Oriental Invaders

Brown furry appendages on their claws give the Chinese mitten crab their name.  The young larvae probably hitched a ride to Europe in ships’ ballast water. Once here the unwelcome visitors prey on salmon eggs and fry, and destructively burrow up to half metre into river banks causing collapse.  They spread rapidly because they can cross dry land and can migrate up to 1,000km while growing to size of a dinner plate. A delicacy in their native China, scientists are checking to see if the animals that have taken up residence in our rivers are safe to eat.  If they are, we might be able to fish or trap them and gobble up  the problem crustaceans.

 

Great Pic of mitten crab and dinner plate avail from Nat history museum

 

Day of the Triffids

First planted as an ornamental by Victorian gardeners, the giant hogweed jumped the garden fence and is a real pest now. Similar in appearance to cow parsley but 7 times the size at up to 6 metres tall, it is illegal to plant.  Its huge leaves shade the ground underneath and kill off other plants. When it dies back in winter, the bare ground can cause erosion, especially of river banks.  Each plant can produce 50,000 seeds a year, which can lie dormant waiting for a suitable chance to germinate for up to fifteen years.  It is so invasive that companies have to follow special waste disposal rules for dumping soil that might contain hogweed seeds.  It is also poisonous and skin contact with its sap can cause nasty sun sensitive blistering.

 

Molluscan monsters

Inedible eastern European zebra mussels are causing havoc in our water pipes.  The freshwater mussels grow in thick layers one on top of the other, and clog up everything from power plant water intakes to valves and drains, and can damage piers and boat hulls.  A number of boats in the Thames crashed last year because their propellers were covered in zebra mussels.  Though small, their rapid growth means that they outcompete our native shellfish.   They can be controlled by environmentally unfriendly chlorine, but will clam up if they sense it.  Researchers are working on a poison pill approach by coating potassium chloride in globules of vegetable fat.  The salt is deadly to zebra mussels but safe for other river life.

 

The harlequin has landed

Our native ladybirds are threatened by the most invasive ladybird on earth.  The big, multi-spotted, and multi-coloured harlequin ladybird took less than twenty years to conquer the whole of North America.  The originally Asian insect eats so much greenfly that it leaves little for our UK species when they are competing side by side.  The natives then starve.  And worse, once the food runs out the harlequins will turn cannibal and eat the locals. The secret of its huge success is that harlequins can produce two generations a year, so that 1 female could produce 1.6 billion offspring in just two years.  It was only first spotted here in the summer of 2004.  Most commonly orange with 15 – 21 black spots or black with two large red spots, harlequins have pale legs unlike most British ladybirds.

 

 

Slim and grim

The weasel-like, dark brown furry American mink is an escapee from fur farms where it was raised for its fur.  Vicious and voracious, its spread throughout the waterways of the country has caused a disastrous decline in native water vole numbers.  Ratty the vole, of Wind in the Willows fame is defenceless against the mink as the slim animal is able to squeeze down its burrows and will eat the vole literally out of house and home.  Mink will even line their nests with vole fur, along with grasses and straw.  There is hope though.  Otters are making a comeback as they recolonise our cleaner rivers.  The larger otter will drive out mink from areas where they live together, so the vole numbers are recovering as mink are forced away from Ratty’s river bank home.

 

Fatal fungus

First discovered in the Netherlands about a hundred years ago hence ‘Dutch’ elm disease, the killer fungus actually came in from North America on infected furniture and timber. Spread from tree to tree by our native elm beetle, it blocks the water vessels of the plant causing it to wilt and die.  In twenty years, 17 million of England’s 23 million elm trees were killed in the epidemic, changing the face of the British countryside.  Few areas keep their elms, like Brighton, where the beetles have not yet carried the disease. Resistant hybrid trees are the only hope, but they look different to the native British elm so our countryside will never be the same.

 

Slimy slugs

Spanish slugs are a slimy menace originally from the Iberian peninsula in Spain.  They have spread north and probably reached Britain on imported plants.  The slug is hermaphrodite. One animal has both male and female sexual parts.  So it doesn’t even need a mate to breed. And just one slug can produce 100 eggs at a time.  In Sweden they are known as murder slugs because they kill other slugs.  A major pest of crops from potatoes to strawberries, a particular favourite, where they can eat up to half the crop.  Horticulturalists can control them using a parasitic worm, which delivers bacteria into the slug and stops them from eating.  The brown or orange nocturnal slug can grow up to a massive 15 cm long, not something you want to accidentally step on in the garden.  

 

Squawking parrots

Ring-necked Parakeets are bright green Indian members of the parrot family.  This bird has made itself at home in the South east of England after escaped pets began to breed here in 1969.  Esher Rugby club is home to London’s biggest roost, which has up to 6,000 of the birds.  The 16 inch parakeets are attractive, with the males having a pink ring around their neck. You wouldn’t want to be living near a big roost as thousands of the squawking social birds can make a lot of noise.  The RSPB believes that there are now around 30,000 in the capital and expect them to number 50,000 by 2010.  They are a pest on fruit crops, ripping off the buds for food.

 

Marauding mammals

Not a true alien visitor to our shores, wild boar did live here until they were hunted to extinction 300 years ago. New wild populations are escapees from farms where they are raised for their meat. Many were deliberately released by animal rights activists.  One group of about a dozen animals is currently terrorizing the residents of Dartmoor where an eighty year old granny recently had to rescue her daschund from three of the tusked hairy pigs.  The tasty wild mammals are not usually a threat to humans but are capable of digging up fields and forests in their search for food with their tusked snouts.  Females form groups called sounders and can be dangerous when defending their cute-looking striped piglets.

 

Over sexed and over here

These small, plump and attractive chestnut ducks were imported from America to enhance wildfowl collections. Ruddy ducks arrived at the same time as US soldiers during the war, but stayed.  The attractive escapees took such a fancy to mating with the Spanish White headed duck that European males did not stand a chance and now the species is threatened with extinction due to cross breeding.   A controversial cull costing £5 million is due to wipe out the transatlantic interlopers.  One animals rights campaigners said that it would be cheaper to fly the birds back to America via business class than to shoot each one.  But quite how he planned to get them to check in at Heathrow is a mystery.