Nick Baker’s hidden Britain
Water veneer
Moths are categorically, unequivocally, not dull. Need proof? Take the water veneer, Acentria ephemerella. While it may appear ordinary, it is anything but. You can find this moth at any weedy pond in England and Wales (it’s less common in Scotland). Visit on a warm summer’s night and you might be lucky enough to see groups of males flying close to the water surface, sometimes in swarms.
Not much to look at, they’re easily dismissed as just more flimsy scraps of insect life, but don’t judge a moth by its wings! If you do, you’ll miss out on an extraordinary life story.
Between June and August, the male moths take flight on their 6mm-wide wings. The females, well, they don’t really fly at all – at least, most don’t. Therein lies one of the first fascinatingly odd things about the water veneer – there are two forms of female. One is slightly larger than the male and able to fly (no surprises there). But the more common type is wingless, or brachypterous. Technically, it does have tiny wing stubs, but the effect is the same: it can’t fly.
To have a female that is, in effect, nothing more than a bag of eggs is a relatively common strategy utilised by many moth species. However, the water veneer takes it to another level. The wingless females are totally aquatic. They spend their entire lives, from egg to adult, submerged.
In the sub-aqua world, wings are as much use as canoe paddles made of sugar paper. So, the aquatic females have exchanged wings for long-haired fringes on the ends of their second and third pairs of legs. These oars, similar in form and function to those of water boatmen (which are bugs), enable them to row around with ease. They breathe by trapping a layer of air on their body, which acts as a physical lung. Gases from the water diffuse into and out of it.
Two worlds collide
The closest the aquatic females come to the realm of air is when they move to the surface to mate with the males. Sometimes the biggest clue to the presence of a population of these insects is the tragic sight of translucent males lying spread-eagled on the surface film, having drowned after mating.
As adults, they live only a few days (hence ephemerella). Even their mouthparts, like the females’ wings, are vestigial. Once mated, the females spend the rest of their short lives laying 300–1,000 eggs. Those with wings disperse to find new weedy water – an insurance policy in case something drastic happens to their pond. It also enables different populations to mix, which limits inbreeding. Meanwhile, the wingless majority row through the water in search of weeds to lay their eggs on.
The larvae look like pretty regular green caterpillars, and set about what all caterpillars are good at: eating. It’s just that they do it underwater. They chew their way through an assortment of pond plants down to depths of over 2m, then spend winter at the bottom of the pond in a cell made of silk and leaf fragments. In spring, the chewing resumes and, shortly after, they mature and spin a sub-aqua cocoon. Here, they pupate, before starting the whole watery cycle again.