April 2014 - Cluster Flies

Cluster fly infestation

It has been a warm spring and insects came out of hibernation early. Many ladybirds and queen bumblebees have been seen since the end of February. Small tortoiseshell and peacock butterflies, typically hibernating in roof spaces and out buildings have appeared in significant numbers. In our garden, there has even been evidence of a hedgehog rooting around for worms and slugs throughout the winter as it took advantage of the mild conditions, and decided not to go into deep hibernation. 

On Sunday 9th March the Bawburgh Wanderers chose Ringland for their ramble and I was privileged to join the group. It really was the most glorious day. Towards the end of the 'wander' we visited St Peter's Church in Ringland, and my eyes were immediately drawn to the vast numbers of flies that had accumulated on the window sills.  These flies are aptly named 'cluster flies' and they have the most extraordinary life cycle.

An alternative name for the cluster fly is 'attic fly' and I am sure that many of you have experienced these unwelcome insects sometime or other, as I have. They are similar in appearance to the common house fly although a little larger, with golden hairs on their thorax.  As the weather cools in autumn, the adults 'cluster' together, hibernating in roof spaces, out buildings, bird boxes and  holes in trees where they can remain relatively warm, living on their own fat resources. In the spring as temperatures start to rise they emerge en masse. Windowsills may be covered with their bodies as they attempt to get outdoors to feed. The adults lay their eggs in well-drained moist soil, in meadows or other places with grass covering. The larvae hatch and immediately start to hunt for worms. One or more larva will eat  their way into an earthworm and then feed on it until ready to pupate many months later back in the soil. If the host is killed prior to a larva being ready to pupate, it will hunt for a 'fresh' host worm to continue feeding. These flies do not significantly affect earthworm populations. They emerge as adults in warm weather in spring and summer feeding on all types of outside organic matter including plant sap, fruit, flowers and manure. Unlike other 'house flies,' cluster flies do not lay their eggs in meat and do not carry disease.



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