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Dangerous aliens: a risk worth taking?

Friday 12 March 2010

Our countryside commentator John Sheard, who has spent hours disentangling his trout flies from clumps of Japanese knotweed on the banks of various North Country rivers, wonders if introducing yet another alien – a sap-sucking bug – to tackle the problem is a move we might rue in the future

OVER the years, there has been an often bitter debate over where there is other life out there in space and, if so, should we try to make contact with it? The Americans have been probing the universe for years to make such contact but there are others who warn that such aliens might in fact be a lethal threat to mankind, the mythical invaders from Mars.

Now I am not much of a science fiction fan – not since John Wyndham’s Day of the Triffids, that is – but over the years I must have written hundreds of thousands of words about the real life dangers of introducing alien species to this green and pleasant land of ours.

Japanese knotweed
Japanese Knotweed

t has been going on for centuries. There is some dispute over this but either the Romans or the Normans introduced the rabbit and, after my allotment has been ravaged from time to time by the little so-and-so’s, my curses are thrown back over the millennia. But my problems are as nothing compared to their introduction to Australia: there, they ransacked an entire continent.

The introduction craze really took off in Victorian times, when plant collectors scoured the world for new garden species and, and the same time, status-conscious wealthy garden owners brought in cuddly little creatures like the grey squirrel and the tiny muntjac deer.

We all know what the grey squirrel did to our native reds but the muntjac is also a menace in various parts of the Yorkshire Dales, having run wild for decades and has become a specialist at destroying gardens and tree saplings with an alacrity that makes the humble jack rabbit look lazy.

Despite these warnings from the 19th Century, we have continued to introduce dangerous aliens almost to the present day: mink, brought in for fur farms, were “rescued” (released) by animal rights enthusiast and proceeding to wreak untold havoc on our countryside, killing kingfishers, water fowl and Ratty, the water vole of Wind in the Willows fame.

Aphalara itadori
Psyllid Aphalara itadori Photo: DEFRA

More recently, they brought in the American rainbow trout, which escaped into our rivers to compete with native brownies but which do not breed in the vast majority of our rivers – so when they die, that waterway is left troutless.

The most recently introduced “farmed” species was the American signal crayfish, which also escaped, and is now expanding along Yorkshire Dales rivers like the Aire at astonishing speed, killing off our native crayfish on the way. It is a long and sorry list – but is it about to become longer and sorrier?

One of those Victorian horticultural imports was Japanese knotweed, a pretty plant with white and pink flowers which just loves our English river banks. And how: it now dominates thousands of miles of them and expands it territory year on year: I know, because I am forever snagging my fly fishing back cast on them on stretches of water which, only last season, was completely clear.

Knotweed is even more difficult to destroy than John Wyndham’s Triffids. It can grow through concrete and, according to the environment department Defra, is costs some £50 million a year to pay contractors to dig it out – often using JCB’s – because it is virtually impervious to modern herbicides.

Knotweed is even more difficult to destroy than John Wyndham’s Triffids...

So this week, Defra announced that, after years of trials, it was permitting the release of a tiny little bug called a psyllid which, despite its miniscule size – about the length of two grains of sand – it a mighty killer via its even tinier larvae, which munch away at the knotweed until it has sucked the plant dry (See News).

The psyllid is a native of Japan, where it controls the spread of the weed, and – says Defra – long term tests have been carried out here to show that it will only attack knotweed and all our native plants are safe from its greedy little jaws. Its release will be the first time in Europe that a large scale, natural control method has been used.

Well, I hope the scientists know what they are talking about – and there has been a lot of controversy about dodgy science just lately. And I can’t help thinking about the Australian cane toad, one of the biggest natural control disasters ever launched by man.

The toad, a nasty, warty beast which can grow to weigh almost five pounds, was introduced to Australian sugar cane plantations from South America because it ate the sugarcane fly in enormous numbers. So it did - and it just loved life Down Under.

There are now hundreds of millions of them and they can swamp the roads so deep that drivers squash thousands of them as they drive along. They, too, are difficult to eradicate: they give off a cocktail of poisons to strong that they can kill a dog if it tries to eat them. At least our new “welcome” alien is pretty small – but I shall be keeping a sharp watch on the river bank for the next few years.

Feedback received on this subject:

A key criterion set by the conservation industry for determining if a species is “native” is that it should have evolved with all other species within its own ecosystem and not have been introduced or assisted by man to arrive at what is regarded as its natural location. In short, it should have got to where it is by its own efforts and evolved naturally. If man assisted it, it is regarded as “non-native”.

This is confirmed in Scottish Natural Heritage’s website:

“3.5. Native species are presumed to be those that are present in Great Britain by natural means. In general they migrated (or were transported by other species) into Great Britain after the last Ice Age, without the assistance of humans.”

“3.6. Non-native species have been introduced to Great Britain, either deliberately or accidentally, by humans.

However, this criterion is profoundly flawed and is only credible if the actions of humans are wrongly regarded as outside of nature.

There is no doubt that in the animal world we are pretty smart cookies. We have evolved to manufacture modes of air, sea and land transport, store extensions of our memories on computers, provide ourselves with heat and light, cut ourselves open to remove diseased tissue, grow our own animal and vegetable food, and destroy other members of our own species with unimaginable ferocity if they dare to compete with us for desirable objectives. But none of this excludes us from nature. It only shows we have the mental and physical capacity to use tools and weapons made from natural resources to a greater degree than any other species on the planet. So as we are part of nature, it follows that if we transport fauna or flora to our homeland because we find them attractive, then the claim that these introductions are only acceptable “if transported by other species” is exposed as anthropocentric prejudice, masquerading as science, which serves to undermine the whole concept of native and non-native species.

In fact, the survival of all species depends almost solely on their attractiveness to other members of their own species, and in many cases their attraction to other species as well. It is ironic that that attractiveness, which is leading conservationists to “protect” the red squirrel, was the reason for introducing grey squirrels in the past.

Conversely, it is equally ironic that both red and grey squirrels have been demonised as “tree rats” at different times, which has led to tens of thousands being slaughtered because they were intensely disliked for similar reasons. 80,000 red squirrels were killed in Scotland early in the last century by those with forestry interests who blamed them for tree damage.

Also, if it is important to conservationists that a species evolves naturally over millennia in Britain to earn its “native species” status, then it should be equally important that the same species evolving in a different natural environment abroad should not be regarded as “native” to this country. They can’t have it both ways! But they try.

It is well known that the grey squirrel was brought from America to England in the late 19th Century but less known that ancestors of the current population of red squirrels in the UK have been largely introduced from various parts of Europe. These animals evolved within a wide range of climatic and environmental conditions and associated with different flora and fauna encountered across the part of the range they inhabited, so for conservationists to argue that these influences are not important is to argue against their own concept of “native species”.

Both current populations of squirrels, red and grey, have been introduced to this country and there is no evidence that even the earlier red squirrels evolved here continuously from the time of the land bridge to Europe around 10,000 years ago. Scant archaeological snapshots give no indication of a continued presence. Indeed, prior to the 15th century there seems to be no record of the continuous existence of red squirrel populations living in Britain.

“There is no longer a ‘native’ red squirrel due to the frequent introductions from Europe and habitat defragmentation which has allowed gene flow between previously sub-divided populations.” (Harris et al, 2007)

Angus Macmillan Balloch

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