What are Mayflies

There is a common misconception that Mayflies only live for a day. Even the scientific name of the order, Ephemeroptera, gives this impression, the ‘ephemeral-wings’. But in fact Mayflies live for at least a year and sometimes two or three from the time their egg hatches to the glorious last day of their lives when they get to be an adult. Imagine not a life lived in a day but a life lived as a child for a year, followed by a single day as a winged adult, in which time you must fly, find a mate and reproduce. This roughly translates in a human lifetime as living for seventy years as a child and then maturing and getting to be an adult for about three months before a quick death. What fun, to be a child, without responsiblities for so long. Of course being human, you would know that when you matured you only had three months left to live. Mayflies don’t have that problem.

Mayflies are insects so they have six jointed legs and three body parts: head, thorax and abdomen. Insects are arthropods so as well as the jointed legs, they also have an exoskeleton and have to moult to grow. Mayflies are the most primitive order of flying insects. Below them are the apterygota, the descendents of the most primitive insects that evolved before wings, silverfish and the springtails. But insects are so successful because they took to the air, like the ancestors of the modern mayflies.

Adult mayflies have four wings, the front pair being much larger than the hind pair, large eyes and short antennae on their heads, six long legs and a ten-segmented abdomen ending in a pair of long ‘styles’ like a double tail at the end. That is what they look like, if you can get close enough, that is, because they are small and very busy in the few hours to a few days that they spend as adults.

Imagine the freedom of wings after a lifetime as a nymph in a stream. It is a good life as far as it goes, crawling about in the mud or swimming freely, picking up vegetable detritus or microscopic plants such as diatoms with claws and then eating with strong mandibles, hiding from fish, breathing with abdominal gills and every so often going through a moult Getting bigger and bigger, watching the seasons roll around for a year and then finally turning into an adult, who can fly and mate. The size of the nymph’s claws depends on the habitat it lives in. Species that live in ponds have small claws while those living in streams have short, thick claws with teeth to hold them securely against the current.

Mayfly nymphs are little bundles of protein and so are a desirable food item on the menu for many fish. Because of this, trout fishermen are probably more familiar with both mayfly nymphs and adults than most people. So mayfly nymphs do not have all that easy a time of it. Like all small animals in the food chain, they have to be both lucky and aware in order to survive for the climax of adulthood. Those who do survive have proved their worth and have won the evolutionary lottery. The prize is mating and passing on one’s genes to the next generation.

When nymphs do finally achieve adulthood, they have no mouths to eat with. That part of their life is over for good. Males often have a pair of claspers below the styles. They can mate on the wing, grasping the female with legs and claspers and then inserting the spermatophore into her genital opening. She then uses her ovipositor to deposit her eggs on the water. The eggs are attached to vegetation or other substrates by long adhesive filaments.

Mating often takes place in swarms. A summer’s day is filled with mayflies over the water, dancing about, sunlight reflecting in their membranous wings. They court and choose, mate and lay eggs. Then they die, having fulfilled their adult purpose, to make sure that there are more eggs to hatch in the spring, more nymphs to live for a year or so and then to mature for one glorious day. There are worse ways to live.

References: CSIRO 1979. The Insects of Australia. Melbourne University Press http://www.ento.csiro.au/education/insects/ephemeroptera.html http://www.bugwise.net.au/guide/mayflies