Holding the biosphere together

At the brink of summer, the garden pond attains a chaste and balanced sort of beauty that later will drown itself in leaves. Just now, the clump of royal fern at the corner is unfurling a dozen golden croziers and the pond itself is spiked with the pink-and-white hyacinths of bog-bean (my vote for the National Flower) and the calibrated wands of horsetail.

Down at the surface, among purple whorls of mint and a bright confetti of duckweed, there is still just enough clear water to let me catch glimpses of life below. Only a month ago, shoals of tadpoles were whipping the margins of the pond to froth and I could watch three or four newts at once, swimming in slow motion through shafts of sunlight.

Now the plants have closed over, and I am left to guess at the daily mayhem that is reducing all those thousands of tadpoles to the annual quota needed for frog-replacement. In a shadow under a lily-pad, I record the passing of Dytiscus marginalis, the great diving beetle, gliding from the thrusts of its broad and hairy hind-legs, and in a gap among the duckweed its offspring, a malevolent little prawn, lifts its tail to the surface to suck air.

Both are predators, not merely of tadpoles, but of frogs themselves and even fair-sized fish. If your goldfish, orfe or shubunkins seem to have dwindled in number this spring, Dytiscus, father and son, are even more likely suspects than herons.

There are many more, and much less voracious, water beetles in the Dytiscidae family, right down to tiny creatures a mere two millimetres long, and labelled minutus or even minutissimus. All told, there are more than 80 Irish species - a mere drop in the pond, however, in the bigger world of beetles.

With the latest Irish Naturalists' Jour- nal comes a special supplement listing all the Irish beetles: I lost count at around 2,000, with another few columns to go. Britain, with its wider range of habitats and climatic conditions, has more than 4,000 kinds. But this, of course, is "nothing" again, when just one hectare of Panamanian rain forest has more than 18,000 species of beetle, most of them still without a scientific name.

This is well above Ireland's total of insects of every kind - about 16,000 species. Even so, looking down these endless lists of names, these painstaking taxonomic groupings, is it any wonder that insects have had such short shrift in nature conservation? Their very number and variety seem to numb our ecological energies.

The invertebrates (which bring in the worms and snails along with the sixlegged insects) make up, indeed, the bulk of our wildlife and biodiversity. They are found everywhere, from seashore to mountain top. Most of them are specialists, loyal to particular habitats, and using unconsidered resources (dung, dead wood) to the benefit of earth's fertility. To quote Dr Martin Speight, the Duchas research entomologist, they are "the glue which holds the biosphere together". All this should make them ideal for monitoring the countryside and for measuring the worth of the pieces we select for conservation. They will tell us how degraded or impoverished a stretch of landscape has become, and how it might be brought back to full ecological health.

Yet only very lately, with "biodiversity" the new buzz-word, are insects being inventoried at all. Flowers and birds are at least fairly easy to find and recognise and there are not, perhaps, too many of them. But, even when the long site list of beetles, spiders and flies exists, what is it good for?

Computers might have been made to cope with the myriad world of invertebrates. The right sort of database can be used to turn a site species list into a whole strategy for habitat management - this without calling in an entomologist at all. Martin Speight's favourite family of insects is the Syrphidae, the hoverflies - those lively, diverse, often brilliantly coloured creatures that dart about to pollinate so many of our flowers. His expert knowledge of the 350 or so hoverflies of the Atlantic zone of Europe, initially collated for the charmingly-named Syrph the Net Publications, has now been organised as a database for management.

In Killarney National Park, for example, Duchas has been trying to improve the ecological quality of a slope on Mangerton Mountain, covered in moorland and degraded blanket bog and grazed by deer and sheep. A stream with a few scattered, scrubby trees runs in the valley bottom. By comparing the site's list of hoverflies with species that belong to such habitats in Kerry, it has been possible to find out which insects were missing and how to attract them in.

The poorest range of hoverflies occurred on the soggy hillside covered in purple moorgrass. Grazing by deer and sheep was reducing the diversity of plants for the hoverfly larvae to feed on, and the dead vegetation was not to their taste, even when processed into dung. Replacing deer and sheep with the park's black Kerry cattle has both improved the flora and made the dung more palatable for Syrphidae. The progress of enrichment can now be followed on the database.

The park's ecologists have also been considering replacing the poorly-drained grassland by some sort of broadleaf forest that would bring diversity even closer to a natural optimum for the hillside. But should it be an oakwood, like so much of the park, or alder-willow forest, better suited to wet soil? The hoverfly list, tested against the database, showed that alder-willow would attract more new hoverfly species, both from the park and from the Kerry countryside in general.

Similar databases now exist for ground beetles, and the terrestrial and aquatic molluscs (snails and slugs, etc). Anything that enriches their variety in any habitat will be good for our environment as well.