Cluster Flies

It’s easy to identify this pest by the “clustering” effect the flies have on walls and within light fixtures during the night. They are also known as “attic flies” because they hibernate in attics and in warmly kept structures throughout the fall and winter months, which is where the conflict with people comes from. 

You’ll begin to notice them flying in your home on days when it is noticeably warmer, this is when the flies are trying to return outside to reproduce but become confused and end up trapped in the structure.

Cluster fly

Cluster flies are slightly larger than the common housefly and have a golden sheen due to the gold hairs located on their thorax. 

Life Span

The lifespan of a Cluster Fly can be anywhere from a month to 50 days. This means there can be multiple generations in a season. 

Life Cycle

When Cluster Flies reach adulthood, they will lay their eggs in lawns, fields, or gardens. Within 3 days the eggs will hatch in the soil where larvae will find an earthworm to use as a food source and host till it reaches maturity. This stage can take around 2 to 3 weeks depending on how long it takes the fly to pupate. Once it has begun pupating, the process to become fully mature takes 11 to 14 days.

What attracts them?

Cluster flies can be attracted in three ways. First, your home is a warm structure in the winter months, which will attract the fly when it’s searching for a warm hibernation spot in the fall. 

Second, Cluster Flies are attracted to light contrary to other flies that are only attracted to filth and waste. During the day you might find the fly buzzing around a sunny window whereas at night you’ll most likely find them fixated on an artificial light source. 

Third, once a home has been marked by pheromones as an ideal hibernating spot the next generation will most likely come back and bring more flies than before. 

What do they look like?

They can be up to half an inch in size which is slightly larger than a common housefly. Their coloration is dark and light gray markings and if you look close enough, you can see the golden tint from the coarse hair that’s located on their backs. 

When the Cluster Fly is at rest, their wings will overlap, whereas Housefly’s don’t. To identify the larvae, look for a long wedged-shaped body that is completely white or somewhat cream-colored. In case you find eggs in your garden or in your yard, which are rarely seen, they will look like pieces of rice clumped together. 

When are they most active?

Because Cluster Flies are attracted to warmth and light, they’re most active during the day. Before winter comes, you might find a large number of Cluster Flies congregating near a hole on the sunny side of a house trying to find a hibernation spot. 

What can I do to keep them out of the house?

There is no way to keep out every Cluster Fly. One of the best ways is by frequently treating your home with the help of a pest control company that can create a chemical barrier. Treating the inside of your home is equally important, with the most important areas being window frames, utility pipes, and cracks that are large enough for small pests to enter. 

Considering earthworms host the Cluster Fly larvae, another way to prevent a potential breeding ground is to clean up any yard clippings or debris left in your yard. Keeping decaying organic matter away from your house will also deter eggs from being laid close to your home or other structures. 

Do they bite?

They do not bite humans or animals and are not known to carry around transmittable diseases. 

How do you find and eliminate breeding grounds?

To prevent eggs from being laid in the ground around your home it’s best to frequently treat the area around your house. Cluster Flies do not lay eggs in houses, so there’s no risk in finding larvae inside of your home. 

How fast do they multiply?

It takes around 30 days or shorter for the flies to reproduce, this means there can be around 3 to 4 generations of Cluster Flies in one season. 

What damages can they cause to my house?

These flies are only considered nuisances and will cause no damages to your house. The only thing they’ll leave behind is excreted matter or carcasses. If flies do die within the structure this can attract another pest called Larder Beetles. 

What are their feeding habits?

Cluster Flies do not have biting mouthparts, unlike horse flies or gnats. Their only feeding time is in their larvae stage once they have found an earthworm to burrow themselves in to feed on. 

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