Why do female mayflies often die after laying eggs?

Female mayflies die shortly after laying their eggs primarily because their adult stage is biologically specialized for reproduction rather than survival. Once mayflies reach the winged imago stage, they possess nonfunctional mouthparts and digestive tracts, meaning they are physically unable to feed.1

Because they cannot consume nutrients to sustain their energy levels, their adult existence is extremely brief—often lasting only a few hours or days—and is dedicated entirely to mating and oviposition (egg deposition). In many species, the female’s death is an integral part of the reproductive process; for example, some females fall to the water's surface with wings extended and squeeze out their eggs as they die. This short, intense life cycle is an evolutionary strategy that allows the species to focus all available resources on ensuring the next generation is produced.1