There are thousands of different species of fly in the UK, but many are found in the wild and do not come into contact with humans. The common fly pest species are the Cluster Fly and the Housefly. During summer and early autumn Cluster flies are no problem and go about their business without coming into contact with humans, but towards the end of the autumn they seek out likely places to spend the winter. If they did this in small numbers the Cluster fly would not be considered a pest, but unfortunately this is not the case, and they can sometimes be found in vast numbers in one loft whilst the neighbours on either side have none. Large numbers often produce a stick smell. On warm, sunny days, the flies often emerge from their hiding place and swarm on windows causing great annoyance by their buzzing and by their presence. Dead flies provide a food source for the larder beetle and can contribute to the presence of other nuisance insects in the house. Houseflies are a health risk and can spread diseases such as food poisoning and dysentery.