Common fly species

Flies are insects in the order Diptera, characterised by having a single pair of wings used for flight. Common species found around facilities include house flies, blow flies, drain flies, phorid flies and fruit flies. Each species has different characteristics, breeding sources and levels of risk.

What are flies and what are their identifying characteristics?

Flies are a common name for many groups of insects belonging to the order Diptera. “Di” means two, while “ptera” refers to wings. One of the most distinctive characteristics of this group is that they have only one main pair of wings used for flight.

The hind wings have evolved into a pair of small structures called halteres. In simple terms, these organs help flies maintain balance and control their movement during flight. This characteristic helps distinguish flies from many insect groups that have two pairs of wings.

The body of an adult fly consists of three main sections: the head, thorax and abdomen. The head usually has large compound eyes. Mouthpart structure, body colour, size, wing shape and activity patterns vary between species.

Fly species should not be identified solely by size or colour. Some species are very small and are often grouped together as “drain flies”, even though the actual source may involve fruit flies or phorid flies.

What attracts flies?

Food sources and breeding sites vary by species. Decaying organic matter, food, wastewater, animal faeces, ripe fruit, sugary beverages and animal carcasses may all be associated with the activity of certain fly groups.

In factory and manufacturing facility environments, areas requiring attention usually include garbage storage, raw material receiving zones, washing areas, floor drains, dining areas, loading docks, and facility perimeters. An important point is that where flies are seen is not necessarily where they are breeding. For production facilities, identifying these locations should be part of the fly control procedure in factories categorized by risk area.

For example, adult flies may be detected in a packaging area while the source is located in an external waste room. Drain flies may appear on restroom walls while their larvae are developing deeper within the organic film inside a drainage line.

Therefore, merely spraying where flies are seen may reduce the number of adult individuals in the short term, but it does not resolve the underlying breeding source.

Why is correct fly identification important?

Correct species identification helps narrow the scope of investigation. When drain flies are found, drainage systems and moist organic films should be prioritised for inspection. If blow flies suddenly appear in unusually large numbers, investigating decaying organic matter or an animal carcass may be more important than adding more insect light traps.

House flies present a different situation. Waste rooms, refuse storage areas, receiving zones, animal faeces or spilled organic materials may support their life cycle. Identification is therefore not simply about naming the insect. It provides the input data needed to determine the breeding source, entry routes and areas requiring action.

Which common fly species are found around facilities?

Not all fly species behave in the same way. Several species may occur within the same facility, particularly where different environmental conditions exist across production areas, warehouses, waste rooms, drainage systems and outdoor areas.

What are the characteristics of house flies?

House flies have the scientific name Musca domestica. This is one of the fly species closely associated with human activity environments. Adult flies are usually grey in colour. Their thorax has dark longitudinal stripes that are relatively easy to observe up close. This insect species can appear around food, waste areas, animal faeces, and various forms of decaying organic matter.

In factories and manufacturing facilities, house flies are commonly recorded around entrances, waste rooms, receiving areas, canteens and areas containing organic material. A high number of house flies indoors should not simply be addressed by increasing the amount of insecticide applied. External sources, sanitation conditions, frequently opened doors and potential entry points should also be inspected.

Musca domestica

What are the characteristics of blow flies?

Blow flies belong to the family Calliphoridae. One of their most recognisable characteristics is a metallic blue, green or iridescent body. These flies are generally relatively large and more noticeable than small flies found around drains or food.

When a large number of blow flies suddenly appear in the same area, this may indicate that a source of decaying organic matter requires investigation. Waste rooms, rubbish bins, food waste, dead birds, rodents or other animals in concealed locations should all be considered depending on site conditions.

A common situation that can cause confusion is when blow flies appear inside a building but no source is found within the production area. In such cases, roof spaces, utility voids, suspended ceilings and external areas may need to be inspected. The presence of blow flies does not automatically prove that a facility has a serious sanitation problem. Conclusions should only be made after the source and site conditions have been investigated.

Blow flies (Calliphoridae)

What are the characteristics of drain flies?

Drain flies are usually small. Their bodies and wings are covered with fine hairs, giving them a moth-like appearance when they rest on walls. These insects are commonly found around floor drains, sinks, restrooms, washing areas or other locations with high moisture levels. The most important area to investigate is often beneath the location where the adult flies are seen.

In some drainage systems, organic material can accumulate along internal surfaces and form a moist film. This environment may provide both food and a development site for drain fly larvae. Therefore, spraying adult flies or wall surfaces may reduce the number of visible flies but does not necessarily eliminate the breeding site.

When drain flies continuously appear, it is necessary to check drainage conditions, accumulated organic film, hard-to-clean areas, and pipe sections with suitable conditions for larvae development. If the issue is concentrated around restrooms, floor drains, or pipes, you can see more about how to deal with drain flies and larvae in drainage systems.

Drain fly

How are phorid flies different from drain flies?

Phorid flies belong to the family Phoridae. They are usually small and are easily confused with other small fly species. One notable morphological feature is the arched thorax, which gives them a characteristic “humpbacked” appearance. While drain flies usually have hairy bodies and moth-like wings, phorid flies have a different body shape and may move quickly across surfaces.

This distinction has practical importance. If all small flies are incorrectly identified as drain flies, sanitation efforts may focus only on floor drains while the actual breeding source is located elsewhere in decaying organic material. In persistent cases, specimens should be collected from traps or glue boards and identified before treatment decisions are made.

Phorid fly (Phoridae)

Where are fruit flies commonly found?

Fruit flies are small flies commonly associated with ripe fruit, sugary foods, beverages and fermenting materials. In canteens, restaurants, hotels or food processing areas, fruit flies may occur around beverage counters, waste bins, bottles, fruit and locations where organic residues accumulate.

Because of their small size, fruit flies are sometimes incorrectly identified as drain flies. However, the breeding sources of these two groups may differ considerably. If flies are concentrated around fermenting food or beverages, simply cleaning drains may not resolve the problem. Conversely, flies found primarily around floor drains require a different line of investigation.

Quick distinction: fruit flies are commonly associated with food and fermenting materials, while drain flies are more often associated with moist environments and organic films within drainage systems.

Fruit flies

What is the life cycle of a fly?

Most fly species undergo complete metamorphosis, consisting of four stages: egg, larva, pupa and adult. Understanding this life cycle is important because the flying insects visible inside a facility represent only the adult stage. Eggs, larvae and pupae may be present in an entirely different location.

The fly life cycle

Where does the egg stage occur?

Female flies usually select an environment suitable for larval development when laying eggs. The specific environment varies by species. House flies may use decaying organic matter. Blow flies are commonly associated with organic material of animal origin. Fruit flies are linked to fermenting plant material or liquids.

Because of these differences, finding eggs or larvae at the source provides valuable information for identifying the cause of the problem.

How do fly larvae develop?

After the eggs hatch, flies enter the larval stage. Fly larvae are commonly known as maggots. This is a period of intensive feeding and development. Larvae do not resemble adult flies and usually live within or close to their food source.

From a pest control perspective, this stage helps explain why treating adult flies does not necessarily solve the problem. If the breeding area still contains organic matter and provides suitable conditions for larvae development, a new generation of flies can continue to emerge. This is also why a treatment program can fail if the breeding source and environmental conditions have not been eliminated.

What role does the pupal stage play in the fly life cycle?

After the larval stage, the insect enters the pupal stage. During this period, the body undergoes major changes to form the adult fly. Depending on the species and environmental conditions, pupae may remain within or near the material where the larvae previously developed. Adult flies then emerge from the pupae, begin feeding and mating, and start a new cycle.

How long do flies live?

There is no single lifespan that applies to all fly species. Development time from egg to adult and adult longevity depend on the species, temperature, humidity, food availability and other environmental factors.

For this reason, statements such as “all flies take only 3–5 days to reach adulthood” can be misleading unless the species and study conditions are clearly specified. For pest management in factories and manufacturing facilities, more useful information is identifying which life stage is present at the facility and which source is sustaining that life cycle.

For example, a continuous increase in adult fly captures on insect light traps over several monitoring periods may indicate that further investigation is required. The data should be compared with species identification, device location, sanitation conditions and operational changes before conclusions are made.

What risks do flies create for factories and manufacturing facilities?

In factories and manufacturing facilities, flies are more than a nuisance to employees. A greater concern is their ability to move between waste sources and areas where hygiene must be controlled.

House flies, for instance, can come into contact with faeces, waste, and decaying organic matter before moving onto other surfaces. Therefore, the presence of flies in food production areas needs to be recorded and investigated. For F&B facilities, fly control should be included in an overall insect control program for food processing plants, alongside cockroaches, ants, stored product pests, and rodents.

However, the sighting of a single fly should not automatically be interpreted as proof that a product has been contaminated or that a facility will fail an audit. Risk should be assessed based on the species, location, activity level, source and potential for contact with sensitive areas.

How can flies be associated with food contamination?

The main mechanism of concern is movement. A fly may come into contact with an area with poor hygiene conditions and then move to another location. Its legs, body surfaces and mouthparts may contribute to the mechanical transfer of microorganisms from one place to another.

This is why food manufacturing facilities should not focus only on capturing flies. They also need to determine where the flies are coming from. If an insect light trap repeatedly records flies near a production line but the source is not investigated, the trap count only confirms that activity is occurring.

Why is the location where a fly is detected important?

A fly found at the external perimeter and the same species found in a packaging area do not represent the same level of priority. Distance from the product, the openness of the process, type of raw material, frequency of occurrence and the potential for flies to move deeper into the facility all need to be considered. Pest management data should therefore be linked to location, rather than recording only the total number of flies across the entire facility.

For example, if fly captures at a monitoring point increase over several periods, the responsible department can check the surrounding area for changes in sanitation, doors, waste, or environmental conditions. This is also why Dashboards tracking hotspots and pest trends by location are valuable in an IPM program.

Can flies affect audit outcomes?

In facilities operating under food safety management programmes, pest control is commonly part of the preventive system and management documentation. The key point is not to state that “the presence of flies will cause an audit failure”. This would be too absolute and would not accurately reflect the audit process.

Factories need to demonstrate that pest risks are systematically managed: appropriate monitoring equipment is in place, data is recorded, anomalies are investigated, and corrective actions are tracked. This data needs to be compiled into pest control reports to monitor density, trends, and corrective actions.

When an increasing fly trend is identified, the relevant technical questions are: which species is increasing, where is the activity concentrated, where is the suspected source and what changes have resulted from the corrective measures?

Why should facilities not rely only on the number of flies seen?

Visual observation is useful, but it can be influenced by timing and location.

A facility may show no visible fly activity during an inspection while monitoring devices have recorded activity over several days. Conversely, a sudden number of flies near an open door during loading or unloading is not sufficient evidence to conclude that an internal breeding source exists.

Therefore, a good fly management program needs to combine site observation with monitoring equipment data, sanitation conditions, and historical trends. For facilities with multiple areas, numerous organic sources, or persistent fly recurrence, the first step should be assessing risks, identifying breeding sources, and mapping entry points.

For VFC PestMan, PestMan App is used by technicians to record field information, while PestMan Dashboard supports aggregating, tracking, and analyzing management data. Data does not replace technician inspections, but it helps factories and manufacturing facilities gain better visibility into pest activity trends over time.

From this perspective, fly control is not limited to eliminating the insects that are currently flying. Its real value lies in correctly identifying the species, determining the breeding source and monitoring whether corrective actions are bringing pest activity back within an acceptable threshold.

When businesses need to implement these steps into a routine operational program, they can refer to PestMan's insect and rodent control services.

Frequently asked questions about flies

1. What fly species are commonly found around facilities?

Common groups include house flies, blow flies, drain flies, phorid flies and fruit flies. Each group has different morphology and breeding sources, so correct identification is necessary before determining the control approach.

2. What is the difference between house flies and blow flies?

House flies are generally grey with dark stripes on the thorax. Blow flies are usually easier to recognise because of their metallic blue or green bodies and are commonly associated with decaying organic matter.

3. What is the difference between drain flies and fruit flies?

Drain flies usually have hairy bodies and broad wings and are associated with moist environments inside drainage systems. Fruit flies are more commonly found around fruit, beverages, sugary foods or fermenting materials.

4. Why are drain flies commonly found in restrooms?

Drain flies may develop in areas with high moisture and organic material inside drainage systems. If only the adult flies are treated while the larval development source remains, the flies may continue to appear.

5. Why do factories and manufacturing facilities have high fly activity?

Possible causes include organic waste, spilled food, drainage systems, frequently opened doors or breeding sources outside the building. A site inspection is necessary before the specific cause can be determined.

6. Where do flies usually breed?

Different species have different breeding environments. House flies are commonly associated with decaying organic matter, drain flies develop in moist organic environments, while fruit flies are often linked to fermenting materials.

7. Why do flies continue to appear after treatment?

A common reason is that only adult flies have been treated while the areas where eggs or larvae develop remain unchanged. Continued entry from external sources may also cause flies to reappear after treatment.