In biology, fly is a typical “complete metamorphosis insect.” In the late 1970s, there were more than 120,000 species of 132 species of Diptera in the world, including 64 families and more than 34,800 species of flies. The main species are housefly, city fly, flies, and flies.


In the ecosystem, the larvae of flies play an important role as decomposers of plants and animals. Adults of flies can also be used for pollination and variety improvement of crops instead of bees because they are fond of sweet substances.

Population distribution

Distribution all over the world.

Morphological character

The flies belong to Diptera. They are small to medium-sized. Their antennae are shorter than the total length of the head and chest. They have only three segments. At the end of the terminal segment, there is a knot whip or a feather on the back of the terminal segment. They are called arista. There were 2 compound eyes and 3 single eyes. The mouthpiece is suction-licking. Anterior wing membranous, used for flight. The hind wing degenerates into a halter, concealed beneath the base of the forewing.

Not Infected by Bacteria

Flies have a unique digestive tract. When they eat food with a variety of pathogens, they can be quickly processed in the digestive tract, quickly ingest nutritious food and timely discharge useless dregs, wastes and pathogens out of the body. This process takes only 7 to 11 seconds, so most bacteria are excreted from the fly before they can reproduce.

Detailed explanation of species

Flies are distinguished from other insects by their predecessor wings developed and their hind wings degenerated into balance sticks. The head has a pair of round compound eyes. The distance between the eyes is a sign of identifying male and female flies. Female flies are farther away from their eyes, while male flies are closer to their eyes. There is a pair of short antennae in front of the head, which is the sensitive olfactory organ of flies.

Growth process

Flies are completely metamorphic insects. Their lifetime consists of four stages: eggs, larvae (maggots), pupae and adults. The morphology of each stage is completely different. Females lay their eggs on rotten organisms, such as carrion or feces, which the larvae feed on after hatching. Certain species of flies are oviparous, such as hemp flies.


The egg is white, banana-shaped or oval, about 1 mm in length. There are two ridges on the back of the eggshell. The membranes between the ridges are the thinnest. The larvae emerge from the ridges when they hatch. The development time of eggs is 8-24 hours, which is related to environmental temperature and humidity. The eggs do not develop below 13 C and die below 8 C or above 42 C. In the following range, the incubation time of eggs decreases with the increase of temperature: 20 hours at 22 C; 16-18 hours at 25 14 hours at 28 C; 8-10 hours at 35 C. The relative humidity of growth matrix also affected the hatchability of eggs: when the relative humidity was 75-80%, the hatchability was the highest; when the relative humidity was lower than 65% or higher than 85%, the hatchability decreased significantly.


The larvae, commonly known as maggots, have three instars: the first instar larvae are 1-3 mm in length and have only posterior valves. After molting, it becomes 2-year-old, 3-5 mm long, with front valves and back valves split. The second ecdysis is 3 years old, 5-13 mm long and 3-cleft posterior valves. The body color of maggots changes from transparent, milky white to milky yellow in the first to third instars until they mature and pupate. The 3rd instar larvae are long conical with thin front ends and truncated back ends without eyes or feet. The life characteristics of maggots are that they like to drill holes, fear strong light, and live in the dark and shelter of breeding all day long. It has a variety of edible, corrupt fermentation organic matter, are its delicacies. Larvae stage is the key period of fly life. Its growth and development are directly related to the individual size and reproductive efficiency of fly species. Larvae’s skull and pharynx, posterior valvular slice, posterior valvular fissure and terminal abdominal process are commonly used for classification and identification. The third instar larvae have small head, claw-like mouth and asymmetrical left and right sides.


The pupa is the third metamorphosis in the life history of flies. It is barrel-shaped or peripupae. Its body color changed from light to dark, and eventually to chestnut brown, 5-8 mm long. The pupa shell undergoes constant metamorphosis, and once the embryonic form of flies is formed, it enters the stage of emergence. During emergence, flies alternately expand and contract the frontal sac of the head, squeeze the end of the pupa shell and crawl out, and reach the surface through loose sandy soil or other culture materials. From pupation to eclosion, it is called pupal stage.


The body length is 5-8 mm, grayish brown, compound eyes glabrous, dark red, and the frontal width of male flies is 1/4-2/5 of the eye width; the frontal width of female flies is almost equal to the width of one side of the compound eye. Antennae grey-black, short flat, short antennae awns, base thick, back and abdomen with feathers on both sides, until the tip of the awn, the next whisker brown-black. Appearance of mouth organ suction type, can see a thick and short beak, consisting of three parts, the base beak is inverted cone, the middle beak is short and thick as a cylinder, the end beak developed into two flaps, that is, called lip flaps; beak can be freely retracted. There were four black longitudinal stripes in the middle thoracic shield, cilia in the central depression of the anterior thoracic side plate, no clusters of anterior and posterior rigid hairs in the upper rib of the axillary valve, and hairs in the lower side of the posterior valve. The wing is transparent, the vein is brown and yellow, the base of the front vein is yellow and white, and the end of the fourth longitudinal vein bends sharply forward into a fold angle, and the end of the fourth longitudinal vein is close to the end of the third longitudinal vein. The feet are black, with a gray-yellow pink quilt, and the abdomen is oval and yellow, especially on both sides of the base. There are broad black longitudinal strips in the center of the abdomen and cilia on the first web of the abdomen. Flies have six legs (three pairs). The front pair corresponds to the forelimbs of human, kangaroo, monkey, panda and other mammals. The back pair is the supporting and energetic thighs, which corresponds to the hind limbs of human, kangaroo, monkey, panda and other mammals.

When the 3rd instar fly matures, it tends to pupate in a slightly low temperature environment. However, pupae stopped growing when the temperature was lower than 12 and died when the temperature was higher than 45. Within the suitable range, the pupal period was shortened with the increase of temperature. It takes 17 to 19 days at 16 20 10 to 11 days; 6 to 7 days at 25 4 to 5 days at 30 and 3 to 4 days at 35 which is the best development temperature. The pupae is characterized by relatively cold tolerance. According to the experiment, the pupae of Musca domestica returned to normal room temperature after 4 days’refrigeration in a refrigerator with temperature of 1 C and ambient humidity of 85%. The emergence period was only one day later than that of normal pupae period. The emergence rate would not be reduced after 3 days’ refrigeration in the above environment.

Environmental requirements for maggots

Humidity: The optimum ambient humidity for 1-2 instars is 61-80%, and the optimum humidity is 71-80%. The optimum environmental humidity for the third instar maggots is 61-70%, and over 80% of them can not develop normally. It can be seen that the development of maggots requires a certain humidity, but not the higher the better. In production practice, the appropriate humidity is 65-70%, less than 40%, the development of maggots is stagnant, pupation is rare, and even lead to maggots death.

Food: One of the important ecologies of maggots is omnivorous, and feeds locally in their habitats. Some people have found 764,400 maggots and pupae in 1.5-inch pig manure. Animal feeds, plant feeds and proteins in microorganisms are all nutrients that fly maggots like to ingest. The quantity, quality, fermentation temperature and water content of food are directly related to the development effect of maggots. The third instar larvae stop feeding when they mature. They often leave breeding sites and pupate in the loose soil near them under the conditions of low temperature 15-20 C and low humidity. Tens of thousands of pupae of houseflies have been found in cracks in the cement floor of the roots of the inner walls of a distillery.

Ventilation: Air circulation is conducive to the growth and development of maggots. In garbage dumps, maggots often distribute in the corners and roots of walls with large voids. To grasp the growth characteristics of the fly maggots mentioned above, and to guide the production practice, is of great benefit to improve the efficiency of fly maggots breeding.

Environmental requirements for pupae stage

Humidity: According to the experiment, the optimum medium humidity for pupa development is 45-55%, higher than 70% or lower than 15%, which will obviously affect pupa emergence. If the pupa is immersed in water, the longer the time, the lower the pupation rate of maggot and the lower the emergence rate of pupae. Some people have fished 1000 pupae from liquid waste and turned them into dry environment. One pupae failed to emerge into adult flies. It is worth mentioning that if the nutrients of fly maggots are insufficient and the pupae of fly maggots are barely strengthened without full development, the pupae can also hatch into flies, but more than 95% of the adult flies are males. They only eat food and do not lay eggs, and all of them die within 10 days or so. Therefore, to keep pupation maggots, we must use sufficient nutrients to make them fat and fat, the larger the proportion of females. Only when more females breed flies can the spawning amount be guaranteed and the yield be stable.

Adult flies: Adult flies emerged from pupae need to undergo several stages of “static-creeping-extending-wing-body wall hardening” to develop into adult flies with flying, feeding and reproductive abilities. Musca domestica emerged from pupae with soft, grayish body wall, undeveloped wings and no retraction of frontal sac. Later, the wings extend, the epidermis hardens and the color deepens. After 1-1.5 hours, the wings can fly. The adult flies began to move and feed 2 to 24 hours after emergence at 27 C.

Ecological habits


Flies have the physiological characteristics that one mating can lay eggs for life. A female fly can lay eggs for 5-6 years in a lifetime.

The number of eggs laid per time ranged from 100 to 150, with a maximum of about 300 eggs. It can reproduce 10 to 12 generations in one year. At suitable temperature, male housefly can mature and mate 18-24 hours after emergence and female housefly 30 hours after emergence. The mating time is usually from 5:00 to 7:00 in the morning. Sensitive sense of smell, sex hormones and vision are all important factors to promote mating between male and female flies. A pair of mating flies can stay in one place for a long time, crawl together, fly together, and mate effectively for up to 1 hour. Most houseflies mate only once in their lifetime. The semen of male flies can be stored in the fertilizer sac of female flies for a long time, stimulating oviposition and continuously fertilizing the eggs for 2 to 3 weeks without mating with another male fly. This is rare in other insects. This is an important reason for the high fecundity of flies.

Lay eggs

The peak period of spawning is from 17:00 to 19:00 every day. The length of the pre-oviposition period (i.e. the time from emergence to the first oviposition) of female flies is closely related to the environmental temperature: the average time is 9 days at 15 C, only 1.8 days at 35 C, and no oviposition occurs below 15 C. After mating, female flies often crawl into breeding crevices, such as human and animal feces, and extend oviposition tubes to lay eggs in the depth of breeding, so as to facilitate the full protection of eggs. Flies have amazing fecundity. According to observation, about 100 eggs are laid in each batch of houseflies in the laboratory. One female fly can lay 10-20 batches of eggs throughout her life, and the total number of eggs is 600-1000. In nature, each female fly can lay 4 to 6 batches of eggs in a lifetime, with intervals of 3 to 4 days. The number of eggs laid per batch is about 100, and the total number of eggs produced is 400 to 600. Even in North China, houseflies can reproduce 10 to 12 generations a year. According to the most conservative estimates, each female fly can produce 200 offspring, then 100 females only need 10 generations, and the total number of flies will reach 2 trillion!

Feeding habits

The food of flies depends on their species. There are those who specialize in sucking nectar and plant juice, those who specialize in cannibalism, animal blood or animal wound blood and eye and nose secretions. The common houseflies, golden flies, Lucilia sericata, Lily flies and hemp flies belong to omnivorous flies, that is, they widely eat human food, animal secretions and excreta, kitchen waste and organic matter in garbage, etc. They have a strong tendency for sugar, vinegar, ammonia and fishy taste. According to research, female flies can not develop and lay eggs if they only supply water, sugar and carbohydrates, but only when they are fed with protein or amino acids, can they lay eggs normally. Female houseflies fed with royal jelly can shorten the prophase of oviposition and increase the amount of oviposition.

The food of flies is very mixed. They like fragrance, sweetness, sour and stink. When they take food, they spit out their pouch fluid to dissolve the food. Their habit is to eat, spit and pull at the same time. Some people have observed that flies defecate 4 to 5 times a minute when food is abundant.

Flies also eat bacteria that are harmful to themselves, so the method of “vomiting while eating” helps to eliminate bacteria quickly. It takes only 7 to 11 seconds for flies to feed, absorb nutrients and discharge waste. When encountering bacteria with rapid reproduction ability, the fly’s immune system will emit BF64 and BD2 globulins. Once contacted with bacteria, it will “explode” and “die with bacteria”. The two globulins are always emitted in pairs and never in disorder.

It is worth pointing out that the bactericidal ability of BF64 and BD2 is thousands of times stronger than that of penicillin. If BF64 and BD2 can be extracted from flies for human treatment, it will bring good news to human beings.


Temperature, humidity, food and water are the factors affecting the life span of flies. The optimum temperature is 25-33 C and 60-70% air humidity. Female flies live longer than male flies, with a life span of 30 to 60 days and 112 days under laboratory conditions. Flies can live for half a year in cold wintering conditions.

The life span of a fly can last about one month in midsummer. However, in the case of low temperature, its life can be prolonged by 2 to 3 months, and it can hardly carry out activities when the temperature is lower than 10 C, and its life is longer. The adult life span of a common fly is 15-25 days. If its larval and pupal stages are included, its life span is 25-70 days.

Activity characteristics

Flies are insects that move frequently in the daytime and have obvious phototaxis. At night it rests still. Activities and habitats depend on fly species, season, temperature and region. In some seasons, stall rot flies, summer side flies and city flies also invade houses. Golden Fly, Lucilia sericata, Lily Fly, Vomit Fly, Sarcophilus melanogaster and so on are mainly active and live outdoors.

The activity of flies is greatly affected by temperature. It can only crawl at 4-7 C, fly at 10-15 C, feed, mate and lay eggs at above 20 C. It is especially active at 30-35 C. It ceases to move at 35-40 C because of overheating and kills at 45-47 C. Flies are good at flying. The flying speed can reach 6-8 km per hour, and the highest flying speed is 8-18 km per day and night. Usually, however, most of the activities are within the radius of 100-200 m, mostly no more than 1-2 km.

Flying characteristics during takeoff: Flies always bounce off the ground and spread their wings in 0.03 seconds through the “pedal” action of the middle and hind feet during the start-up stage of takeoff. The fly’s flight path and ground angle are often less than 40 degrees, and only in very occasional cases can it appear a nearly vertical take-off dip, but after 10 mm from the ground it will turn to a tilt angle.

The way flies overwinter is quite complicated. It can overwinter as pupa, as well as by maggots and adults. In the northern frigid and temperate regions, there are no active flies in nature, but there are still adult flies in the artificial heating room. Vegetable greenhouse often becomes the birthplace of large numbers of flies when the next spring is warm. In the south of the Yangtze River and some parts of North China, the average temperature in winter is below 0 C. Flies can skillfully overwinter as pupae. In a few areas, dormant females and maggots covered with livestock and poultry dung can also be found. In the subtropical region of South China, the average temperature is above 5 C, and flies do not have dormancy, so they can continue to breed and reproduce.

Ecological Importance

Flies feed mostly on decaying organic matter, so they are common in poor hygienic environments. Flies have sucking mouthparts that can contaminate food and spread diseases such as dysentery. In clinical medicine, live maggots can be inoculated into wounds to sterilize and debride wounds.

Protein-rich maggots are important baits and feedstuffs, which can be manufactured in factories because their crude protein content is over 60%, and their protein content is higher than that of fish meal which is widely used by human beings.


Housefly: small and medium-sized species, body length 5 ~ 8mm, whole body dark gray, male two compound eye spacing is very narrow, female two compound eye spacing is wider. There are 4 black vertical stripes on the chest and back, the base of the abdomen is brownish black at the base, the end is orange, and there is a wide black vertical line in the middle of the back. It is the most important fly species in urban residential areas in China, and it is also the most important fly species entering the indoors.

Gold flies: large and obese, body length 7 ~ 11mm, the body has a blue-green metallic luster, male head two eyes are huge, bright red, 1/3 small eye under the compound eye is smaller, upper 23 small eye surface Large, curved, distinctly demarcated, the distance between the two compound eyes is very narrow; the distance between the female and the compound eyes is very wide, the cheeks of the two sexes are orange, the lower jaw is brown, the hair is fine, and the back of the abdominal base is black. Sexual living area fly species.

Green fly: medium to small, body length 5 ~ 8 mm, body color is bronze or turquoise, male narrow, wide female, abdomen in addition to the base back sheet brown black, the rest of the back sheet no black cross strap, It is a typical outdoor living area fly species that can invade indoors.

Hemp flies: medium to large species, up to 13mm long, suitable for outdoor habitats. The flies do not narrowly divide the male and female by eye spacing, but to observe the tail, the male tail has a bright black or red spherical bulging end, the female has no, but the body is more obese, the two sides have three black vertical stripes on the back, and the back of the abdomen has black and white. The checkerboard pattern of the phase can be discolored according to the refraction of the light. Generally, it is large in size and small in size.

City fly: body length 4 ~ 7mm, slightly smaller than the housefly. The body color is light gray. Also, the distance between the compound eyes is divided into male and female, female wide and male narrow. There are two black vertical stripes on the back of the chest; the female divides a pair of small forks in front of the shield ditch, only half of the main fork. The male black vertical stripes are not bifurcated, the abdomen is dark brown, and there are black vertical stripes in the middle of the back of the abdomen. There are small silver-gray spots on both sides, which are longitudinally distributed.

Habits and characteristics

From their individual perspective: the smaller individuals in the group are generally male, and the larger ones are generally female;

Look at their stomachs: the flies of male flies are small and flat, and the belly of female flies is large and round;

Look at their ass: the buttocks of the male flies are round, and the ass of the female flies are pointed.

Food preference and foraging methods

Fly is an omnivorous insect, and common species prefer sweets or rot, such as: squid and parasitic flies prefer to visit flowers; fruit flies and fruit flies prefer to eat fruit or fruit; flies, house flies and flies Peat and feces are preferred.

The large, elephant-like sucking mouthparts are the tools used by most flies to feed liquid food. Before foraging, many flies will secrete digestive juice, dissolve the nutrients in the food, and then eat and absorb.

Habitat environment

The habitat (habitat) of the fly is closely related to its food preferences.The squid flies often hover around the flowers, while the carnivorous meat, the feces are flies and flies are frequent visitors to landfills.Because house flies, fly, flies and other flies often feed between human food and dirt, they become the culprit for spreading bacteria and epidemic sources.

Larval habit

The larvae of the scorpion flies specifically prey on locusts or scale insects that are harmful to plant health and contribute greatly to the suppression of pests. The parasitic fly larvae will be parasitic in the body of butterflies and moth larvae. After maturity, they will be drilled out of the main body, causing the host to die, which invisibly reduces the chance of crop damage. The female flies of the fruit flies often lay eggs on the fruit of the orchard or farmland so that the larvae can grow on the fruit, but they also lose the edible value of these fruits, causing economically serious losses.

However, not all of these different flies are harmful to humans, and some species have direct or indirect contributions to humans.

Growing environment

The optimum temperature for flies is 27 to 30 °C. Flies can move at 8~12°C, but they can’t mate, they can’t stand on food, they can only fall on the ceiling and the wall, they don’t like to move. When they are minus 5°C, they die 3 to 5 days. The larvae require higher temperature than adult worms, and the most suitable temperature for development is 35 °C. It stops at 1-2 °C and dies at minus 5-6 °C. When the temperature is too high 45-55 °C, its growth rate is faster than normal temperature. Reduce it by half. The fly larva requires a food temperature of 30 to 35 ° C. In terms of humidity, adults require indoor humidity of 55 to 60%. When the humidity is too high, the fly legs and body are prone to moisture and hinder the activity. The humidity required for larval growth is 65 to 70%. Flies like to move in bright places, the greater the brightness, the greater the amount of activity. Artificially raised flies should have lighting fixtures in the room and be illuminated for more than 10 hours a day.


The flies are harmful to humans by carrying a variety of pathogenic microorganisms. The flies have many hairs on the surface, and the foot grips can secrete mucus. They like to crawl and eat in the excrement, sputum, vomit and body of human or animal, which is easy to adhere. A large number of pathogens, such as Vibrio cholerae, Salmonella typhi, Shigella, Hepatitis, polio, hepatitis A and hepatitis A, etc And the habit of brushing, the pathogen attached to it quickly contaminates food and tableware. When flies eat, first spit out the sac fluid, dissolve the food before inhaling, and eat, spit, and pull; this will spit out the pathogens that were originally eaten into the digestive juice, pollute the food it has eaten. People who go to eat these foods and use contaminated tableware will get sick. The prevalence of cholera, dysentery and bacterial food poisoning are directly related to the spread of flies, but it is not useless. Without it, humans will be trapped in rancid places.


With the development of animal husbandry in China, the intensive livestock and poultry farms are increasing. Some farms are not paying attention to the harmless treatment of livestock and poultry excrement, and they are closer to the residential areas, which makes the pollution level of the surrounding environment. Increasingly serious, leading to the breeding of harmful organisms, such as the harm of flies has become a very serious problem.