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Here’s what to do about the cluster flies at your cottage

One of the benefits of a winterized cottage—aside from warming up by a cozy fire after a winter hike—is the fact that you don’t have to worry about flying insects like mosquitos and deer flies. Unfortunately, cluster flies can be a year-round concern, especially if they’ve managed to enter your home or cottage in the fall through small openings and are now hibernating as unwanted guests in your walls, basements, and attic spaces.

These flies may be relatively harmless compared to biting insects and other pests, but they’re still pesky to have around. Here’s what to do if you’ve spotted a swarm of cluster flies indoors. 

What are they?

There are a number of common clustering flies that you may spot at the cottage, including cluster flies, face flies, and blow flies. Slower and a bit larger than house flies, cluster flies have overlapping wings when they rest, and they’re black and grey with tiny, yellow hairs.

In the spring and summer, these flies lay their eggs outdoors in soil and near earthworm burrows (that’s why cottagers and homeowners with grassy areas may spot more of these pests nearby). The larvae then find and parasitize earthworms before pupating in the soil and emerging as adult flies.

When temperatures start to drop, adult cluster flies will look for warmth and shelter by entering buildings through holes and cracks in exterior walls and around doors and windows. You can often spot them clustering indoors during the fall, winter, and early spring. 

What do they eat?

Unlike houseflies, adult cluster flies aren’t drawn to rotting or decaying food, and they won’t feed inside your cottage either. Instead, cluster flies eat things like flower nectar, fruits, and sap. So if you see them in your kitchen, that bunch of browning bananas isn’t the culprit. 

Where do they like to hide?

You don’t have to worry about adult cluster flies eating, breeding, or laying eggs inside your cottage. They’re just trying to spend the winter somewhere warm, which is why they nestle into walls, crawlspaces, and attics. And when the weather warms up in early springor in the winter, if your cottage is heatedthey may emerge to gather in clusters near windows and ceilings, trying to get outdoors.  

Should you be worried about them?

Cluster flies are fairly harmless; they don’t bite or spread diseases, and they won’t damage your property. But they can definitely be a nuisance when they’re swarming around your rooms in large clusters, and crushed cluster flies will leave a distinctive buckwheat-like odour and markings on walls, carpets and fabrics that may be hard to remove. Finally, the appearance of dead flies in your cottage may attract other unwanted pests, like larder beetles. 

How can you get rid of them?

An aerosol spray like Raid Mosquito and Fly Killer 1 or Raid Max Flying Insect Killer 3 can eliminate a swarm of cluster flies in minutes with doors and windows closed. A vacuum cleaner or fly swatter can also work well, but keep in mind that squashing them might leave a residue or stain on your walls or other surfaces. 

Ward off future infestations by sealing or caulking all potential points of entry into your cottage: holes in screens, soffit vents, cracks in exterior walls and around doors, windows, and baseboards. Be thorough; these little insects can squeeze through the smallest of cracks and crevices.