If you have been seeing small flies or gnats in your kitchen, they're probably fruit flies. Fruit flies can be a problem year round, but are especially common during late summer because they are attracted to ripened or fermenting fruits and vegetables. Tomatoes, melons, squash, grapes and other perishable items brought in from the garden are often the cause of an infestation developing indoors. Fruit flies are also attracted to rotting bananas, potatoes, onions and other unrefrigerated produce purchased at the grocery store. This fact sheet will explain how infestations originate and how they can be prevented in your home or place of business.
Biology and Behavior - Fruit flies are common in homes, restaurants, supermarkets and wherever else food is allowed to rot and ferment. Adults are about 1/8 inch long and usually have red eyes. The front portion of the body is tan and the rear portion is black. Fruit flies lay their eggs near the surface of fermenting foods or other moist, organic materials. Upon emerging, the tiny larvae continue to feed near the surface of the fermenting mass. This surface-feeding characteristic of the larvae is significant in that damaged or over-ripened portions of fruits and vegetables can be cut away without having to discard the remainder for fear of retaining any developing larvae. The reproductive potential of fruit flies is enormous; given the opportunity, they will lay about 500 eggs. The entire lifecycle from egg to adult can be completed in about a week. Fruit flies are especially attracted to ripened fruits and vegetables in the kitchen. But they also will breed in drains, garbage disposals, empty bottles and cans, trash containers, mops and cleaning rags. All that is needed for development is a moist film of fermenting material. Infestations can originate from over-ripened fruits or vegetables that were previously infested and brought into the home. The adults can also fly in from outside through inadequately screened windows and doors.Fruit flies are primarily nuisance pests. However, they also have the potential to contaminate food with bacteria and other disease-producing organisms.
Prevention - The best way to avoid problems with fruit flies is to eliminate sources of attraction. Produce which has ripened should be eaten, discarded or refrigerated. Cracked or damaged portions of fruits and vegetables should be cut away and discarded in the event that eggs or larvae are present in the wounded area. A single rotting potato or onion forgotten at the back of a closet, or fruit juice spillage under a refrigerator can breed thousands of fruit flies. So can a recycling bin stored in the basement which is never emptied or cleaned.
These flies are commonly found throughout Europe and the UK the name refers to their habit of clustering together in large numbers and hibernating in buildings. There are several species found in the UK but they are often found in mixed swarms. The sizes vary between species from 3 to 8 mm, but the commonest species are 3 to 4mm long.
Life Cycle - Eggs are laid on damp soil or beneath dead and rotting leaves. The larvae of one species seek earthworms and bore through the body wall and are therefore more common in the country. When the earthworm dies the larvae bore out again and pupate in the soil. The adult flies feed on the nectar of garden and wild flowers. As a free-living insect the length of the life cycle is weather dependent. In Britain two generations are common, but in hot summers up to four are possible. During the summer and early autumn cluster flies are of no importance. As the season cools they seek shelter in nooks and crannies in houses and other buildings. When the temperature drops further they will seek greater protection and often form very large clusters in lofts or roof spaces. Often nuisance is caused by the presence of these large clusters outside buildings while they try to find a way in to hibernate. These masses may consist of several thousand flies clustered together. These large clusters produce a sickly smell. If the flies are warmed up during their hibernation they may emerge rather lazily and be a source of nuisance within the building. It has been observed that a single building in a row of apparently identical buildings will be selected for clustering year after year. This is no indication of poor hygiene standards and no explanation for the phenomenon has been found.
Blow flies and bottle flies are important scavengers in nature as they are one of the first insects to reach a dead animal. These flies are part of the decomposition process that recycles nutrients back into the soil. The maggots of these flies may be used by forensic entomologists to place the time of death in murder cases. They also breed in garbage containers, dumpsters, and decaying vegetative matter (e.g. compost piles). These flies are extremely common and can be found one to a few at a time in homes or businesses during the warm summer months. They are attracted to buildings by food odors and also warm/cool air currents emitting through cracks around doors and windows or through doors propped open for ventilation purposes. The sudden appearance of dozens of blow flies or bottle flies within a building signals a potential dead rodent, bird, or other animal in the wall, ceiling, attic, or crawl space. The Bluebottle is a member of a group of flies commonly referred to as 'blowflies' on account of their habit of 'blowing' or depositing their eggs on exposed meat. They are a pest of buildings where meat is to be found: slaughter houses, canning factories, meat processors and, of course, houses. Outdoors they are associated with decaying animal matter and rubbish tips. The female fly will enter houses with a loud buzzing noise, searching for flesh for depositing eggs on, or for food.
The Lesser house fly is commonly found indoors, especially males, which fly on irregular triangular or square courses in rooms, usually under pendant lamps. This fly is a major pest of poultry houses and farms where it breeds in manure and other semi-liquid organic matter. Although many species of flying insect are attracted to ultra-violet light emitted by electric fly killers, the Lesser house fly is not particularly attracted.
A worldwide pest of homes, shops, factories, catering establishments and rubbish tips. The adults are attracted to, and breed in, decaying animal and vegetable waste. The House fly is a major health risk: a carrier of a large number of disease organisms, e.g. Salmonella food poisoning and infantile diarrhoea. Active during the day and resting at night, preferring projecting edges high up in rooms as alighting surface.