Description
Flies are the adult insects of the order Diptera and are characterised by having only two wings. The mouthparts of houseflies are formed into a proboscis for obtaining liquid food by dissolving the food with regurgitated enzymes allowing it to be sucked up. They go through complete metamorphosis from egg, the feeding and growing larval states, pupa and adult. In suitable conditions, the life cycle can be very rapid (as little as 10 days for houseflies) and therefore infestation can build up readily. Domestic flies are associated with poor hygiene and rotting organic matter, as that is where the eggs are laid, the larvae develop and from which the adults emerge and feed.
There are a number of species of flies that congregate in large numbers inside buildings in winter to hibernate. These are known as Cluster Flies. Eggs are laid outside in fields or on animal dung etc. and develop there. However, in early autumn, the adult flies are attracted to warm south and west facing walls of buildings. As the weather cools, they will push through the tiniest of cracks around windows, between roof slates or other gaps in the building to form large, clustering masses inside loft areas, pelmets, cornices etc., to hibernate.
On warm winter days, or if heating is switched on, the flies can wake up and fly around often accumulating in window areas as they try to return to the outside. Often only certain buildings or rooms will be affected, and invaded year after year.
Some carpet beetle infestations in historic collections have been shown to originate in cluster fly debris on window sills, loft areas etc., where they have not been cleaned up regularly.
