Mayflies belong to the order Ephemeroptera, ancient insects tied to freshwater habitats. Their name comes from the Greek word ephemeros, meaning “short-lived,” which describes their brief winged existence. The mayfly life cycle involves a lengthy aquatic phase and an extremely short terrestrial phase. This unique history means the diet varies drastically between immature and mature forms, with feeding occurring almost exclusively during the time spent underwater. The nymph stage, which can last from several months up to a year or more, is the period of active consumption and growth, while the adult stage is dedicated entirely to reproduction.
The Exclusive Diet of the Aquatic Nymphs
The majority of a mayfly’s life is spent as an aquatic nymph, or naiad, feeding and accumulating energy reserves. Nymphs are classified as herbivores or detritivores, consuming plant matter and decaying organic material. Their diet is diverse and depends heavily on the specific species and their microhabitat within the stream or lake.
Many species are scrapers or grazers, using specialized mouthparts to ingest periphyton—a complex layer of algae, diatoms, and microorganisms—that coats submerged surfaces. Other nymphs function as collector-gatherers, sifting through fine particulate organic matter (FPOM) and detritus that settles on the stream bed. Burrowing nymphs, such as those from the Ephemeridae family, are specialized collector-gatherers that feed on organic particles dispersed within the substrate.
A third feeding strategy involves filter-feeding, where nymphs utilize dense fringes of setae on their legs or mouthparts to capture suspended particles from the water current. Species like Isonychia use their forelegs as a collecting net to snag minute food items like plankton and fine detritus. While most nymphs consume plant material, a few larger species have evolved to be carnivores, actively preying on smaller aquatic invertebrates.
The Adult Stage: A Short Life Without Feeding
Once the aquatic nymph emerges and molts into its winged form, feeding ceases entirely. Adult mayflies, including the initial subimago stage and the final reproductive imago stage, lack functional mouthparts and a digestive system. Their anatomy reflects this change, as internal resources are redirected solely toward the demands of flight and reproduction.
The energy requirement for the adult’s brief life is met by fat reserves built up during the nymph stage. This banked energy sustains the subimago and imago for mating. The adult stage lasts from only a few hours to a maximum of a few days, making it one of the shortest life spans of any insect. This non-feeding existence allows the mayfly to focus its limited time entirely on reproduction.
Ecological Impact of Mayfly Feeding
The grazing and collecting habits of mayfly nymphs position them as primary consumers, playing a significant role in the flow of energy within freshwater ecosystems. By consuming algae and detritus, they effectively transfer energy from the lowest trophic levels to higher ones. This conversion makes them a valuable food source, rich in protein and essential amino acids.
Mayflies are a key part of the diet for numerous predators, including fish, particularly trout, birds, bats, and other aquatic insects. The mass emergence of adults, known as a hatch, creates a temporary but massive food pulse that triggers intense feeding activity. Furthermore, because mayfly nymphs are highly sensitive to pollution, their presence or absence serves as a reliable biological indicator of water quality. A healthy population of diverse mayfly species signals a clean and stable aquatic environment.