Insects are quietly but rapidly disappearing. Michael McCarthy explains why their loss is bad news for the planet.
The great American biologist, E O Wilson, said insects were world-rulers, but although they play a central role in maintaining ecosystems and the whole web of life, most insects have long been viewed with distaste or even revulsion as creepie-crawlies (apart from butterflies, which have been viewed as something akin to honorary mini-birds). The recent alarms in Britain, Europe and America about the fate of the honey bee – colonies have been crashing in increasing numbers – have started to open people's eyes to insects' importance in a more general way, says Matt Shardlow, director of Buglife, the Invertebrate Conservation Trust.
But it is only the beginning of an understanding, he says, and much more is needed if we are to take the action necessary to preserve our populations of insects and other invertebrates, the creatures without backbones which make up the majority of animal life, including snails, worms and spiders (spiders being arachnids, not insects).
The population declines among invertebrates in general and insects in particular are now greater than among any other group of living things, greater than declines in mammals, birds and plants. Yet although people get excited about endangered pandas, or eagles, or orchids, endangered insects generally remain below the level of their perception, Mr Shardlow says.
There is clear evidence of the sharp decline in Britain's insects, one being the disappearance of the "moth snowstorm". Anyone over 40 will probably remember that during a car journey at night in midsummer, the moths in the headlights were so numerous that they looked like snow, and the windscreen would become so coated with colliding moths that by the end of the journey it would have to be washed.
Not any more. Moth snowstorms are today moth showers, if that: the phenomenon has all but disappeared, and this is robustly backed up by the figures. Two-thirds of Britain's individual moth species have declined in the past 40 years, some by enormous amounts, and moths as a whole have lost about a third of their abundance in that period. We know this because, since 1968 the agricultural research station at Rothamsted in Hertfordshire has maintained a substantial network of moth traps around the country (at about 80 sites) to which the insects are attracted at night by a light-bulb. Types and numbers caught are carefully noted, and with long-term records for no fewer than 337 species of larger moths over four decades, this is one of the biggest sets of animal population data in the world. Analysis in 2003 showed more than 200 species had declined, and nearly 70 by more than 50 per cent. Species once well-known and abundant were tumbling: the magpie moth had declined by 69 per cent, the cinnabar moth by 83 per cent and the strikingly handsome garden tiger moth by no less than 89 per cent.
Yet it is the same story with butterflies. Thanks to another impeccably-kept set of long-term data, from the Butterfly Monitoring Scheme run by the charity Butterfly Conservation and the Centre for Ecology and Hydrology, we know that seven out of 10 of Britain's 58 species have declined in the past 30 years, some by amounts so large they are on the road to extinction.
Widespread and formerly common species such as the grayling and the wall brown have dropped in numbers by 40 per cent and more, vanishing from large areas, while others have suffered catastrophic losses. The duke of burgundy has fallen by 52 per cent, the pearl-bordered fritillary by 61 per cent, the wood white by 65 per cent and the high brown fritillary, Britain's most endangered butterly, by 79 per cent. Now there is another concern for an insect which a generation ago was the most familiar "pretty" butterfly, the small tortoiseshell. Hit hard by a parasitic fly which has come in from southern Europe, its population across Britain has dropped by 52 per cent since 1990, but in the South-east it has gone down by no less than 82 per cent over the period.
These declines are parallelled in bumblebees. Of the 25 species traditionally native to Britain, three have gone extinct, the apple bumblebee, Cullum's bumblebee and most recently, the short-haired bumblebee, and four more are designated "UK Biodiversity Action Plan species" in recognition of their precarious situation, the great yellow bumblebee, the brown-banded carder bee, the shrill carder bee and the ruderal bumblebee. Several more species, such as the bilberry bumblebee and the moss carder bee, have undergone major population contractions.
There is simply no accurate population trend data for many other groups of insects but there are ominous signs that they too are plunging. Mayflies, the river flies on which flyfishermen base their artificial imitations, appear to have dropped in abundance by about two-thirds in the past 50 years, a widespread survey of fishermen in 2000 showed. Britain's 46 species of ladybirds may now be widely at risk from an Asian invader, the harlequin ladybird, which arrived in Britain in 2004, and not only outcompetes other ladybirds for food, but eats them directly. As for beetles, there may be more than 4,000 species in Britain, but an indication of their decline is the fact that at least 250 of them have not been seen since 1970. Buglife revealed this two years ago, judging that some were merely hard to find, but others were rapidly heading for extinction. Four vividly-named species which are on the Government's Biodiversity Action Plan priority list have already disappeared: the Pashford pot beetle, the four-signed ground beetle, the Sussex diving beetle and the familiar sunshiner.
Source: The Independent, 15 November 2008
http://www.independent.co.uk/environment/nature/insecticide-an-ecologic…
- Login om te reageren