Mayflies, belonging to the insect order Ephemeroptera, are among the most ancient groups of winged insects. They possess a distinct life cycle, spending the vast majority of their existence underwater as nymphs before emerging for a brief, terrestrial adult phase. This transition between aquatic and aerial life stages results in a profound change in the insect’s relationship with food.
The Diet of the Aquatic Nymph
The nymph stage is the only time in a mayfly’s life cycle when it actively feeds, lasting from several months to a few years underwater. The diet of the aquatic nymph is predominantly herbivorous or detritivorous, consuming plant matter and decaying organic material. This long period of intense feeding is necessary to build the energy reserves required for the final, non-feeding adult stage.
Many species function as collector-gatherers, consuming fine organic detritus and silt found on the riverbed or lake bottom. Other nymphs are scrapers, using specialized mouthparts, like mandibles, to graze on periphyton—the layer of algae, diatoms, and microorganisms adhering to submerged surfaces. Certain species have evolved into highly efficient filter-feeders, using specialized structures to strain tiny food particles from the water column.
These varied feeding methods mean that mayfly nymphs play a significant role in the aquatic ecosystem by processing organic matter and serving as a major food source for fish and other invertebrates. While most are peaceful grazers, a small minority of nymphs are predatory. These carnivorous species consume smaller aquatic invertebrates, such as the larvae of chironomids (non-biting midges), demonstrating a rare dietary exception within the order.
The Diet of the Adult Mayfly
Upon emerging from the water, the mayfly enters the winged subimago stage, followed quickly by the sexually mature imago, or adult stage. Unlike their aquatic counterparts, adult mayflies do not consume food or water. Their brief adult life is dedicated entirely to reproduction, a process that relies exclusively on the energy stores accumulated during the nymph stage.
The adult mayfly lacks functional mouthparts; they are vestigial, meaning they are reduced and non-operational. In many species, the digestive tract, which was used for processing food in the nymph, is instead filled with air. This anatomical modification makes feeding physically impossible and helps to increase buoyancy during flight.
Because they cannot replenish energy, the adult life of a mayfly is extremely short, often lasting only a few hours to a maximum of a few days. This limited existence is a biological trade-off that prioritizes mating and egg-laying over sustenance.