When a large fly buzzes past, it often sparks curiosity about its identity and why it seems so much bigger than typical houseflies. Many wonder if these are just overgrown versions of familiar insects or entirely different species. Understanding large flies reveals biological distinctions and behaviors that explain their imposing size.
Identifying Common Large Flies
Many large flies are often misidentified, but certain species are common. Crane flies, sometimes called “daddy-long-legs” due to their long, delicate legs, are frequently mistaken for giant mosquitoes. These flies can reach up to 65 mm in length, though most are between 10-25 mm. They are generally brown or grey, have a slender body, and possess a distinct V-shaped suture on their thorax. Despite their mosquito-like appearance, crane flies do not bite humans or animals.
Horse flies are another group of large flies, known for their robust bodies and large, brightly colored eyes. They measure between 6 mm and 32 mm. Their bodies are usually dark brown or black, and some species may have patterned wings. Female horse flies are known for delivering a painful bite, as they require a blood meal to produce eggs. Unlike mosquitoes, horse flies have slicing mouthparts that tear flesh to access blood.
Cluster flies are often observed indoors, especially during autumn and winter. These flies are dark grey, measuring 8 to 10 mm in length, and have numerous golden or yellowish hairs on their thorax. They resemble house flies but are larger, darker, and more sluggish in movement. Cluster flies are nuisance pests that do not bite humans or carry diseases; their larvae are parasitic on earthworms.
Large blow flies, such as bluebottles and greenbottles, are also common. These flies are known for their metallic bluish-green coloration and can be slightly larger than house flies, measuring between 4 and 16 mm long. They are often found near decaying organic matter like garbage or dead animals. While they do not bite humans, blow flies can carry and spread bacteria due to their association with unsanitary materials.
Understanding Fly Size
The size of an adult fly is determined by two factors: its species-specific genetics and the environmental conditions it experiences during its larval, or maggot, stage. For instance, a crane fly is naturally much larger than a common house fly.
Within a species, the availability of food and optimal temperatures during the larval stage influence the adult fly’s final size. Larvae are the primary feeding stage, consuming large amounts of organic matter to grow rapidly. Abundant nutrition allows the larva to accumulate more resources, leading to a larger pupa and, consequently, a larger adult fly. Conversely, limited food or suboptimal temperatures can result in smaller adult flies.
Once a fly emerges from its pupal case as an adult, its size is fixed; it does not grow further. The adult stage is primarily for reproduction and dispersal, with any perceived “growth” being an illusion. This is because insects, including flies, have an exoskeleton that limits their ability to increase in size once they reach their final adult form.
Managing Large Flies
Encountering large flies can be unsettling, but understanding their behavior helps in managing their presence. Many large flies, like crane flies, are harmless and do not bite or pose a health risk. However, some, such as horse flies, deliver painful bites, and others, like blow flies, can carry pathogens due to their association with decaying matter.
For flies that are primarily a nuisance, such as cluster flies, the most effective strategy involves exclusion. Sealing cracks and gaps around windows, doors, and vents can prevent them from entering homes, especially as they seek shelter for overwintering. Removing attractants like decaying organic matter or garbage can also reduce the presence of blow flies.
Basic fly control methods, like using fly swatters or traps, can address individual flies or small infestations. Sticky traps or homemade traps with sweet solutions can be effective for nuisance flies. For persistent or large infestations, professional pest control services might be necessary to identify and treat the source. This often involves sealing entry points or targeted insecticide application in inaccessible areas.