The Mayflies are a nearly cosmopolitan and primitive order of wings insect. The nymphs of all species are aquatic and need unpolluted freshwater. Adults are only short lived and tend to stay around water sources. They often form obvious swarms over the water in summer. The adults do not feed. Most adult mayflies have 3 cerci (“tails”). They have large compound eyes and two pairs of wings, with the hind wing much larger than the fore. When at rest mayflies hold their wings vertically above their body. Mayflies have two life stages of being winged. The first is when they just emerge from the nymph and lasts about one day. This is called sub-imago (fly fishermen called this a dun) and it is a dull colour and the wings are opaque. They sit on plants at the side of the waterway until the next moult. The final moult, leading to the imago, is when a layer from each of the wings is lost, causing them to become transparent. At this stage mating occurs.
Nymphs have well developed legs and cling to rocks in the water body. They have fully functioning mouthparts and digestive system and feed on detritus, algae and diatoms. Depending on species the mayflies may remain in the nymphal stage for weeks ranging to years. Mayfly nymphs are an important food source for fish and other carnivorous insect nymphs such as dragonflies. Spiders, birds, mammals and amphibians feed on the adults.
References
Gooderham, J & Tsyrlin, E 2002, The Waterbug Book. A guide to the Freshwater Macroinvertebrates of Temperate Australia, CSIRO Publishing, Collingwood.