Wonderful world of song with the beetles of Pollardstown Fen

ANOTHER LIFE:CREATING OUR garden pond some 25 years ago, I blanketed the raw black plastic of its floor with a layer of earth and sowed this with roots of water plants dug out of lakes behind the shore. This rash and probably illicit strategy did, indeed, furnish the pond agreeably with rapid vegetation – bogbean, water mint, mare's tail and the rest.

It also skipped a few stages in the natural ambition of ponds to fill themselves in with decaying leaves and stems. Today, tiring in my old age of dragging superfluous biomass out of the pond each autumn, I have settled for succession to a bean-shaped fen which, left alone, might even end up as a miniature raised bog.

For a few years, however, there was still enough open water to serve the annual multitude of mating frogs and encourage soothing meditations on the antics of aquatic insects. On the surface, pond skaters dimpled the skin of the water and whirligig beetles spun in circles of shiny ballbearings. Below, great diving beetles glided through sun and shadow in pursuit of tadpoles and water boatmen rowed up and down for necessary refills of air. All this was played out in a distant, subaqueous silence, while birdsong and bumblebees strummed around my ears.

To discover the underwater sounds of the insect world – to realise they exist at all – is a mind-blowing event in one’s sharing with nature, rather like hearing whalesong for the very first time or seeing Earth from space. For that I have to thank Dr Tom Lawrence, lecturer in sound and music at Dublin City University, acoustic ecologist and brilliant wildlife sound recordist.

Two years ago, he spent six months capturing the sounds of Lough Neagh, above and below the waves, for a BBC Radio 4 natural history programme. One morning he happened to catch the sounds of corixids – lesser water boatmen – stridulating underwater (I’ll come to that). It planted a seed of deep interest in the aquatic communication of invertebrates.

This led him to the ancient wetland on the northern flank of the Curragh in Co Kildare, where thousands of hours of hydrophone recordings have now been distilled into a 70-minute CD, Water Beetles of Pollardstown Fen*. Dr Lawrence calls it “a representative sonic ontology, a phonographic document of natural history”. Less formally, he talks affectionately of the “mini-moogs” whose synthesiser-like repertoire has filled him with frequent astonishment.

The first time he dropped his hydrophone into one of the drains that feed the lake at Pollardstown, his equipment overloaded with sound. Suspecting a fault, he tested circuits, changed his mixer and fitted new cables, only to find the caco- phony still there. Only when its volume wound down and “a beautiful song” emerged, did he realise it came from a colony of whirligigs he’d disturbed at the bottom of the drain.

The recordings, with great aural presence and atmosphere, are hypnotically alien, an endlessly varying chorus of clicks, chirrup- ings, churrs, buzzes and whines, pulsating and oscillating and sometimes of startling volume (like a sudden car alarm). Individual performances go on for many hours. For the water scorpion, Nepa cinerea, at the fen’s Grand Canal springs, the hydrophone was set about one inch from the insect. It kept up an angry, oscillating rasp, sometimes of 110 decibels, for nine hours. The disc samples 13 minutes of it, amid the exhalations of plants and discourse of other invertebrates.

Each of the insects is stridulating, a term more familiar from the terrestrial world of grasshoppers and crickets. In these, the penetrating, churring sound comes typically from rubbing a series of pegs on the legs across a stiff vein on a wing. In most water boatmen, a group of teeth on the front legs is rubbed against a ridge on the side of its head. This can also interact with air bubbles stored in the insect’s body to create a “song” at frequencies that sets up a sympathetic resonance in a partner.

Last month, scientists from France and Scotland reported on sounds made by Micronecta scholtzi, a water boatman just 2mm long (and not yet found among Irish species). The pulses reached at average of 78.9 decibels, making the insect, relative to size, the loudest animal on Earth. But what also drew headlines was its manner of noise- making – rubbing a ridge on its penis across ridges on its abdomen.

That does seem to match the motivation usually accorded to water beetles and bugs – competition in attracting a mate. But research suggests stridulation serves far wider purposes, as yet almost unexplored. In redefining our notions of underwater life, says Tom Lawrence, his CD “presents a world of alarming, sophisticated communication: a myriad of signal generation perpetuated by a plethora of intelligent species”. That might be pushing it a bit, but the nuanced alertness, alarm or aggression in some of the Pollardstown “voices” seems unmistakeable.

* Available online for €17 inc pp at gruenrekorder.de/shop

Eye on nature

On holidays in Mayo I saw what I thought was a pied wagtail. But it had a whitish head, white breast plumage and its upper parts were greyer than a pied wagtail. Could it have been a white wagtail?

Peter Courtney, Co Down

The white wagtail (Motacilla alba alba) is a race of the pied wagtail (M. alba yarrellii) and they differ only slightly. White wagtails are summer visitors from continental Europe to coastal areas. You probably saw an immature pied wagtail.

I took photos of wagtails last October. When I compared them to recent photos of pied wagtails I wondered if they might be white wagtails.

Brendan O’Donoghue, Straboe, Co Carlow

Your photos showed a female pied wagtail.

We saw a small insect like a hummingbird hovering in our lavender border and dipping in to the flowers to feed. Its wings were a blur of reddish brown and it had a single bright spot on its tail end.

Marguerite O’Molloy, Crumlin, Dublin

It was a hummingbird hawkmoth, a migrant from southern Europe.

I saw this butterfly on Inis Oirr (photo enclosed).

Eddie Humphrey, Wicklow

It was a magpie moth.

Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo, or e-mail viney@anu.ie. Please include a postal address