Oh! to be a stick insect

Small flickers of left-over colour enliven a garden now settling down, at last, to sleep: little flames of nasturtiums, a sunny disc of marigold, a solitary spire of delphinium. Under the leaf litter, daffodil leaves have been sprouting. A friend clearing a ditch at the other side of the hill found frogspawn on November 15th, three months ahead of schedule.

Butterfly-watchers have been totting up their records for the autumn's late flyers. No fewer than 17 species were still on the wing in these islands last month, including a red admiral at Athlone on November 23rd. Six days later, a squadron of pipistrelle bats, which should have been hibernating, were still catching flies at dusk above seaweed rotting on the strand at Bray, Co Wicklow.

So yes, strange events in an autumn of record warmth, hinting at changing patterns as global warming takes hold. Some songbirds are already nesting in early spring, weeks ahead of the usual average, and a Skerries reader was startled to see a pair of starlings apparently mating on November 25th.

Out-of-season courting behaviour has to be judged with care. Blackbirds, robins, starlings all pair up in late autumn and go in for a bit of sexual chasing. A cock starling will even carry nest material into the hole. But actual mating, so crucially linked to seasonal food supply, is timed by hormones in response to changing day-length - or so biologists agree. Can a sudden insect "bloom", keyed to temperature, trigger such aberrant behaviour? Sorting out real trends from oddball events will not be easy.

We've yet to see the effect of warm, wet winters on insect life and thus on the food available, not only to birds but to foxes, badgers, shrews, hedgehogs and bats. As a gardener, I'm all in favour of a few weeks' bitter cold in winter as a natural shriving of the ecosystem. It will not feel the same if fungal disease takes over control of aphid and other pest populations.

A good many insects overwinter in the egg stage of their life-cycle, armoured against anything the weather brings. Among them are some of the smaller bugs, but the contrast between size of egg and the adult insect can sometimes be startling.

Ireland's biggest leaf-eating insect is a good five inches (12.5 centimetres) long, but its young are hatched from eggs a mere 4mm across. Even full-grown, however, the unarmed stick insect, Acanthoxyla inermis, can be invisible right in front of your eyes.

Just now, as it happens, is a good time to go looking for the beast at its very local haunts in the south-west of Ireland. As the wind strips the last leaves from the shrubs, some bare twigs start walking, searching for what may well be the last meals of their brief lives.

Ireland's stick insects are among nature's most intriguing masters (or rather, mistresses) of camouflage.

Originally arriving as eggs in soil among exotic tree ferns imported from New Zealand, they have become naturalised in the mild, moist climate of Kerry and Cork. The first scientific record dates to the 1960s, but the insect's precise species was identified only a few years ago, and its full distribution in the south-west is still unknown.

Outside New Zealand, the insect is found only in Ireland and in south-west England. In both areas, the source was the same: Treseder's nursery in Truro, Cornwall, early specialists in bringing Australasian plants to Europe. Among Treseder's "big house" customers a century ago was Viscount Mersey, with estates around Kenmare Bay in Co Kerry, where several colonies of stick insects now flourish.

It was at Rossdohan Island, with its lushly-furnished "sub-tropical" garden, that the insect was first recorded. A. inermis is flightless and static, and needs humans to spread it around, either by moving plants which happen to have eggs among the roots, or through children finding the adults and taking them home.

By such means, Ireland's insects seem now to have reached West Cork. The exact spread of the species is of deep interest to one English naturalist, Malcom Lee. With stick insects living in his garden in Cornwall, he has been studying their history and distribution for a decade.

The unarmed stick insect lacks the spiny defences of the prickly stick insect that also occurs in Cornwall (as does the smooth stick insect, long thought to be the species in Ireland). It is one of the phasmids, an order of "phytophagous, nocturnal, arboreal or arbusticulous, orthopterodean insects found mainly in wet tropical habitats" (this from my Dictionary of Natural History, which is supposed to help). It is also parthogenetic, which means it doesn't need a male to produce fertile eggs. Indeed, one stick insect can found a thriving colony all by herself, scattering some 200 eggs at random during her brief lifetime. These fall to the ground and hatch the following spring into half-inch nymphs, which have only to climb the plant from which they fell to start eating the right kind of leaves.

Far from needing tree-ferns or exotic vines, A. inermis is quite happy with brambles, rose-bushes, fuchsia or even heather (which is where friends of mine saw one near Rossdohan in 1997, the most recent of reported sightings).

Birds and wasps make a necessary massacre of nymphs, and few of those which expand, at such an astonishing rate, into adults, will make it through the winter. As the leaves fall, they may sometimes be found clinging to a house wall for warmth.

Last winter, a lady at Falmouth in Cornwall tidying up her hedge was rather shocked to see her "clippings" start into life and walk away.

Unlike a more recent import from New Zealand, the predatory flatworm Artoposthia triangulata, the unarmed stick insect is utterly benign and a welcome curiosity among Ireland's fauna.

Malcolm Lee would much appreciate a record of any sightings, new or old, with which to update his research. A map grid reference for the location would be a bonus. He is at Gullrock, Port Gaverne, Port Isaac, Cornwall (e-mail: gullrock@ukonline.co.uk; tel: 0044-2108-880108).