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Scotland has been invaded by 988 alien plant and animal species, according to
Scottish Natural Heritage, which has carried out one the most extensive studies
of its kind. Some 41 per cent of species are a threat to native wildlife. They
include the American mink, the New Zealand flatworm and the rhododendron, which
smothers ground plants and prevents trees from seeding. But many of the aliens
do no harm. These include a 30-strong colony of red-necked wallabies that
escaped from a private collection on the small island of Inchconnachan in the
middle of Loch Lomond in 1975.