Flies, which belong to the insect order Diptera, are often dismissed as simple household nuisances like the common house fly or the fruit fly. This perception overlooks the fact that the order encompasses over 150,000 described species globally, with the vast majority serving indispensable functions in nearly every ecosystem. These insects are deeply woven into the fabric of nature, performing roles that ensure the stability and continuation of life on Earth.
Essential Decomposers and Scavengers
The most profound contribution flies make to the environment is their role as decomposers and scavengers, ensuring that organic waste is quickly broken down and recycled. Fly larvae, commonly known as maggots, are the primary agents of this process, feeding voraciously on decaying matter such as dead animals, feces, and rotting vegetation. This consumption is a form of bioconversion, where the larvae physically and chemically process the material, making it accessible to other microorganisms like bacteria and fungi.
Blow flies and flesh flies are among the first insects to arrive at a carcass, often within minutes of death, where they deposit eggs that quickly hatch into larvae. These maggots secrete proteolytic enzymes that liquefy the dead tissue, allowing them to absorb the semi-liquid nutrients in a process called extracorporeal digestion. This rapid breakdown prevents the long-term accumulation of waste.
The decomposition process is the engine of nutrient cycling, returning locked-up elements back into the soil for plant use. Specifically, the activity of larvae helps in the recycling of nitrogen, a building block for proteins and nucleic acids, which is released into the soil as frass, or larval excrement. For instance, black soldier fly larvae (Hermetia illucens) are now commercially utilized to efficiently convert biowaste into nutrient-rich residue for fertilizer, demonstrating this natural process on an industrial scale.
Crucial Link in the Food Web
Beyond their role as recyclers, flies represent an enormous food source that connects lower trophic levels to higher ones. All life stages—egg, larva, pupa, and adult—are consumed by a wide range of animals. This abundance transfers energy from decaying matter and plants up to predators.
Many birds, such as swallows and flycatchers, rely heavily on adult flies as a primary source of sustenance during breeding season. Fish, including trout, frequently feed on aquatic fly larvae and emerging adults as a staple part of their diet. The protein-rich maggots also serve as food for small mammals, reptiles, amphibians like frogs, and numerous other invertebrates, including spiders and predatory wasps.
The sheer biomass of flies ensures that energy is effectively moved through the ecosystem. Without this consistent and plentiful food supply, the populations of many insectivorous animals would decline. Flies act as a foundational energy bridge, maintaining the biodiversity and stability of the entire food web.
Unexpected Pollinators
While bees receive most of the attention for their pollination services, many species of flies are significant, though often overlooked, pollinators. Fly pollination is particularly important for certain plants that are not attractive to bees or other insects. Flies often visit flowers to feed on nectar or pollen, inadvertently transferring pollen grains from one bloom to another.
Hoverflies, midges, and bee flies are particularly active pollinators, with their collective numbers in certain environments making them second only to bees in effectiveness. Some plants have evolved specialized mechanisms to attract flies, including emitting odors that mimic carrion or feces to lure species like blow flies, which then carry the pollen.
One of the most notable examples of fly pollination is the cacao tree, Theobroma cacao, the source of chocolate. The tiny, gnat-like biting midges of the genus Forcipomyia are the primary insects responsible for pollinating the cacao flower. These flies are small enough—around one to three millimeters in length—to access the minute, intricate structures of the flower, a task larger insects cannot perform. Without these minute flies, the global supply of chocolate would be threatened.
Practical Uses in Human Science
The predictable life cycle and behavior of certain flies provide valuable tools in applied human sciences, particularly in medicine and forensic investigation.
Forensic Entomology
Forensic entomology, the study of insects in legal contexts, relies heavily on blow flies to help determine the Post Mortem Interval (PMI), or the time elapsed since death. Blow flies are among the first organisms to colonize a body, often laying eggs within minutes to a few hours. By identifying the species of fly and measuring the developmental stage of the oldest larvae, forensic scientists can accurately estimate the minimum time a body has been available for colonization. This estimation is crucial in death investigations.
Maggot Debridement Therapy
In medicine, the larvae of the green bottle fly, Lucilia sericata, are used in a procedure known as maggot debridement therapy (MDT). These sterile-bred maggots are placed directly onto chronic wounds, such as diabetic or venous ulcers. The larvae selectively consume only the necrotic, or dead, tissue, while leaving healthy tissue intact. This process is effective at cleaning the wound, removing bacteria, and promoting the regeneration of healthy tissue.