Cluster Flies

What Are Cluster Flies?

Cluster flies are a common yet often misunderstood insect that can become a nuisance in homes, especially during the autumn and winter months. Unlike house flies, cluster flies are not attracted to garbage or food waste. Instead, they are primarily outdoor insects that find their way indoors as temperatures drop. 

Types of Cluster Flies

1. Common Cluster Fly (Pollenia rudis): Larger (8-10 mm), dark grey with golden hairs. Commonly invades homes in autumn to hibernate. Larvae parasitize earthworms.

2. Lesser Cluster Fly (Pollenia pediculata): Smaller (3-5 mm), dark grey with faint golden hairs. Exhibits similar clustering behavior but is less noticeable due to its size.

3. Yellow-Cluster Fly (Pollenia amentaria): Slightly larger, with a yellowish hue from denser hairs. Often found in rural areas, they seek shelter in homes during colder months.

4. Green Cluster Fly (Pollenia viridana): Metallic greenish tint, around 4-6 mm. Less common but still invades homes to overwinter. Similar lifecycle, targeting earthworms.

5. European Cluster Fly (Pollenia angustigena): Slightly silvery, similar in size to P. rudis. Prefers rural areas and invades homes for winter hibernation.

All species enter homes in autumn to hibernate, gathering in attics and wall voids. While not harmful, they can be a nuisance due to their clustering behavior.

The Life Cycle of Cluster Flies

Cluster flies have an interesting and unique life cycle. Their larvae develop as parasites inside earthworms. During spring and summer, adult cluster flies lay eggs in the soil. When the eggs hatch, the larvae seek out earthworms, entering their bodies and feeding on them. This parasitic stage is crucial for their development. Once fully grown, they emerge as adult flies.

In late summer and early autumn, adult cluster flies seek shelter to hibernate through the winter. They are drawn to the warmth of buildings and often enter through cracks, gaps, and small openings in walls, windows, and attics. Once inside, they gather in large groups in attics, wall voids, or unused rooms, hence the name "cluster flies."

Why Do Cluster Flies Enter Homes?

Cluster flies invade homes primarily for hibernation. As temperatures drop, they look for a safe, warm place to overwinter. They are particularly attracted to sunny sides of buildings, where they can find small cracks and crevices to squeeze through. Homes in rural areas or near fields are more prone to cluster fly invasions due to the abundance of earthworms in the surrounding soil.

Unlike common pests, cluster flies do not breed indoors. They do not infest food or cause damage to furnishings. However, their presence can still be a significant nuisance, especially when they emerge from hibernation on warm winter days or early spring.

Are Cluster Flies Harmful?

Cluster flies are not harmful to humans or pets. They do not spread disease, bite, or damage property. However, their presence can be bothersome, particularly when large numbers are involved.

How to Get Rid of Cluster Flies

If you already have a cluster fly infestation, there are several steps you can take:

1. Vacuum Them Up: One of the simplest methods is to use a vacuum cleaner to remove flies from windowsills, walls, and other surfaces. This is an effective way to deal with small numbers without using chemicals
   

2. Foggers and Aerosols: In severe cases, aerosol sprays or foggers designed to kill flying insects can be used in attics or enclosed spaces. However, these methods should be used with caution and according to the product instructions to ensure safety.

3. Professional Pest Control: For larger infestations or recurrent problems, it may be best to call us for a professional pest control service.

The best time to treat for Cluster Flies is from December to February but if they are becoming a nuisance in Autumn they can be treated to reduce the population but will most likely need a second treatment in late Winter as the flies will have continued to enter the building after the Autumn treatment until the weather gets cold.

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