Information About Flies
Flies date all the way back to the ancient world and the time of Moses with depictions of flies on hieroglyphics from Egypt. However it wasn’t until the 17th century that scientists began to study the fly and later realized and proved that maggots did not magically appear in decaying flesh but rather that the eggs were actually laid in those places as a preferred breeding ground. More recently, flies have been taken aboard the space shuttle in efforts to study their behavior in weightless environments. Nowadays, they are considered to be one of the most common pests associated with people and as such are frequently found in homes and workplaces.
Flies are very common and there are approximately 120,000 different species of flies ranging from big to small, harmful and harmless. In the northeast United States, one may encounter species of flies known as the Fruit fly, Drain fly, Fungus gnat, Blow or Flesh flies, Black Soldier flies, Cluster flies, Stable flies and most common to homes in the New York area, the House fly.
Most of the flies one would encounter in their home are simply nuisance pests. With rare exception, flies don’t bite and none of them sting. However, there is proof of them being harmful to the point of spreading bacteria and diseases or the pathogens that lead to disease. Flies tend to prefer to live in what most humans would consider filth – i.e. decaying flesh or bacteria, rotting food, garbage cans, and manure – and as a result come in contact with many pathogens. Although it is unlikely, a single fly landing on a piece of food can potentially contaminate the entire object with a harmful disease and should therefore be considered a potential risk.
Classifications, Types & Anatomy
Flies belong to the insect Order Diptera and have two wings, as it implies: “di” means two and “ptera” means wing. Most commonly, insects will have two pairs (4) of wings (e.g. bees) but any insect with two wings is classified as a Dipteran; some of the more common pest-fly families within this order are Muscidae, Calliphoridae and Sarcophagidae.
Each fly is categorized into different species based on their distinct anatomical structure but all flies have the same basic features. Aside from having 2 wings, flies have six legs, three distinct body sections and two antennae – just like all other insects.
Most flies are small, and shaped for the needs of aerial movement, typically ranging from 1/10 to 7/10 of an inch in length. All have 3 distinct body sections: a head, a thorax and an abdomen. On the head are two compound eyes, two antennae and in some cases ocelli, which are light-sensing organs. On the front of the head is the non-chewing mouth, which is only useful for consuming liquids. The section of the body directly behind the head is called the thorax, which contains all of the muscles needed for locomotion (flight and walking) as well as a pair of wings and six legs. Also on the thorax are a pair of ’halteres,” which are actually highly reduced wings that function as a gyroscope, helping the fly balance itself during flight.
The abdomen is located behind the thorax. It contains the gut, which is of course used in the digestion of their liquid meal.
From the eggs hatch worm-like larvae or maggots. They have no distinctive legs or body segments.
House flies, Musca domestica, are generally ¼ of an inch long, but less than 3/8 inch, and are easily identified by the four dark stripes extending down their back (which is helpful in separating it from the Flesh or Stable fly, with which it is commonly confused). They are light grey with red-brown compound eyes. The larvae are cream colored with a blunt, or flattened, posterior end, coming to a point at the head. The pupa is oval and chesnut-brown in color.
Blow flies are in the Family Calliphoridae. These insects have a distinct metallic coloring (blue, green black, copper, etc.) to them and are generally ¼ inch long. The black Blow fly has is darker, with an olive-green hue on its body. In some instances the blue Blow flies are metallic blue to black or even purple and the green can sometimes resemble a bronze tone.
All blow fly eggs are white or pale yellow and are about 1/20 of an inch long. The larvae are also white to yellow and have pointed heads ranging from 2/5 to 4/5 inch in length. The pupa develop in a light-brown to black hardened case and are approximately 3/10 inch long and shaped like a football.
Flesh flies are in the Family Sarcophagidae and are sometimes confused with the House fly. The distinction between the two is easily made with the three black stripes down its back (the house fly has four stripes). The tip of the Flesh fly abdomen is red. The maggots are slow and sluggish.
Drain flies are also commonly referred to as Filter flies, Moth flies or sewage gnats. They are approximately 1/10 inch long, with a dark gray body and wings. They are one of the more ‘hairy’ species of flies.
Stable flies, Stomoxys calcitrans, are also called the “biting fly” as it is one of the few fly species that may actually ‘bite’. They have a proboscis that extends from the mouth, which is used for ‘biting’ and eating. They do not have four stripes, like the House fly which is commonly mistaken for a stable fly, and their abdomen is checkered.
Black Soldier flies, like its name implies, is black in appearance, reaching about 5/8 inch in length. It has two translucent spots on its back and looks much like a wasp.
Fruit flies are about 1/8 inch long. The most common of the Fruit Flies has bright red eyes, with a tan front half of the body and black towards the back.
Fungus gnats are about 1/10 of an inch long. They have dark-colored antennae and are generally gray to black in color. They have a distinctive vein pattern in their wings and their antennae, which are just above the eyes, are longer than the head. The larvae are oval, smooth and white as well as somewhat transparent.
Cluster Flies, Pollenia rudis, are also known as ‘attic flies’ and in some areas are more common to homes than House flies. They are large and black with short, golden hairs on its midsection under the wings. The larvae have a cream color and are shaped like a wedge.
Lifecycle, Breeding & Feeding Habits
Flies, like many insects, undergo complete metamorphosis when developing from immature insect to adult.
The eggs will develop in short time, approximately 8 to 24 hours after being laid, which is usually on or near the larval food source. (In some instances, development occurs so quickly that the eggs will hatch while still in the mother. This is known as ovoviviparous development.) Emerging from the egg, larva, or “maggot,” begins to eat immediately. Upon completing the larval stage, the maggot will shed its last layer of skin and enter the final, pupal stage of development. Once opening the puparium, the adult fly emerges. The flies body juices will pump through their wing veins,, allowing them to expand and dry so the adult can fly. They will begin to procreate almost immediately, just one to two days after they enter the adult stage.
There are a number of factors that will determine the length of time it will take to fully develop and how long a fly will live. Weather is a big factor and flies prefer warmer weather, producing their greatest numbers in the summertime. The entire lifecycle in some cases can take as little as 7-10 days from egg to adult. In other situations it can take 3 weeks. Flies may live as an adult for only seven days during the winter but may survive more than a month during the summer. During their lifetime, females can lay hundreds of eggs. This helps her to fulfill one of the fly species’ two primary purposes: to mate and to find new food sources.
Fly anatomy is unique when it comes to reproduction. Not only do flies have faster reproductive rates than most other insects but the female genitalia in some flies are rotated. This process places the reproductive organs in a position that will allow the males easier opportunity to mate with the female. When it is a permanent rotation, the change comes about during the pupal stage, but when it is temporary, it is done while mating. This characteristic, combined with other aspects of fly behavior results in flies having very high reproductive potential. From a practical standpoint, it means that pest species can become a problem overnight.
Flies are attracted to organic materials and waste. Some prefer decaying animal flesh, while others, such as the Phorid fly, prefer decaying organic material in drains and grease traps. Some species prefer fecal matter while even others prefer blood or nectar. The variety of foods that they will consume is very broad.
Flies do not have chewing mouthparts and therefore cannot eat solid foods. They will typically search for liquids to feed on, like nectar from fruits or blood from animals and humans, and use a variety of their mouthpart design to feed on these liquids. In some instances, flies will salivate on food, liquefying any solid nutrition in order to lap it up.
House flies prefer warmer temperatures (80° F) for breeding but will do so indoors year-round if the unsanitary conditions they require to breed are present. They will lay batches of eggs every 3-4 days, become an adult in less than 10 days after hatching, feed on fecal matter or decaying food and depositing their eggs in that material. They will typically live for three weeks in the summer but can survive up to three months. They require water in order to be able to produce saliva that will be regurgitated on the solid food they wish to eat. This will liquefy the food so that they can sponge up their meal. House flies actually taste their foods with their feet, which are 10 million times more sensitive to taste than a human tongue, and are attracted to unsanitary conditions, specifically large amounts of trash.
Blow flies are primarily attracted to decaying animal flesh, “carrion,” and fecal matter and typically lay their eggs on animal carcasses. The maggots will migrate to the top layer of the soil for shelter while they pupate. They will become adults within 10-25 days after hatching. The blow fly female can deposit thousands of eggs in her 2-8 week lifetime, as each batch of eggs may contain as many as 1,000 eggs or as little as 40. There may be as many as four to eight generations of Blow flies produced in a year.
Flesh flies, like Blow flies, also lay their eggs in recently deceased animal flesh. They also will lay their eggs in wounds, a condition known as myiasis. As a result, they have developed the name “flesh” fly. They will only infest a carcass for 5-10 days before looking for a new food source.
Drain flies reproduce in moist organic waste, typically the kind found in algae in drains or pipes. They can survive hot water and soap.
Stable flies use their mouthparts to pierce the skin and sponge up blood, which is their preferred food source. They will feed approximately once per day, usually on animals, although sometimes on people. (They prefer the meaty parts on the legs and lower body of horses and cows and the ears of dogs.) Once they eat they will move to a secondary site to digest the blood meal. Compost piles and freshly cut grass will provide suitable breeding sites for this species near their animal food sources.
Black Soldier flies will eat a variety of decaying organic matter, from vegetables and fruits, to feces and carrion. It will take around 4 days for their eggs to hatch in warm weather; larval stages can last up to 45 days; adults will live typically for 15 days; they will have around three generations per year. Mated females will die shortly after depositing their eggs.
Fruit flies prefer the fermenting fruit and vegetables as food sources and breeding grounds. Fruit flies exhibit high reproductive potential. Like the house fly, they will also feed and breed on garbage, drains and empty bottles – all they need is fermenting materials.
Fungus gnats, as the name implies, feed on the fungi associated with decaying or over-watered plants. They will breed in organic materials, such as piles of leaves, and complete their lifecycle from egg to adult in four weeks and live as an adult for 7-10 days.
Cluster flies overwinter in houses, exiting the structures in the spring so that they can mate, producing around four generations per year. They will not reproduce indoors, instead preferring soil to deposit their eggs, where their larvae develop inside earthworms, which they feed on. Their lifecycle takes 4-5 weeks to complete.
Environments & Activities
Flies will tend to stay within 1-2 miles of where they are born (although some have been known to travel up to 20 miles to find some food). They are usually hatched and develop near their food sources, so there is little need for them to travel much further unless the food source is depleted or a new one is required for a different reason.
There are two activities that a fly will focus on each day: mating and foraging for food.
Most flies tend to mate near their food sources so that the female can deposit the eggs in an environment in which the maggots will have easy accessibility to the food. These breeding / food source sites tend to include garbage cans, decaying animal flesh and carcasses, manure, fermenting fruit and vegetables, sewers and any other place decaying organic material is found.
Aside from those materials, some flies also enjoy feeding on blood and nectar. There are also many species that help pollinate flowers. Meanwhile, flies have to avoid predators such as dragonflies, spiders, birds and other flying insects.
Flies are typically found outdoors during the warmer summer months, but will otherwise migrate indoors to warmth and shelter from the cold. It is at this seasonal activity that makes them more of a nuisance in homes and workplaces.
House flies have historically been associated with human activity, and thus it is its common name.
Blow and Flesh flies, when found in large numbers inside, it may mean that an animal, such as a rodent, has died nearby. This often occurs in chimneys, ceilings, and wall voids.
Drain flies get their names as they are commonly found in drains feeding off of decaying organic materials. They are not great flyers and tend to crawl from place to place, flying only a few feet at a time, in a jerky motion. If they are found outdoors, it will typically be in a dark or shady area near standing water. The larvae, pupae and adults of this species are considered semi-aquatic.
Stable flies normally start to appear around stables during mid-spring and are usually only found in neighborhoods with livestock.
Black Soldier flies will usually appear in the summer months with temperatures above 80° F and will likely only be found in vegetation near livestock.
Fungus gnats are commonly found above the plantation of greenhouses, the Fungus gnat enjoys moist conditions, is attracted to light, is known to be a weak flier, and may be seen throughout the year indoors and outdoors. It often infests over-watered house plants.
Cluster flies their name comes from their habit of clustering together; in the northeast, they are usually found in south-facing wall voids or attics. Cluster flies are usually found outdoors after Autumn but find over-winter shelter indoors.
Dangers & Effects On Humans
Flies are generally harmless and a nuisance pest – nobody wants them buzzing around. However, there are some species that seek blood meals and can bite their victims. Additionally, many flies are contaminated with disease pathogens as a result of their preferred breeding grounds, enabling them to transmit diseases through contact with humans or human food.
Flies are capable of infecting open wounds on humans and animals and are known to spread over 100 different disease-carrying germs and at least 65 diseases. In most cases, the danger is present when flies land on pieces of food or on an open wound, during which time they may be transmitting pathogens, potentially endangering the unsuspecting human or animal.
Some flies are capable of damaging plants. Some flies may leave spots on windows and walls.
Control & Treatment
It is not easy to control a fly infestation once it breaks out. Prevention through good sanitation is the most effective control for most flies although if necessary, eliminating or controlling the species during the larval stage is the best treatment method. Chemicals are not the best approach as they are harmful to those around and because flies reproduce so rapidly, they will quickly become resistant to chemicals. Always consult a professional pest control provider, such as Assured Environments, prior to using chemicals to treat flies or any insect or pest. Chemicals should only be used in a last resort. There are several exclusion methods that should be tried first to control infestations, particularly with flies.
Place screens on all windows and doors. Seal any cracks, crevices, holes, or fill in the spaces where pipes lead into the structure, using expanding foam or caulk. Make sure proper sanitation is maintained throughout the structure, indoors and outdoors, on a daily basis. Clean drains and trash chutes and compactors on a routine basis. Tightly seal trash, grass clippings, organic waste, or any other materials that flies may be attracted to.