Flies are insects pertaining to the order Diptera. This is a large order, containing an estimated 1,000,000 species, including the housefly, which is one of the most common pest. Although they are mostly regarded as pests, flies of the order Diptera have a major ecological role and are of great human importance. They are the most important pollinators after bees, fruit flies are used in research as model organisms and maggots of some fly species are used in medicine in order to clean wounds. As pollinators, flies are especially significant in wet and cold environments, as compared to bees, they need less food themselves and do not need to provide food for their young.
Description and distribution of Flies
Flies are adapted to aerial movement and are equipped with one or more pairs of wings. Their heads contain the antennae, the eyes and the mouthparts. Their thorax bears the wings and the halters which help balance the insect during its flight and the third segment is the abdomen which consist of up to 11 segments, depending on the species. Flies have a mobile head with a pair of large compound eyes on the sides of the head, and the houseflies have red eyes, and the slightly larger female has these set further apart than the male.
An adult housefly can grow to 8-12 mm (0.3-0.5 in) long, have a dark gray or even black color, six legs, a pair of wings and antennae. The whole body is covered with hair-like projections, making them really sensitive to the environment around them. They do not have a stinger, but in turn their mouths absorb food like a sponge. Their tongues are shaped like straws so they can suck up their food. They eat any wet or decaying matter, but they are particularly attracted to pet waste because the odor is strong and it is easy for them to find. They fly with great precision, having a flight speed of about 2 m/s (7.2 km/h), and the wings flap about 200 times/second.
There are four stages in the development of a fly. The eggs are white and about 1 mm long, each egg being elongated with bluntly rounded ends. Eggs occur in clusters of about 100. Within a day, larvae, also known as maggots, hatch from the eggs. They live and feed on dead and decaying organic material, such as garbage, carrion or feces. They are pale-whitish, 3–9 mm long, thinner at the mouth end, and have no legs. The life cycle of larvae ranges from 14 to 90 days and at the end of their fourth instar, the maggots crawl to a dry, cool place and transform into pupae, colored reddish or brown and about 8 mm long. Out of the pupae, the adult flies emerge, thus completing their metamorphosis. The adults can live from two weeks to a month in the wild, and after only 36 hours after emerging from the pupae stage, the females are receptive for mating. Normally, the female mates only once, storing the sperm to use it repeatedly for laying several sets of eggs.
Flies are often abundant and they can be found in almost all terrestrial habitats in the world apart from Antarctica. They include many familiar insects such as house flies, blow flies, mosquitoes, gnats, black flies, midges and fruit flies. From the total number of species accounted for, an estimated of about 19,000 species of Diptera can be found in Europe, 22,000 in the Nearctic region, 20,000 in the Afrotropical region, 23,000 in the Oriental region and 19,000 in the Australasian region. While most species have restricted distributions, a few like the housefly (Musca domestica) are cosmopolitan and thrive in your household. They like heat, so they are very comfortable at temperatures between 20-40°C, but at temperatures above 45°C every activity they have ceases. Flight, feeding, mating, and reproduction are put on hold at temperatures below 15°C as well, when the flies are entering a dormant state of “hibernation”, whether they are in their adulthood stage or in the pupae one.
Breeding and dietary information
Females lay their eggs in manure, compost, rotting food (biodegradable garbage) and manure mixed with straws. After an embryonic development of about 15-25 hours the headless and legless larvae hatch. By waving their body, they can move easily in the food substrate, without the need of any help, and they feed on the decaying substances found in the area where they are located. During this time they grow and molt twice, before passing to the pupae stage. The duration of the pupae metamorphosis achieved depends on the temperature around and takes up to 3-8 days. After leaving the pupae, adult flies are ready for reproduction 1-2 days after hatching.
Adult house flies live 2 to 4 weeks in summer and even longer in cool weather. In summer, a new generation can be produced every 8 to 14 days, but under unfavorable conditions as many as 20 days may be necessary. Ten to twelve annual generations are common. House flies usually overwinter in the immature stages, primarily as pre-pupae.
When if comes to their feeding, house flies feed on liquid or semiliquid substances beside solid material which has been softened by salivating or vomit. This is why water is an essential part of the diet of these flies, as they can not survive more than 48 hours without water. Flies also need food for at least two or three times a day. Because of their large intake of food, they deposit feces constantly, which is one of the factors that makes this insect a dangerous carrier of pathogens. They feed on any type of human food, on garbage, waste, excrements, animal dung, or sweat. The housefly is very dangerous for people as it can take over and carry various pathogens from the dirty places they come by, that are subsequently deposited on foods that we then consume. Flies are genuine transmitters of diarrheal diseases, skin and eye infections, tuberculosis, typhoid, cholera, polio. When you see a fly shaking their tiny, hairy legs, be sure that they are full of bacteria and germs collected from decaying matter, dung or feces, and they will now spread onto your food and inside your home.
Although they are domestic flies, usually confined to human habitations, they can fly for several miles from their breeding place. They are active only in daytime, and rest at night, at the corners of rooms, ceiling hangings, cellars, and barns, where they can survive the coldest winters by hibernation, and when spring arrives, adult flies are seen only a few days after the first thaw.
Due to the ability of housefly larvae to feed and develop in a wide range of decaying organic matter, they are important in the recycling process of nutrients in nature. Research also suggests that their adaptation can be exploited to combat ever-increasing amounts of waste, as housefly larvae can be controlled in a manner in which they could reduce animal manure, thus also reducing the bulk of waste and minimizing environmental risks of its disposal. Harvested maggots may be used as feed for animal nutrition as well.
Flies as pests
Depending on the species, flies can be considered both consumers or pray. The larvae can be herbivores, scavengers, decomposers, predators or parasites, with the consumption of decaying organic matter being one of the most prevalent feeding behaviors. The larvae of some groups feed on or in the living tissues of plants and fungi, and some of these are serious pests of agricultural crops. The species of flies that feed on vertebrate blood have sharp stylets that pierce the skin, inserting anticoagulant saliva and absorbing the blood that flows, also transmitting certain diseases in the process. Birds, bats, frogs, lizards, dragonflies and spiders are among the predators of flies.
Taking into consideration the housefly, the are a nuisance especially because they bother people by flying around and landing on them. However, they are most feared due to their ability to carry pathogens and transmit diseases, as advised above. They develop mostly in the warmer periods of the year, as they lay their eggs in the ground or on animal feces and when the temperature grows at the larvae hatch. They normally hibernate during the winter, however, they can be active in a smaller number in colder periods as well, especially if they have established themselves inside a warm house, as they usually take cover inside buildings when the cold comes.
In order to control their spread and prevent an infestation, several steps must be taken, the first being the correct identification of the species you are dealing with. As during their lifetime, a female fly can lay up to 500 eggs, a small problem can become a large infestation if not dealt with in time and correctly. Once you have identified the problem, the following steps can help you in reducing the risk of an infestation.
- Control moisture by fixing leaky taps and blocked drains where water can gather, as flies need moisture to live and multiply;
- Clear food debris and liquid spillages from food consumption and preparation areas, under kitchen benches and appliances;
- Do not leave standing water (in watering cans and pot plants for example) as this offers flies opportunity to feed and breed;
- Keep food covered at all times, as even crumbs can attract flies and encourage them to lay eggs nearby. Leftovers should be carefully covered up, as the fly’s contact with the food is a main cause of food contamination;
- Stay hygienic by keeping your bins, sinks and food areas clean;
- Cover entry points everywhere in your house by fitting fly screens to windows, keeping windows and doors shut at night and installing a fly killer unit;
- Keep bird feeders clean and remove bird food before dusk;
- Remove clutter from inside the house and the garden as messy areas can become a potential breeding site;
- If you have dogs, cats or other pets, priority should be cleaning their litter trays quickly, because their droppings are not only a source of food for the flies, but also a perfect an environment for laying eggs;
- Do not leave organic matter (animal or vegetable) to rot, as it becomes soft and moist, providing ideal conditions for the growth of larvae.
In case of an infestation, flies can be removed through several types of methods, depending on the size of the infestation. If prevention methods failed, and flies managed to enter your house, for a few individuals, sticky paper is quite effective. Fly food attractants used in inverted cones can also be used, as well as fly traps using ultraviolet lights. In case of a larger infestation, selective use of insecticides is recommended, however all nonchemical management strategies should be tried first. Sanitation methods, along with screens to keep flies out of the home, should be sufficient to keep the development of an infestation in check, as they should help reduce the number of adult flies and thus also prevent the development of newer generations.
For more details on how to prevent or manage such instances when you are forced to deal with several or multiple flies, and the additional problems they cause, check our related articles on ways to “Prevent infestation with Flies”, and “How to get rid of Flies infestations”.