Our riverside teems with species that originate overseas, writes Ross Bentley.

Walking down Quay Lane I stopped to watch a grey squirrel as it scampered along the telephone wires overhead, using its feathery tail to balance itself and its strong claws to propel it forward. This is a creature that is perfectly evolved for high wire acrobatics; the Blondini of our local animal kingdom.
But every time I see a grey squirrel, I hold back from appreciating them fully. At the root of my aversion is the knowledge that grey squirrels are not native to Britain. They are interlopers, trespassers brought over here from North America by meddling Victorians who wanted them for their own collections or who felt our environment would be enhanced by releasing foreign species into the British countryside.

Bad guys
Ironically, as is commonly known, bringing grey squirrels across the pond has ultimately led to less diversity as a pox that they carry has weakened the native red squirrel population. The greys’ habit of stripping bark is also responsible for damaging the tree stock.
There is a part of me that can’t stop regarding grey squirrels as the ‘bad guys’. I know it is not their fault, they didn’t ask to be brought here – yet I can’t help clinging to the idea that native species are somehow superior to those that we have introduced.
But I ask myself: can such snobbery be sustained when I think of all the wildlife that we hold dear that was brought here from elsewhere?
The rabbits disappearing into the undergrowth at King’s Marsh and the hares hunkering in the fields towards Borley are themselves thought to be descendants of lagomorphs brought over here by the Romans and Normans respectively. If you see any fallow deer in nearby countryside, they will be also be descendants of animals transported to these shores by the Norman invaders in the 11th century who prized them for hunting.

Fur farms
While most would argue that these mammals have enhanced our countryside, we feel less generous towards a more recent immigrant, the American mink, which colonised our riverbanks after a downturn in the fur trade led to these fierce mustelids being released from fur farms into the wild in the 1980s. The rise of the semi-aquatic mink coincided with a drastic drop in the number of water voles, which has not evolved in symmetry with the mink, so has not developed a way of defending itself.
Unlike otters, which the water vole has evolved with, minks are narrow enough to enter vole burrows where they can decimate whole families.
Fortunately, concerted efforts by riparian landowners to trap and destroy the mink along our stretch of river have been successful while the return of the otter as waterways have become less polluted is also thought to have brought mink numbers down. All good news for the dwindling water vole population, which we hope is coming back slowly from the brink.

Foreign fauna
The banks of our rivers are also a battleground against invasive fauna. Introduced plant species such as Himalayan balsam and giant hogweed have made appearances in our locale. Himalayan balsam has lovely pink flowers, loved by our bees, but it can crowd out native species.
Giant hogweed does the same and is an incredibly impressive tall plant but it is also very dangerous as its sap has phytotoxic properties and makes skin extremely sensitive to sunlight. If the sap gets onto your skin, it can blister badly when exposed to sun and blistering can recur for years hence.

Underwater
Even below the water level, non-native species are having an impact. In recent years, rangers for the Sudbury Common Lands have seen American signal crayfish in this area. Signal crayfish carry a plague, a type of mould lethal to our rare, native white-clawed crayfish, but to which they have developed immunity.
The prize for the most bizarre non-native creature to frequent our riverside, however, has to go to the red-eared terrapin.
Sightings of this hard-shelled reptile around Lady’s Island have been reported for a number of decades. For many years there were two but about three years ago our rangers counted five in the backwater. The red-eared slider, as they are known in their native Southern United States and northern Mexico, is a popular pet and a pair must have been released when they grew too big for an aquarium or the owner got bored.
Incredibly, the sliders are able to survive our winters, slipping down into the mud as temperatures drop and resurfacing after their hibernation. They have become local celebrities and with a lifespan of around forty years, their incongruous reappearance in this corner of Suffolk as spring arrives looks could be entertaining locals for a few years yet.

Ross Bentley, Trustee of the Sudbury Common Lands Charity