Alien Invaders

When people take animals or plants to a new country and allow them to roam wild, it can sometimes create problems for the existing flora and...

November 5, 1998 12:00 AM IST

3 min read

When people take animals or plants to a new country and allow them to roam wild, it can sometimes create problems for the existing flora and fauna. Here are a few examples of good intentions turned sour:

In the late 1800s, Grey Squirrels from North America were released in England and Scotland. Now, the Grey Squirrel has spread all over Britain. And that is the problem. The animal has few natural enemies that can stop it from damaging trees. It also robs birds of their eggs and young ones. Earlier, Britain had smaller Red Squirrels which did very little damage to the environment.

The Cane Toad of South and Central America, one of the world8217;s largest toads, was recently introduced into Australia. It was thought that Cane Toads would be able to control the number of Cane Beetles, which were destroying the Australian sugarcane crop. The plan was a complete disaster. Not only did they fail to keep the number of Cane Beetles under control, they also spread across Australia, eating the native frogsand toads, small mammals and snakes. The Cane Toad too has few predators as its skin contains a poisonous substance and any animal trying to eat it would suffer a painful death.

In 1960, a fish called Nile Perch was put into three large lakes in Africa to provide food for the local people. The Perch ate so many other fish in the lakes that today, a third of the 1,000 native species of fish have become extinct.

In the early 8217;90s, an Englishman brought a pair of African Giant Snails to India. Today, Indian gardens and farmlands are heavily infested by this alien invader which has a tall-spiralled, large brownish shell decorated with dark streaks. In the absence of natural predators, this snail has infested all the regions of India where there is a good rainfall. It is known to cause much damage to vegetables, crops and garden plants. Due to its rapid breeding rate all efforts to get rid of this pest have proved ineffective.

Among the plant invaders in India, two classic examples are ofLantana and Water Hyacinth. Lantana, a flowering bush originally from tropical America, was introduced in 1809 in Calcutta as an ornamental plant. When the birds ate its berries the seeds got dispersed all over. Thus it escaped from the gardens and landed in the forests. Being highly adaptable, it can survive on both rich and poor soils. And has covered vast tracts of fertile forest land and replaced native flora.

Water Hyacinth too was brought in as an ornamental plant for its very pretty flowers. However, today it has spread to almost all tropical countries in the world, choking ponds, lakes and rivers. This plant has been a major cause for eutrophication and the early drying of waterbodies. So far, efforts to eradicate this persistent intruder have failed.