Emer­gence of mayfly pro­vides feed­ing bo­nanza


NO marks for guess­ing how mayflies got their name.

In days or yore when peo­ple didn’t have the ben­e­fit of Googling plants and an­i­mals to dis­cover their names, mayflies were the flies that be­came prom­i­nent at the end of the month of May. Sim­i­larly, the ‘May bush’ (Hawthorn) pro­duced its white flow­ers dur­ing the present month, the ‘May bird’ ( Whim­brel) passed through on mi­gra­tion and the big ‘May bug’ (Cockchafer) alarmed ev­ery­one when it ac­ci­den­tally flew into win­dows mak­ing a bang.

De­spite their name, mayflies are not con­fined to May and can emerge from April to Novem­ber de­pend­ing on the species. An adult mayfly is a del­i­cate-look­ing in­sect. It holds its long wings upright like those of a but­ter­fly rather than fold­ing them flat on its back like those of a bee, wasp or fly. It also has two or three long, thread-like tails pro­ject­ing from its rear end.

Fe­males lay eggs and like drag­on­flies they lay them in wa­ter. The eggs hatch un­der­wa­ter and the crea­ture that emerges from each egg is known as a nymph. The nymph stays un­der­wa­ter and lives a com­pletely aquatic life last­ing one or two years.

The nymph is the main feed­ing and grow­ing stage of the in­sect’s life cy­cle and is long-lived. The adults are very short-lived; their sole pur­pose in life is to re­pro­duce and to lay more eggs in more wa­ter­bod­ies to per­pet­u­ate the species. In fact, there are two adult stages, some­thing that is unique among in­sects.

To turn into a fly­ing adult, each aquatic nymph climbs up a wa­ter plant, emerges from its wa­tery world into the air, re­veals its wings as it sheds its un­der­wa­ter coat and takes off to hide in nearby veg­e­ta­tion.

The emerg­ing in­sects are the non-sex­ual, sub-imago or ‘dun’ stage that es­capes from the wa­ter and makes the tran­si­tion to the air. The dun moults into a breed­ing ‘spin­ner’ that as­cends to join oth­ers on a short-lived nup­tial flight. Males die af­ter breed­ing; fe­males lay eggs into the wa­ter be­fore they die too. The emer­gence is syn­chro­nised and the sheer num­bers of bod­ies pro­vide a feed­ing bo­nanza for wag­tails, trout and ducks.

An­glers cap­i­talise of the an­nual phe­nom­e­non by cast­ing ar­ti­fi­cial flies at­tached to hooks into the wa­ter to catch a hun­gry trout when its at­ten­tion is fo­cused on the feed­ing frenzy and when it is more likely to snap at any­thing that re­sem­bles pro­tein-rich, fast food.

The Green Drake is one of the com­mon­est of the 33 species of mayfly found in Ire­land.

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