Invasion!

Up in Suffolk, my parents are desperate to know what has invaded their home. The windows of a bedroom, not regularly used, are covered in flies. In the morning they get the vacuum cleaner out and by the evening....... well it is time to vacuum again! The answer is the Cluster Fly, Pollenia rudis, similar in size to the house fly but with golden hairs behind the head and on the thorax, (which rub off easily). They are in the Diptera Order, what we refer to as True Flies, and are one of the 120,000 species that we have so far identified. They spend their summer flying happily around meadows eating pollen, nectar and other types of organic matter. When it gets cold in the Autumn they set off to find a nice warm and dry place to overwinter. Who can blame them? The problem is that they love attics, lofts and unused rooms. The next problem is that they overwinter communally - in huge numbers if it has been a good year for them. They will not feed in your home, or breed but they will leave a large amount of fly excrement. Every time the temperature rises in your house they start to get active and look for light - hence the numbers around the window. The best bit though takes place outside and underground. These little chaps go through a parasitic stage in their life cycle. Once the egg hatches the tiny larvae find earthworms. When they have come across their future host, they eat their way under its skin. They have to bury in leaving their spiracles (breathing holes) outside. Then they feed off their hosts living flesh as they  grow. When they are ready to pupate they fall off the earthworm and pupate in its tunnel before crawling to the surface to fly away. Back up in Suffolk it is going to be '2011 the Winter of the Vacuum Cleaner' because they are in for the duration. What is around the window will only be a very small proportion of what is innocently snoozing away in the attic. The good news is that this has been a great year for the Cluster Fly and its population has boomed, so next year it might not happen again........