ANOTHER LIFE:THIS COULD BE the summer the dreaded harlequin ladybird, Harmonia axyridis, invades Ireland, borne on an easterly wind or crouched in a box of British carrots, its mandibles bared not only for Irish aphids but all manner of our native insects. What it does not out-compete, it will eat. Such was the message of the media's big environment story the other morning.
The sudden fuss about the harlequin’s rapid spread the length of Britain, potentially “threatening” more than 1,000 of the UK’s native species, was partly to bring visitors to a particular stand at the Royal Society’s summer exhibition in London. Scientists know a good story when they have one and need the public’s help. But given the Asian ladybird’s meteoric expansion in Europe and North America and from Essex to Orkney in only four years the concern is legitimate enough.
When – not if – the harlequin takes hold in Ireland, it will join a long list of invasive aliens: zebra mussel, roach, pike, curly waterweed, azolla water fern, sargassum seaweed, gunnera (“giant rhubarb”), rhododendron, giant hogweed Japanese knotweed, Himalayan balsam, American mink and grey squirrel, sika, fallow and muntjac deer, Australian and New Zealand flatworms, and many more species of lesser notoriety.
Go to InvasiveSpeciesIreland.com and inspect the “most unwanted” among potential threats. The harlequin ladybird leads the field, and reports of it are eagerly solicited.The first specimen to reach Ireland was found in 2007 in a Lisburn shop among celery from Cambridgeshire. But so far as the National Biodiversity Data Centre in Waterford is aware, none has yet been found in the wild. It is rounder and larger than Ireland’s familiar seven-spot ladybird, and can be orange with 15 to 20 spots, as in the drawing, but also black with two orange or red spots or black with four orange or red spots. This variable livery has helped it on its way.
Like many other disastrous introductions in world history, the harlequin seemed a good idea at the time – a ladybird with such a huge appetite for aphids (12,000 per beetle per year) seemed a perfect biological control for the main pest of greenhouse and polytunnel crops in continental Europe and North America. Unfortunately, having flown out the door, it set about eating from a far wider menu, including the larvae of moths, butterflies and native ladybirds.
In less than two decades, it became the commonest ladybird over large areas of the US, and its swarms have caused panic in American city buildings, triggering smoke alarms and penetrating computers. When infesting vineyards, its defensive chemical “juice”, common to all ladybirds, has tainted the wine.
It’s the harlequin’s threat to biodiversity, however, that has a team of UK scientists, led by Dr Helen Roy of the Centre for Ecology and Hydrology, looking for a natural enemy. Its evolution in Asia seems to have given it resistance to fungal diseases and parasites that attack ladybirds native to these islands. The team are exploring the insects’ message-carrying chemicals, which may offer ways of luring them into traps.
Thanks to human activity, from shipping and long-distance lorries to aquaculture, horticulture, gardening, leisure boats and angling clubs, Ireland – like most of the world – abounds in alien species. Some of these become invasive – smothering or choking native habitats, transforming ecosystems, preying on native species or out-competing them for food. The new international concern for loss of biodiversity has made control of invasive species a priority, backed up by agreements and EU directives.
In 2004, Quercus, the Northern Ireland research centre, made an all-Ireland report on invasive species to the conservation agencies north and south, and risk assessments have been carried out for 385 established species and 171 potential invaders.
Weighing up their impacts, ecologically and economically, can be complex. The sargassum seaweed, for example, competes with native species, clogs up marinas and aquaculture beds, but also colonises inhospitable areas, giving new shelter to young fish and crustaceans and boosting fishermen’s catches.
The New Zealand flatworm, however, is reckoned straightforwardly “the most serious predatory introduced species in Ireland”, given its appetite for the earthworms that keep our soil aerated and fertile. The best account of it, by Dr Roy Anderson, is found at habitas.org.uk/invasive/species.asp?item=40818.
Arriving in Northern Ireland half a century ago, probably through the plant trade, it is now “almost everywhere” in the northern counties, emptying gardens of their larger earthworms and frequently reported from farmland. But, says Dr Anderson, “its impact in agricultural land is unclear, as earthworm populations in open fields seem to recover quickly from flatworm predation”.
In the Republic, south of a line from Donegal Bay to Carlingford Lough, it seems to be confined, so far, to gardens and garden centres. Its preference for cool, moist soil and humidity may bring an ultimate control, islandwide, through climate change.
EYE ON NATURE
I watched a line of rooks queuing to take their turn on my neighbour's chimney. The incumbent squats over the smoking chimney, fluffs his feathers and preens while those in the queue squawk to say hurry up.
Terri Kearney, Skibbereen, Co Cork
We watched two jackdaws taking turns to stand in the smoke from our neighbour's chimney, with wings outspread like a cormorant drying itself.
June Hurley, Killiney, Co Dublin
The rooks and jackdaws are getting rid of parasites.
At the edge of the Marina Pond we saw a duck with 20 chicks. They all seemed to be of the same age and we wondered if some had been adopted.
Michael and Margaret Gavin, Cork
Ducks have creches where a mother duck will look after the broods of others.
Green caterpillars are eating the young leaves of silver birch trees. Is there an environmentally friendly solution? Niamh Hearns, Balla, Co Mayo
These are not caterpillars but the larvae of a birch sawfly and you should spray them with pyrethrum as they will pupate in the soil underneath and may produce another brood this year.
Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo. E-mail : viney@anu.ie. Include a postal address.
