cluster flies in your windows can be unnerving, and for some people, it seems to be a regular pattern. If you are finding you have swarms of houseflies gathering in your windows, it’s time to figure out why and what to do about it. Talking to a professional or getting a pest control system (click this link for more on that) can help if necessary.

What are Cluster Flies?

Before we talk about dealing with them, you should be clear on what these are. Technically, cluster flies are a specific species of fly (Pollenia rudis) that tends to gather in large numbers, but most people use the term whenever they have a swarm of any kind of housefly. Regardless of the actual fly species, “cluster flies” are the kind of unpleasant problem that many homeowners have to deal with at one time or another.

Why do You Have Them?

Flies are drawn to heat and light, which is what makes a warm window such a strong magnet for them. In particular, those spring days when the air is still cold, but the bright sun heats up the glass are the worst for attracting flies. Certain fall days can create the same environment, though it really can happen anytime.

Of course, the warm windows don’t actually create your flies. They are already in the house unless you are dealing with a poorly sealed window. The windows just bring them all together.

Dealing with Them

Keeping the curtains or blinds closed can help keep them out, though that doesn’t really get rid of the flies. Just blocks them from the glass. In some ways, cluster flies are actually easier to take care of than individual flies because of the way they are all concentrated in one spot. Take advantage of that.

A sticky film window trap can be very effective. Stick one or two to the glass, and the flies will soon trap themselves as the crowd around the window. Remember to replace them as they fill up though. You can also kill a number of flies in one go with a can of bug killer spray, though you’ll probably have to return and check the window a number of times to deal with ongoing new flies. A sticky trap works whether you are there or not.

And you should also pay some attention to prevention so that new clusters don’t start building up. Have secure screens on all your windows, and keep all garbage in tightly covered containers (or out of the house entirely) to keep the overall fly population down. If you still seem to have an ongoing problem with flies in the house, you may need to investigate further. There maybe cracks in the seals around windows, torn screens or gaps in the siding that are letting flies into the house.

If left unchecked, cluster flies are almost certain to lead to a big increase in your indoor fly population because flies in small spaces are more likely to quickly breed and start laying eggs. You don’t want that.