The term “green flies” is a casual descriptor referring to multiple insect species that share a distinct green coloration. However, only one of these insects belongs to the order of true flies (Diptera). The common name often causes confusion, grouping the true fly with other distinct insects like lacewings and aphids.
Identifying the Primary Green Fly
The insect most commonly identified as the “green fly” is the Green Bottle Fly, Lucilia sericata, a species within the blow fly family (Calliphoridae). This fly is noticeably larger than the common house fly, typically measuring between 8 and 14 millimeters in length. Its most distinguishing characteristic is the brilliant, metallic sheen on its body, which can range from a vibrant emerald green to a copper-green or even a gold-green color.
The adult Green Bottle Fly possesses a short, bristly texture on its back. It features clear wings with light brown veins. As a blow fly, its robust appearance and classification mean it is among the first insects attracted to decaying organic matter.
Life Cycle and Preferred Environments
The life cycle of the Green Bottle Fly is closely tied to its role as a decomposer. It begins when the female deposits a cluster of white or pale yellow eggs on a suitable substrate. A single female can lay hundreds of eggs, usually in a batch of around 180, on carrion, feces, or decomposing meat in garbage.
Once the eggs hatch, the larvae, or maggots, emerge as legless, cone-shaped forms. They immediately begin to feed on the dead or necrotic tissue. The speed of development is highly dependent on temperature, with the larval stage passing through three instars in as little as four to nine days in warm conditions.
After completing their feeding stage, the mature larvae drop off the food source. They burrow into the surrounding soil or debris to enter the pupal stage, where they harden and transform into adults.
These flies thrive in warm, moist climates and are widely distributed across the globe, commonly found in urban environments. Preferred habitats are those with abundant decaying material, such as poorly maintained garbage bins, compost piles, and near slaughterhouses or farms. The adult flies are mobile and can be seen feeding on flower nectar, plant sap, or sugary secretions, in addition to their preferred breeding material.
Ecological Roles and Human Interaction
The Green Bottle Fly serves as a necessary component of natural processes while also interacting negatively with human health and industry. Ecologically, the larvae are powerful agents of biodegradation. They rapidly consume and break down dead animal tissue, which helps recycle nutrients back into the ecosystem. The adults contribute to pollination by feeding on nectar and moving pollen between plants.
Beneficial Applications
The insect’s biology has been harnessed for specific applications in the fields of medicine and forensics. Forensic entomologists study the developmental stage of the larvae found on a body to accurately estimate the post-mortem interval, providing a timeline for death.
Medically, the sterile larvae are used in maggot debridement therapy. They are introduced into chronic wounds to consume only the dead tissue and secrete antimicrobial compounds that aid in healing.
Negative Impacts
Negative interactions primarily involve the transmission of disease-causing pathogens and the infestation of livestock. Adult flies can mechanically transport bacteria from decaying matter to human food sources, acting as vectors for various illnesses.
The larvae can also cause myiasis, or “fly strike,” a condition where they infest the living tissue of animals, particularly sheep. This causes significant damage and economic loss to the agricultural industry if not treated promptly.
Common Misidentifications
The casual term “green fly” frequently leads to misidentification, as it is often applied to insects that are not true flies (Diptera) at all. One such insect is the Green Lacewing (Chrysoperla carnea). This is a delicate, slender insect with a pale, lime-green body and large, intricately veined, transparent wings.
Unlike the Green Bottle Fly, the Lacewing is considered a beneficial predator in gardens. Its larvae, often called “aphid lions,” voraciously consume soft-bodied pests like aphids.
Another common confusion arises with green aphids, which are sometimes called “greenfly” by gardeners. These insects are much smaller than the Green Bottle Fly, typically measuring only 1.5 to 3 millimeters long, with soft, pear-shaped bodies. Aphids belong to the order Hemiptera, or true bugs. They feed on plant sap using piercing-sucking mouthparts, often congregating in large clusters on new plant growth.