Mayflies produce eggs that are laid on the surface of lakes or streams where they sink to the bottom. Naiads moult 20-30 times over a period of few months up to one year or even more. They live primarily on algae or diatoms, but some species are also predatory. The lifespan of adult mayflies is very short and varies between hours and 2-3 weeks. Since the primary function of the adult is reproduction, the mouthparts are non-functional and the digestive tract is filled with air. Adults have short flexible antennae, usually three ocelli and relatively large compound eyes.
In many species, the males additionally possess very large turban-shaped dorsal eyes, i.e. greatly enlarged compound eyes that are located on top of the head. The dorsal turban-eyes are especially designed to boost light sensitivity and allow vision at low light. At dawn, male mayflies fly close to the water surface in search of females, trying to detect females against the dim background of the sky. The turban-eyes are only capable of detecting ultra-violet (UV) light. In some species (e.g. European Mayfly) the turban-eye of the male is divided: The upper portion is for seeing movement, and the lower portion is specialized for seeing details. The females have smaller eyes.