Unraveling the Life Cycle of a House Fly: A Comprehensive Guide

Introduction

The house fly, scientifically known as Musca domestica Linnaeus, is a globally recognized pest found in close proximity to human activities and habitations. As a cosmopolitan species, it thrives in diverse environments, from farms to homes, making it a common nuisance worldwide. House flies are prevalent in areas associated with livestock, such as hog and poultry farms, horse stables, and ranches. Beyond being a mere annoyance, house flies are significant vectors of disease, capable of transporting numerous pathogens. High populations of these flies can pose not only an inconvenience to agricultural workers but also a considerable public health risk, especially in areas near human settlements.

Figure 1. Adult house fly, Musca domestica Linnaeus. Image courtesy of Jim Kalisch, University of Nebraska-Lincoln.

Global Distribution

Originating from the steppes of central Asia, the house fly has expanded its habitat to encompass all inhabited continents. Its adaptability allows it to flourish in climates ranging from tropical to temperate zones, and in environments from rural to highly urbanized settings. While commonly linked to animal waste, the house fly’s ability to feed on garbage has facilitated its proliferation in virtually any location inhabited by humans.

Detailed Life Cycle and Description

The house fly undergoes complete metamorphosis, a biological process characterized by distinct developmental stages: egg, larva (maggot), pupa, and adult. In colder climates, house flies typically overwinter in the larval or pupal stages, seeking shelter in manure piles or other protected areas. Optimal conditions for their development are generally found during warm summer months, enabling them to complete their life cycle in as short as seven to ten days. However, less favorable conditions can extend this period to as long as two months. In temperate regions, house flies can produce between 10 to 12 generations annually, while subtropical and tropical areas may see more than 20 generations per year.

Figure 2. The life cycle of a house fly, Musca domestica Linnaeus, illustrating the progression from eggs to larva, pupa, and finally, the adult stage. Image courtesy of Jim Kalisch, University of Nebraska-Lincoln.

Egg Stage

The house fly egg is white, approximately 1.2 mm in length, and while laid individually, they are often found clustered in small groups. A single female can lay up to 500 eggs over a period of three to four days, in batches of 75 to 150 eggs. The number of eggs laid is directly influenced by the size of the female, which is primarily determined by larval nutrition. Egg production peaks at temperatures between 25 to 30°C. Multiple females often deposit eggs in close proximity, leading to large aggregations of larvae and pupae. Moisture is crucial for egg survival, as they will not hatch if they dry out.

Figure 3. An adult house fly alongside its eggs, Musca domestica Linnaeus. Image courtesy of Jerry F. Butler, University of Florida.

Larval Stage

Upon hatching, usually within eight to 20 hours in warm conditions, the legless maggot, or larva, emerges. Early instar larvae are creamy white, cylindrical, and taper towards the head, measuring 3 to 9 mm in length. They possess dark hooks in their head region and posterior spiracles with sinuous slits surrounded by a black oval border. These maggots immediately begin feeding on the material where the eggs were laid.

Larvae undergo three instars, growing to 7 to 12 mm in length when fully developed, exhibiting a greasy, cream-colored appearance. High moisture content in manure is conducive to larval survival. The optimal temperature for larval development is between 35 to 38°C, although survival is broader, ranging from 17 to 32°C. Larval development is typically completed in four to 13 days under optimal temperatures but can extend to 14 to 30 days at 12 to 17°C.

Nutrient-rich substrates, such as animal manure, are ideal for larval development. Surprisingly, only small amounts of manure are needed, and even soil or sand with traces of degraded manure can support successful underground development. Once fully grown, the maggot may travel up to 50 feet to find a dry, cool location near breeding material for pupation.

Pupal Stage

The pupa, about 8 mm long, develops inside a pupal case formed from the last larval skin. The color of this case changes with age, from yellow to red, brown, and finally black. The pupal shape is distinct from the larval form, being bluntly rounded at both ends. Pupal development takes two to six days at 32 to 37°C, but extends to 17 to 27 days at around 14°C. The adult fly emerges by using a pulsating sac on its head, the ptilinum, to break through the pupal case.

Figure 4. A prepupa and a sequence of puparia showing color changes with age in Musca domestica Linnaeus. Image courtesy of Jim Kalisch, University of Nebraska-Lincoln.

Adult Stage

The adult house fly measures 6 to 7 mm in length, with females typically larger than males. Females can be distinguished by a wider space between their eyes compared to males, where the eyes are almost touching. Adult flies have reddish eyes and sponging mouthparts. Their thorax features four narrow black stripes, and a characteristic sharp upward bend is noticeable in the fourth longitudinal wing vein. The abdomen is gray to yellowish with a dark midline and irregular dark markings on the sides, while the underside of the male is yellowish.

Figure 5. A detailed view of an adult house fly, Musca domestica Linnaeus. Image courtesy of Matt Aubuchon, University of Florida.

Figure 6. A lateral view of the head of an adult house fly, Musca domestica Linnaeus, highlighting its features. Image courtesy of Matt Aubuchon, University of Florida.

House flies are often mistaken for stable flies (Stomoxys calcitrans) and false stable flies (Muscina stabulans), all belonging to the same family.

Figure 7. Dorsal comparison between an adult stable fly, Stomoxys calcitrans (left), and a house fly, Musca domestica (right). Image courtesy of Jim Kalisch, University of Nebraska-Lincoln.

Figure 8. Ventral comparison between an adult stable fly, Stomoxys calcitrans (left), and a house fly, Musca domestica (right). Image courtesy of Jim Kalisch, University of Nebraska-Lincoln.

Adult house flies typically live for 15 to 25 days, but their lifespan can extend up to two months, influenced by food availability, especially sugar, and cooler temperatures. They cannot survive more than two to three days without food. Food is essential for copulation, which can last from two to fifteen minutes. Oviposition begins four to 20 days post-copulation. Females require protein-rich food for egg production, which manure alone does not provide. The reproductive potential of house flies is immense; theoretically, a single pair could generate trillions of offspring within months under ideal conditions, though this potential is never fully realized in nature.

Flies are diurnal, inactive at night, resting on ceilings, beams, wires inside buildings, trees, shrubs, and outdoor wires and grasses. In poultry farms, nighttime aggregations are commonly found on branches and shrubs outdoors, while indoors, they gather in ceiling areas of poultry houses.

Breeding site preferences vary, but studies indicate horse manure, human excrement, cow manure, fermenting vegetable matter, and kitchen waste are highly suitable. Swine facilities are noted to have the highest fly abundance, while poultry facilities the least. Fruit and vegetable waste piles, partially incinerated garbage, and incompletely composted manure are also prime breeding grounds.

Damage and Medical Significance

House flies are notorious for breeding in poultry manure in caged hen houses, leading to severe infestation issues. Although they do not bite, controlling Musca domestica is crucial for human health and comfort due to their role in disease transmission. The primary harm they cause is annoyance and the indirect damage from pathogen transmission. They can carry viruses, bacteria, fungi, protozoa, and nematodes, acquired from garbage, sewage, and filth, and transmit them to food through their mouthparts, vomit, feces, and body contact.

The transfer of pathogens from feces to uncooked human food is particularly concerning. Pathogens can survive in flies’ bodies for days, being transmitted through defecation or regurgitation. In areas lacking proper sanitation, such as those with open latrines, the risk of health problems escalates, especially near food markets, hospitals, or slaughterhouses. Common pathogens transmitted by house flies include Salmonella, Shigella, Campylobacter, Escherichia, Enterococcus, Chlamydia, and many others causing diseases like diarrhea, shigellosis, food poisoning, typhoid fever, dysentery, tuberculosis, anthrax, ophthalmia, and parasitic worm infections.

Economic Threshold

The economic threshold for house fly control varies depending on the setting. In homes, even a few flies may warrant control measures. At waste management sites, the threshold for complaints might be around 150 flies per flypaper in 30 minutes.

Monitoring fly populations involves using baited traps, sticky ribbons, or spot cards in livestock facilities. Spot cards, typically 3×5 inch white index cards, are placed on fly resting surfaces for seven days. Over 100 fecal or vomit spots per card per week indicates a significant fly problem requiring intervention.

Tolerance levels are highly context-dependent. In sensitive environments like food processing plants, restaurants, and hospitals, even minimal fly presence is unacceptable. However, in livestock or poultry production, some fly presence is often unavoidable. Conflicts arise when residential areas develop near agricultural facilities, as residents are less tolerant of the resulting fly populations.

Management Strategies

Common house fly control methods include sanitation, trapping, and insecticide use. Integrated fly control programs and biological control methods are also increasingly utilized.

Sanitation and Cultural Control

Sanitation is fundamental to fly management. Eliminating breeding materials, such as food waste and manure, or isolating them from adult flies is crucial. Given the house fly’s rapid life cycle, removing wet manure at least twice weekly is necessary to disrupt breeding. Straw, an excellent breeding material, should be avoided as bedding, and spilled feed should be cleaned up promptly. Municipal-level fly control within a 1 to 2 km radius can effectively prevent infestations.

Garbage management is key; cans and dumpsters should have tight lids and be cleaned regularly. Dry waste should be bagged and sealed. Waste receptacles should be located away from building entrances. For waste disposal sites, refuse should be mixed with inorganic waste or covered with a 15 cm layer of inorganic waste to reduce breeding potential.

Around homes and businesses, screens on windows and doors, air doors, and covered trash containers are effective barriers. Bagging household trash and burying it under at least 15 cm of soil in landfills also aids in control. In agricultural settings, manure can be spread thinly to dry quickly, becoming unsuitable for breeding. Composting manure, if properly turned, can also be effective. Liquefying and storing manure anaerobically in lagoons is another option, though solids separation is eventually necessary.

Trapping Methods

Fly traps can be effective when used in sufficient numbers and placed strategically, both indoors and outdoors. House flies are attracted to white surfaces and odorous baits. Indoor traps include ultraviolet light traps, which either collect flies or electrocute them. One trap per 30 feet of wall is recommended indoors, away from food preparation areas. Outdoor placement should target building entrances, alleyways, trees, animal resting areas, and manure piles. Building openings should be well-screened to prevent fly entry.

Baits like molasses, sugar, fruit, or meat enhance trap effectiveness. Muscalure, a sex and aggregation pheromone, is also used in commercial baits for population suppression and monitoring. Ultraviolet light traps are useful for population assessment and non-chemical control indoors in agricultural and non-agricultural settings. They are most effective near entryways and at lower heights, operating continuously, especially when room lights are off.

Biological Control

Increasing insecticide resistance and environmental concerns have driven interest in biological control. Natural suppression occurs through chalcidoid wasps, such as Muscidifurax and Sphalangia species. Other parasitoids and predators like histerid and staphylinid beetles also contribute, but house flies can still proliferate rapidly under ideal breeding conditions. Key wasp species in poultry facilities include Muscidifurax raptor and Sphalangia cameroni. Leaving a layer of old manure can support these beneficial insects.

Figure 9. House fly puparia, each showing emergence holes of parasitic wasps that developed by feeding on the fly pupae. Image courtesy of USDA.

Figure 10. A Muscidifurax raptor wasp on a house fly puparium, demonstrating its parasitic behavior. Image courtesy of USDA.

Augmentative biological control involves releasing insectary-reared parasitoids like Muscidifurax raptor, Muscidifurax raptorellus, Sphalangia endius, and Sphalangia nigroaenea. These species are suited to different conditions and pupation depths. Muscidifurax raptor is effective against flies pupating near the manure surface, while Sphalangia cameroni is better for deeper pupation. Sphalangia endius has shown success parasitizing pupae both above and below the soil surface. Black dump fly larvae (Hydrotaea aenescens) are also used as predators of house fly larvae in poultry farms as a pesticide-free method.

Integrated Fly Control

Integrated fly control in poultry houses includes selective insecticide applications against adults, starting early in spring and continuing through warm months, while leaving manure undisturbed during fly breeding seasons. Manure removal is done once early in spring before fly emergence.

Chemical Control

In commercial egg production, chemical control involves adulticides or larvicides to reduce adult fly populations. Residual wall sprays are applied to fly congregation areas. Rotating insecticide formulations with different modes of action is crucial to manage insecticide resistance. Outdoor chemical control includes boric acid in dumpsters, treating walls near breeding sites with microencapsulated or wettable powder formulations, and using fly baits near adult feeding sources.

Manure treatment with insecticides is discouraged due to its negative impact on biological control. Insect growth regulators fed to livestock can inhibit fly breeding in manure. Insecticides are also applied to adult resting places or used in bait stations. However, continuous insecticide use has led to widespread resistance. Indoor chemical controls include automatic misters, fly paper, electrocuting traps, and baited traps in low-fly-density areas.

Selected References

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Authors: Hussein Sanchez-Arroyo and John L. Capinera, University of Florida
Photographs: Jerry F. Butler and Matt Aubuchon, University of Florida; Jim Kalisch, University of Nebraska – Lincoln; USDA
Web Design: Kay Weigel
Publication Number: EENY-48
Publication Date: August 1998. Latest revision: April 2017. Reviewed: June 2020.
Copyright University of Florida ~ An Equal Opportunity Institution
Featured Creatures Editor and Coordinator: Dr. Elena Rhodes, University of Florida