Cluster flies can become an issue around autumn as they will typically they will start to gather in large numbers. Often, they will cluster around windows as they are attracted to any form of light during the day, but they will then tend to move and hibernate in roof spaces at night.

This means that even if you only spot a few, the chances are there will be more, and you could have an infestation somewhere in your home. In the autumn, cluster flies will often gather in large numbers on sun-warmed walls during the day. As the cooler temperatures arrive in the evenings , they will crawl into crevices or under the eaves and fascia’s or into the roof spaces and may start to gather in lofts or wall voids or any undisturbed areas where they can eventually hibernate safely in the warmth over the winter.

The common cluster fly is large and black, these flies can be easily mistaken for house flies. The difference is their yellowish golden hairs on the thorax and a prominent dark and light-coloured chequered pattern on their abdomen. And they tend to be sluggish in flight. There are a few other cluster fly species that are slightly different in size and colour, but the common cluster fly is the one you’ll be mostly likely to encounter in the loft space.

Once the weather warms in the spring, cluster flies start to become active again. Although, because of our temperature-controlled homes, it’s not uncommon for them to emerge earlier having been tricked into thinking spring has arrived. The adult flies will eventually leave in late summer to lay their eggs in the soil. The cluster flies’ larvae are parasitic so feed on earthworms and will then pupate in the soil, eventually emerging as adults ready to find shelter for the winter months.

Although these insects don’t bite, they’re considered a nuisance because of the amounts in which they migrate into a property to hibernate over winter. Naturally, we don’t want to share our property with swarms of cluster flies and for a business, it’s not great if noticed by customers either.