Adult mayflies have two or three long tails, and delicate wings which are held vertically over the body when at rest. The hind wings are smaller than the fore-pair and in some species are absent. Mayflies can be confused with stoneflies, caddis flies and lacewings; however, mayflies have short antennae which the others do not.
Mayflies go through incomplete metamorphosis. The nymphs have three tails and are aquatic herbivores which feed on plants and algae. Some nymphs burrow into silt, others cling onto aquatic vegetation, those that live in fast running streams cling to rocks and stones.
The mayflies are unique among the insects in that there is an immature stage that can fly. Mature nymphs float to the water surface and immediately shed their skin. The emerging insect has wings and can fly straight away; this sub-imago is dull in colour and covered in fine hairs. The sub-imago flies onto waterside vegetation where the skin is shed and the adult insect emerges. Most adult mayflies live for a day or less as adults and do not feed.
Body length from under 5 mm to 20 mm, excluding the tails.
Many species are widely distributed in the UK, but are usually found close to an aquatic habitat.
Over 2500 species of mayfly have been described worldwide, 47 species occur in the UK. A biodiversity action plan has been developed for one species, Heptagenia longicauda. Along with caddis fly and stonefly larvae, the assemblage of species can be used to assess the water quality of lakes, streams and rivers.
Where to find them in the garden
Mayflies are rarely found away from water, so are more likely to be found in gardens with ponds or with nearby, lakes, rivers or streams . Despite their name, mayfly adults can be found throughout the spring and summer, often swarming over water bodies.
Role in the garden
Mayflies have no direct role in gardens and may be considered additions to diversity. The larvae and adults are a valuable food source for fish, whilst the adults are eaten by swallows, bats and other vertebrate predators and are the models for angler’s artificial flies (baits).