Why Are There So Many Flies In My Apartment all of a Sudden?

Apartments are a great housing solution. However, they are not perfect. They often pose several problems that are unique to them, not least of which is household pests like cockroaches, bedbugs, rats, flies, and more getting transferred from unit to unit.

Flies are a major problem in a lot of apartments. They love areas with high human populations, such as apartment complexes.

This article will take a deep dive into this phenomenon and explain why you may have experienced a surge in the number of flies in your apartment. Having lots of flies in your apartment is not only irritating but may be misconstrued by guests as having poor hygiene standards. The good news is that understanding the type of fly problem you have, the seasonality, the habits, and the lifecycle of different fly species can help you to identify the most effective prevention and control method for your unique problem.

Types of flies

Around the world, flies are a very common pest. This is because of their ability to reproduce in large numbers, and the high speed with which they reproduce. Typically, a female can lay 75 to 150 eggs at a time around the home, mostly in excrement, garbage cans, compost pile, and other rotting material. Unfortunately, these eggs are difficult to spot with the naked eye.

As a common characteristic, all flies undergo four stages of development. It all starts with the egg getting laid and hatched, which then turns to a larva, then a pupa, and finally an adult.

The different types of flies and their distinct characteristics include:


This is the most common type of fly found in houses hence its name. The adult flies are identified by their gray to black color, slightly hair bodies, and a single pair of membranous wings. They also have red eyes with four dark longitudinal lines on their thorax.

In her lifetime, the female can lay up to 500 eggs. However, the mating happens only once each time with the female storing the sperm from the male. The eggs are white and are deposited in dead or decaying organic matter such as feces and food waste.

 In a day, the eggs hatch into larva and feed on this decomposing organic matter. These will appear as legless and pale whitish. Depending on the conditions present, larva development to the pupa stage may take two weeks to a month. 

The optimum conditions are usually high temperatures hence infestation is likely to occur during the summer days. However, the larva avoids direct light and prefers to feed in a warm, dark and moist place.

Before their metamorphosis to the pupa stage, the larva crawls to a dry and cool place. If the conditions are still favorable, development to adulthood may take two to six days. High temperatures too, do favor the faster development of the pupa.

In the adult stage, the lifespan is anywhere from two weeks to a month. However, the sexual development occurs within 16 to 24 hours of being adults. Adults also feed on dead or decaying matter and can carry food-borne illnesses such as typhoid, tuberculosis, and salmonellosis. This happens if they settle down on your food having carried these pathogens on their legs or mouthparts.

The major sign to indicate their infestation is the appearance of a larger swarm of the adults flying about. Larvae can also be detected as they crawl out to pupate.

Fruit Fly

As the name suggests, fruit flies are normally attracted to ripe, rotting, or decayed fruits. They are a common pest in places where food is served such as homes and restaurants. The fruit fly is yellow-brown with brick-red eyes.

To develop at a faster rate, fruit flies require warm temperatures and crowded places, with the shortest development time from egg to adulthood being only 7 days. The female lays up to 400 eggs into rotting fruit or vegetables. Interestingly, the mother inserts her fecal material to the egg sac so that the larva gets a composition of what to feed on before they are hatched.

 The eggs hatch after only 12 hours into a larva that feeds on the microorganisms responsible for rotting the fruit as well as the sugars on the fruit. At room temperature, 25 degrees Celsius, the larva undergoes metamorphosis to the adulthood stage within four days.

After only twelve hours of emerging from the pupa to the adult, the fruit fly is ready to mate and reproduce the next offspring. This is done by the male depositing sperm to the female’s abdomen later used to fertilize her eggs.

While the risk of spreading disease is low, fruit flies can pick harmful pathogens as they feed on the rotting fruits. To avoid an infestation it is recommended you store away the fruits in your household in a cool and dry place.

The major signs of a fruit fly infestation are the presence of adult fruit flies flying around inside the house or the trash can where rotten fruits have been disposed of. The pupa may also be found in dry places and mostly beside decaying matter. The pupa resembles a cockroach or even a rodent dropping.

Drain fly

These are also known as sewer flies, filter flies, or moth flies. They have short, hairy bodies and wings giving them a furry moth-like appearance. When crushed, they leave a powdery smudge. Most species are found in warm and humid places and reside in plumbing or sewer systems.

The female lays 30 to 100 eggs just above the water lines inside most drains that are sludge-based such as bathroom sinks. These eggs hatch into larva known as drain worms due to their thorax being larger than their abdomens. This happens within 48 hours.

The larva then feeds on the bacteria. While they may be problematic in large numbers, smaller numbers however can help unclog drains as the drain worms use their strong jaws to cut through the hair and sludge found in drains.

During the pupa stage which lasts between 20 and 40 hours, the insect is submerged near the water’s surface and does not feed. The adults then emerge and are usually nocturnal attracted to light and odor.

Even though they come from drains, drain flies are usually not harmful to humans. However, getting rid of a swarm of these flies is usually hard to do physically. This is because they are water and bleach resistant therefore the only option remains to ensure the drains are kept clean for periods lasting up to three weeks. This can be done by using high pressured water to clear off sludge used by the larva to feed.

The common signs of a drain fly infestation include having adult flies resting near drainage systems such as the kitchen or bathroom sinks. Larvae can also be spotted crawling about in breeding material.

To identify the breeding sources in suspect drains, you can cover this in clear plastic bags coated with petroleum jelly or even vegetable oil.


These are also referred to as horseflies and develop well in warm areas. They are tiny insects with a hairy appearance, long stilted legs, and large black eyes. Their wings are held above their body in a V shape position. They are blood-sucking insects.

The female sand flies are known to suck blood from mammals, birds, and reptiles. However, unlike other blood-feeding insects, the sand fly prefers to feed during the day and is inactive at night. The protein in the blood is necessary for egg production. The female produces 30 to 70 eggs at a go and lays them in cracks or holes in buildings or even burrows used by other animals.

As they are blood-sucking insects, a bite from them is usually painful and may cause a blister or a red bump. If not taken care of, these can cause an infection. Hydrocortisone applied to the wound usually helps to heal and reduce itching.

The number of sand flies that develop into adulthood is severely affected by weather with the lowest numbers being during the cold seasons. For the larva to develop, cool, dark and humid places are preferable. The total life span of a sand fly is usually a month to three months. 

Adult male sand flies normally feed on nectar and have weak mouthparts. It is only the females that feed on blood. As they feed on blood, sand flies are known to transmit diseases to humans such as sandfly fever.

Sand flies are way too small to be seen with the eyes; therefore a sand fly infestation may be hard to spot.

Flesh flies

These are identified by their red eyes, gray and black longitudinal stripes on the thorax, and a checkered abdomen. Unlike other flies, the female does not lay eggs but rather produces hatched maggots on decayed flesh, dung, or even open wounds of living animals. Some larvae are even known to be internal parasites.

In a season, the female can produce 300 larvae known as tykes. The larvae then gorges on the dead and decaying flesh before moving into the soil to pupate. The pupa then takes 10 to 15 days to mature into adulthood.

The adult flesh fly can reproduce a day after its full maturity to repeat the life cycle all over again. Adults then feed on fluids from animals, sweet foods, fluids from animal waste, and other available organic materials.

Flesh flies are known to be dangerous to human beings as they carry the bacteria responsible for leprosy.  If the apartment is surrounded by large accumulations of pet feces, exposed trash cans, or poorly maintained compost heaps, these may be a perfect breeding ground for flesh flies to suddenly appear.

Cluster flies

These are also known as attic flies. This is because, during the cold season, these flies seek shelter in warmer darker places such as the attic. The female lays eggs outside in earthworm burrows where the larva being parasitic, then feed on the earthworms.

These flies are recognized by distinct lines behind the head, short golden hair on the thorax, and dark and light gray areas on the abdomen.

Once laid, the eggs hatch after 3 days and the larva bores into an earthworm for food. The larva feeds off its host for a period of 2 to 3 weeks before it pupates. After another two weeks of development, the adult emerges.

Adult cluster flies are slow-moving and are not harmful to humans. However, they can be a bother and viewed as pests when they invade the home. This happens normally at the beginning of the cold season. Looking for somewhere to hibernate, cracks, and crevices in windows do serve as an entry point into the house. Other openings such as unscreened vents also offer a way in.

Once inside, the cluster flies amass together in warm dark places to hibernate for the winter. As they migrate indoors in cold conditions, a major sign of their infestation is the spotting of this flies in the attic or other dark storage spaces. As they are hibernating during this cold time, the insects will also appear as lethargic and slow-moving.

Black flies

These are also biting insects that feed on blood from animals. As they feed on human blood too, they are a common nuisance. While the male does not bite, flying in large swarms, they can enter into exposed orifices. Their appearance is normally black or gray, small and with short antennae and legs. While males feed on nectar, the females feed on blood before laying eggs.

The eggs are laid on running waters and the breeding success depends on the levels of population in the water. Once hatched the larvae attach themselves onto rocks and feed on passing debris in the water. The larva then pupates underwater before emerging in a bubble of air as flying adults.

Adult females can travel up to 60 kilometers in such animals to bite for blood. As the females fly in large swarms, bites from these insects are extremely painful and result in painful lesions. Most often the bites require medical attention.

Bites from these flies occur in areas with thin flesh such as the neck, arm, or ankles. This may be lethal to human beings as they are known to cause river blindness disease. This is often accompanied by headache, nausea, and swelling of the lymph node.

Globally, this is the second most common cause of blindness after trachoma. Major signs of infestation include large swarms of the flying insects noted by their appearance.

Controlling the infestation of these flies

While most of the flies may look somewhat the same, methods for controlling their infestation vary widely. However, the majority of these flies do breed and infest during warm seasons, which means preparing yourself early enough is the key to controlling them.

Controlling your housefly infestation may require a complete overhaul of your sanitation measures. It involves disposing of food waste and other decayed organic materials in vacuum-sealed plastic bags to prevent the female flies from laying eggs and generally maintaining high standards of hygiene inside the apartment.

While killing adult flies may act as a deterrent, removal of potential breeding ground is more important. As for the adult house flies, common methods such as the use of fly traps may help to kill them. These fly traps are usually infused with insecticides.

To control the infestation of fruit flies, fresh fruits should be refrigerated. Other than that, proper sanitary measures should be observed when disposing of rotting or damaged fruits as well as fermenting vegetables. Cleaning of garbage cans should be done regularly.

For a drain fly control program, removing the breeding grounds is essential. This involves cleaning regularly all drainage areas. If you visit the stores, inquire for bioproducts that may eat the organic materials inside the drains required for breeding.

Sand flies are hard to detect because they are small. However as sandflies usually leave a painful bite, the use of insect repellant is highly recommended.  Using recommended insecticides sprayed on cracks and crevices may also work to prevent infestation.

Getting rid of stuff that attracts flesh flies is the first step in controlling them. These may include carcasses of animals around the apartment such as dead rats and mice. Pet waste also forms a major breeding site so these should be disposed of in plastic sealed bags.

If your apartment is infested annually by cluster flies you may use repellant that releases a fragrance which the flies may find as unpleasant. This can be done by hanging out a wick that releases the odor found to be pungent by the cluster flies.

While black flies may not breed in the household, they generally affect buildings close to waterways. Therefore using screens in building openings such as windows and vents ensures that these flies stay away.

Final thoughts

Identifying the flies and seasons in which infestation may likely occur around your apartment can go a long way in helping you figure out what remedies to use to control them. At the end of the day, though, there is no one solution to getting rid of all types of flies entirely. However, when you follow the tips and tricks outlined here, you will be one step closer to alleviating your pest problem.

Melanie Asiba

Melanie is an author, and she enjoys traveling, reading, and trying out new things. In addition to writing for Apartment ABC.

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