Cluster flies in the loft.

Cluster Fly

What Are Cluster Fly

Pest-Tech often get called out to fly jobs. We carry out a survey and often identify the fly infestation as cluster flies. The common response from the customer is “what are cluster fly”. This blog has been produced to give you more of an understanding about Cluster Flies. We will be covering the following:

  • What does a cluster fly look like.
  • How they Reproduce.
  • Fly Behavior.
  • Why They Return To The Same Home.

What Does A Cluster Fly Look Like.

A Cluster fly is a 8 to 10 mm long fly, with a shifting pattern of silver and grey-brown markings on the abdomen. They have small patches crinkly gold hairs on the thorax and long wings. The larvae live as parasites inside earthworms.

Fly control in progress for Cluster fly | Pest Control Maidstone
Cluster fly found in the loft.

How They Reproduce

Eggs are laid in the soil and hatch in about a week. The young larvae bore into worms where they stay throughout the winter. In spring the larvae develop quickly, usually killing the worms, then pupate in the surrounding soil. The adult flies emerge in summer.

Fly Behavior

Cluster fly activity occurs inside buildings at the end of the summer. They bask on the side of the buildings, fences and walls catching the last of the summer sun. The flies have the habit of coming indoors in late autumn to hibernate during the cold winter months. This is normally in roof spaces and lofts. They first get into the property via crack and crevice from the gaps in the tiles.

Once inside the building they settle down for the winter. They are often found in groups or clusters of many hundreds or even thousands of flies. They congregate in roof spaces and dark corners of attics and little-used rooms. The flies also enter sash window boxes, cracks round window frames and unused Venetian blinds or curtains.

Occasional warm days bring the cluster flies out of their hiding places and they crawl or fall into rooms, often covering windowsills with buzzing flies spinning round and round in uncoordinated attempts to fly. In the following spring, the flies start moving again, and the problem recurs. The appearance of these lethargic flies causes considerable annoyance, although they are quite harmless.

Up lighters protruding into the loft or putting on the central heating can have the same effect. The warmth of the lights or the housewarming up, can cause some of the flies to awaken. This is when you get a slow trickle of flies appearing in the house.

Fly Control to deal with the cluster fly
Cluster fly overwintering in a loft

Why They Return To The Same Home

Although we know why clustering flies seek shelter in this way, we do not know why they enter certain buildings in preference to other adjacent or nearby properties. However, once a building has been invaded, it is almost certain that more flies will return in subsequent years. This is due to pheromone and scent from previous visits.

If you are having a problem with flies in your building or home then you may have a cluster fly infestation. If you would like help with this then we can help. More information on our fly treatments can be found here.