AS I MAKE my way along the banks of the River Devon, a strong waft of sweetly-sick perfumed air fills my nostrils and I find myself submerged in a blush of purplish-pink flowers.

It is a large patch of Himalayan balsam, almost as high as my shoulders, and just one of the many invasive alien species that are now such a common feature of our countryside.

These aliens are a mixed bag, with some being rather benign whilst many have gained notoriety as serious pests.

The Himalayan balsam is very much in the latter camp. They grow tall and can shade out native species.

Their exploding seed capsules throw seeds a considerable distance, which can also be carried in the water making the plant a prolific coloniser along river systems.

But the Himalayan balsam is a mere pussycat when compared to the Japanese knotweed with its dense bamboo like stands that can totally dominate large areas of ground.

Another undesirable alien down by the banks of the River Devon is the American mink. They are one of the main reasons why water voles are so scarce, and I shudder to imagine the devastation a mink could wreak upon a sand martin colony.

Interestingly, this is the first year I can recall in recent times where I have yet to see a mink by the River Devon – perhaps they are on the decline?

But there are other less harmful arrivals by this Clackmannanshire riverbank – most notably the yellow blooms of monkeyflower which thrives on shingle banks in the river and which is a native of North America.

Earlier in the season, some parts of the river were ablaze with the pastel pinks and whites of dame’s violet, another most attractive garden plant that has now become widely naturalised in the countryside.