Hidden Britain
REVEALS A FASCINATING WORLD OF WILDLIFE THAT WE OFTEN OVERLOOK.
Green drake mayflies y form dancing flocks
There seems to be almost nothing to them: a gauzy hint of life, a diaphanous spectre on the periphery of your vision as you stroll by a river. Unless you’re an angler, mayflies tend to flutter by unnoticed, and what’s more, most of the 51 British species are tiny, with a body length fewer than 15mm. Their winged life is short too – a matter of hours to a few days.
This month the green drake is on the wing. Not only is it the biggest British species, it also lives longest, so is the one most likely to be noticed – its visibility is what gives mayflies their name. Over a healthy river on a languid spring evening, green drakes can form incredible dancing flocks as the females waft their heady perfume and attract the males, a dancing behaviour that earned them the anglers’ moniker of ‘spinners’.
The nymphs of these mayflies, called naiads, spend 1–3 years developing in sediment at the bottom of clean rivers, streams and lakes. Here they feed on organic detritus and go through 30–50 moults. This life stage reminds me of Chinese dancing dragons. You’ll see what I mean if you excavate a nymph from its silty lair and witness the six pairs of hairy gills pulsating on its flanks, together with the horns and tusks on its head. Keep nymphs in an aquarium and as they reach the end of their aquatic life you might notice them change behaviour. They burrow less, sit on top of the sediment and take on a silvery appearance, as if liquid mercury is running beneath their skin. This is air, and it’s causing them to become slowly more buoyant. The middle portion of their gut, which degenerated after they ate their last meal, has turned into a sausage-shaped flotation device that now fills with air. Eventually they bob to the surface.
Change of scene
Almost as fast as they hit the surface, like actors changing between scenes, they undress. It starts as a split along the back and then they unzip. In a matter of 30 seconds or fewer, they’re out of their old clothes and exposing their new look, with fully inflated, functional wings. These translucent visions pause on the water before flying off, leaving the shadowy husks of their former life to drift away.
The winged stages are known as s duns, due to their dull, ye ellow-brown hue and the fuzz of f unwettable hair on their wings an nd body. Now they perch on waterside w vegetation to await the next n transformation. Their sexual or rgans, among other things, still h ave some growing to do – and, unique u in the insect world, they ar re about to moult from one winged w form into another.
After a few hours each dun ru uptures, and out of the seam co omes another. Its wings are the most m surprising thing: they are cr rystalline and sparkle in the su un, with darker veins that give a da appled beauty. At the same time, th he male’s front legs are longer th han before and the triad of tails al lmost a third as long again.
Why have a second moult? T The truth is nobody really kn nows. Perhaps the process has b een carried over from more p rimitive forms of mayfly. Or maybe m a mayfly’s adult life is to oo short for it to have been se elected out of existence? Since th his stage lacks mouthparts an nd its body cavity is full of f reproductive organs not di igestive systems, it only has th he fat reserves laid down as a nymph n to power it through its br rief love life, culminating in a clutch of 8,000 fertile eggs sc cattered by the female to the fa ate of the current.