Only about 10% of introduced or alien species go on to become invasive
A pair of giant African snails (Achatina fulica) was brought to India from Mauritius in 1847, by William Henry Benson, an amateur malacologist (someone who studies molluscs). He released them in a friend’s garden in Calcutta. Starting from that one pair, within a decade the snails were all over Calcutta. Today they are found across peninsular and eastern India and are a serious crop pest.
The brown tree snake (Boiga irregularis) is thought to have arrived on the Pacific island of Guam as a stowaway on aircraft around the end of World War II. Within 30 years it had caused the local extinction of 13 of Guam’s 22 native bird species.
Parthenium hysterophorus, better known as “Congress grass” is a widespread invasive weed that harms crop production and can also cause respiratory and skin allergies in people. It is thought to have arrived accidentally, in the 1950s, with wheat imported from the Americas.
Mikania micrantha, the “mile-a-minute weed,” is a rapidly growing climber that can blanket and smother other vegetation, including tall trees. One account of its introduction to India (apocryphal perhaps) is that the Allied Forces brought it during World War II to camouflage airfields constructed along the Indo-Burmese to defend against the advancing Japanese forces!
The first identified outbreak of Chikungunya was recorded in Tanzania, Africa, in the 1950s, In the early 2000s, there were widespread outbreaks in India and across the Indian Ocean islands. It has since also spread to other parts of Asia, the Caribbean and the Americas. Its spread across the world has been related to the expansion of its vector, the invasive mosquito, Aedes albopictus.
Just as a number of plants and animals introduced to India from elsewhere have become invasive here, several Indian species have become invasive in other parts of the world. Some examples include:
The Himalayan balsam (Impatiens glandulifera), which was introduced to Europe and North America as a garden ornamental. It forms dense stands, suppressing native biodiversity and is now considered an invasive species.
The small Indian mongoose (Urva auropunctata) is an invasive species on many islands in the Pacific and the Caribbean, where it was introduced to control venomous snakes and rats in sugarcane plantations.
The red-vented bulbul (Pycnonotus cafer) is an invasive species in Fiji and Hawaii. It destroys fruit crops, displaces native birds, and aids in the dispersal of invasive plants such as Lantana.
Mapping Invasive Alien Plants: a pilot effort to create an invasive plant atlas, supported by a grant from the National Geographic Society.