Eristalis tenax, commonly known as the drone fly, is a widely distributed species of hoverfly. This insect is found across nearly all continents, excluding Antarctica, and is recognized for its physical similarity to a honeybee drone. Its unusual larval stage also contributes to its intrigue.
A Master of Disguise
The adult Eristalis tenax exhibits a notable resemblance to a male honeybee, which is the origin of its common name, the drone fly. This mimicry is an example of Batesian mimicry, a phenomenon where a harmless species evolves to imitate a species perceived as dangerous to deter predators. Despite its bee-like appearance, the drone fly is harmless to humans, as it possesses no stinger and cannot bite.
Distinguishing a drone fly from a true honeybee involves observing several physical characteristics. Flies, including Eristalis tenax, have only one pair of wings, while bees have two pairs. Drone flies also lack the constricted “waist” between the thorax and abdomen characteristic of bees, and their antennae are short and stubby. The eyes of male drone flies are large and often appear to touch each other, a feature not seen in honeybees.
The Unique “Rat-Tailed” Larva
The larval stage of Eristalis tenax is known as a “rat-tailed maggot.” Its primary feature is a long, telescopic breathing siphon at its posterior end, which functions like a snorkel. This siphon allows the larva to access atmospheric oxygen even while submerged in water.
These larvae inhabit stagnant, oxygen-poor aquatic environments rich in decaying organic matter. Habitats include drainage ditches, puddles, manure pits, and sewage lagoons. The “tail” enables the maggot to breathe surface air in low-oxygen conditions while it feeds on bacteria and other decomposing organic material.
Ecological Importance
Adult Eristalis tenax flies are generalist pollinators, visiting a variety of flowers for nectar and pollen. Their hairy bodies pick up and transfer pollen effectively, contributing to the reproduction of many plants, including some agricultural crops. They are observed on white, yellow, pink, and blue flowers, especially in late summer and autumn.
The larvae, or rat-tailed maggots, also contribute to ecosystem health as saprophages, feeding on decaying organic matter. By breaking down organic material in aquatic environments, they assist in nutrient cycling and decomposition. This dual role of the drone fly, as a pollinator in its adult stage and a decomposer in its larval stage, demonstrates its beneficial contributions to ecosystems.