News > Press releases > Alien Species Invade t ...

Press releases

Alien Species Invade the Planet

Gland, Switzerland, May 2001 - The crazy ant, the brown tree snake, the small Indian mongoose, the Nile perch, strawberry guava, the water hyacinth, the zebra mussel and the brushtail possum are all wonderful species in their own habitats. But like an unwanted guest they can be a pest when they invade ecosystems to which they are alien. In fact these species have inflicted enormous environmental and economic damage throughout the world when they invaded places to which they were not native.

These eight invasive offenders are among a 100 of the worst alien species, according to a report just issued here by IUCN - the World Conservation Union.

Invasive alien species are those that occur outside their natural range and threaten the existence of native plants and animals and ecosystems.

"After habitat loss, this biological invasion constitutes the greatest threat to biodiversity, and it has already had devastating consequences for the planet," says Dr Jeffrey A. McNeely, IUCN's Chief Scientist. "The economic bill runs into tens of billions of dollars every year. Pests, weeds and pathogens, introduced deliberately or accidentally, reduce crop and stock yields, and degrade marine and freshwater ecosystems."

Quite aside from the publication of the booklet-report, "100 of the World's Worst Invasive Alien Species," Dr McNeely points out, Tuesday 22 May is Biodiversity Day. "It will be celebrated all over the world. The emphasis this year will be on how to cope with this alien invasion, not from Mars, but from our own planet."

Consider what havoc these invaders have wreaked.

Crazy ants, so-called because of their frantic movements, have invaded native ecosystems and caused great environmental damage from Hawaii to the Seychelles and Zanzibar. On Christmas Island in the Indian Ocean they killed three million crabs in 18 months. These red land crabs played an
important role in the island's forest ecosystem by eating leaves and seedlings of rainforest trees. Crazy ants also prey on, or interfere with, the reproduction of a variety of reptiles, birds and mammals on the forest floor and canopy.

The brown tree snake lived naturally in Australia, Indonesia, Papua New Guinea and the Solomon Islands until one day in the late 1940s or early 1950s it apparently "hitchhiked" to Guam on a military aircraft. The lack of natural predators and the presence of ample prey allowed the brown snake
population to explode. By the 1970s this poisonous reptile was found island-wide and had done extensive economic and ecological damage. It has caused major power outages across the island and sometimes bites people, but is most infamous for its nearly complete extermination of Guam's native
forest birds. The brown tree snake is a serious threat to the biological diversity of other tropical islands because it can conceal itself in the cargo of ships and aeroplanes, and even in aircraft wheel-wells. It has reached such distant destinations as Micronesia, Hawaii, the mainland U.S.A. and Spain.

The Nile perch was introduced to Lake Victoria in East Africa in the 1950s to counteract the drastic drop in native fish stocks caused by over-fishing. It slowly increased in numbers and then eliminated more than 200 endemic fish species by preying on them and competing for food. The native Lake Victoria fish were no match for the much larger alien perch. The Nile perch's flesh is oilier than that of the local fish, so more trees had to be cut down to fuel fires to dry the catch. The subsequent erosion and run-off
contributed to increased nutrient levels, opening the lake up to invasions by algae and water hyacinth. In turn these invasions led to oxygen depletion in the lake, which resulted in the death of more fish. Commercial exploitation of the Nile perch has displaced men and women from their traditional fishing and processing work. The far-reaching impacts of this alien invasion have been catastrophic for the environment as well as for communities that depend on the lake - but have been quite beneficial for the
export industry from the region.

The beautiful, large purple and violet flowers of the South American water hyacinth make it a very popular ornamental plant for ponds. Notwithstanding, it is one of the worst aquatic weeds in the world. Now
found in 50 countries on five continents, water hyacinth is a very fast-growing plant, with populations known to double in only 12 days.  Infestations of this weed block waterways, interfering with boat traffic,
swimming and fishing. Water hyacinth also prevents sunlight and oxygen from reaching the water column and submerged plants. Its shading and crowding of native aquatic plants dramatically reduces biological diversity in aquatic ecosystems.

The voracious and opportunistic small Indian mongoose is native to Iran through India to the Malay Peninsula. In the late 1800s it was introduced to Fiji, Mauritius, Hawaii and the West Indies to control rats, which themselves had been accidentally introduced and became pests of sugar cane and other crops. Unfortunately, this early attempt at biological control had disastrous effects, among them the extinction of a number of endemic birds, reptiles and amphibians. The mongoose also threatens other
species, such as the rare Japanese Amami rabbit. Worse, the Indian mongoose carries rabies.

"The species in the booklet were selected for their serious impact on biological diversity and/or human activities, and for how they highlight the important issues involved in the alien invasion," says Dr. Mick Clout, a New Zealand professor who heads IUCN's Invasive Species Specialist Group. "Some
particularly notorious cases are listed, but that does not mean that a species absent from the list is any less dangerous. Our purpose in publishing the booklet is to draw attention to the scale and complexity of the rapidly growing invasive species problem. But it is really only the tip of the iceberg. Invading alien species are driving untold numbers of native plant and animal species to extinction worldwide."

Wendy Strahm, the IUCN's Plants Officer, adds that "the effects on biodiversity are immense and often irreversible, and yet awareness of the problem is alarmingly low. The alien invaders are to be found everywhere, among micro-organisms, aquatic and land plants and invertebrates, amphibians, fish, birds, reptiles and mammals. Our scientific knowledge of the world's species is anything but complete but some experts estimate that we are familiar with only 20% of them. In any case, we do not know today
which plant and animal species are useful for the future of humanity, so the protection of biodiversity is obviously essential. So we cannot afford to lose species through the introduction of alien invasives"

"We hope that the publication of the booklet and, recently, of "The Great Reshuffling - Human Dimensions of Invasive Alien Species," a 242-page global study of the subject (edited by Dr McNeely), on the eve of Biodiversity Day, will give it a more prominent place on the agenda of conservationists,
economists and planners, and in the thinking of millions of ordinary citizens."

The list of 100 of the world's worst alien invaders include the grey squirrel, the domestic cat, the Indian myna bird, the Asian longhorned beetle, the sweet potato whitefly, the Asian tiger mosquito, the yellow
Himalayan raspberry, Koster's curse, the starling, Mimosa pigra, the shoebutton ardisia, the red-vented bulbul, the erect pricklypear, and, lastbut not lethargic, the mile-a-minute weed.

For additional information, please contact

Dr Jeffrey McNeely, IUCN-World Conservation Union, Gland, tel 41 22
9990284, email:

Dr Wendy Strahm, IUCN-World Conservation Union, Gland, tel 41 22 9990157,

Dr Mick Clout, University of Auckland, New Zealand, tel 64 9 373599 ext
5281 email: Invasive Species Specialist Group Office
Fax (NZ): 64 9 3737042

Dr Faith Campbell, Washington D.C. tel: 1 202 682 9400 ext 230 email: fax 1 202 682 1331

East African Contact for the IUCN Invasive Species Specialist Group: Dr
Geoffrey Howard, IUCN Eastern Africa Regional Programme, Nairobi, tel. 254 2
890605/12, email

IUCN has a web site on the alien invasive species issue

IUCN Communication contact:
Wendy Goldstein in Switzerland: tel: 41 22 9990282 email
Fax: 41 22 9990025

IUCN - The World Conservation Union was founded in 1948 and brings together
79 states, 112 government agencies, 760 NGOs, 37 affiliates, and some 10,000
scientists and experts from 141 countries in a unique worldwide partnership.
Its mission is to influence, encourage and assist societies throughout the
world to conserve the integrity and diversity of nature and to ensure that
any use of natural resources is equitable and ecologically sustainable.
Within the framework of global conventions IUCN has helped over 75 countries
to prepare and implement national conservation and biodiversity strategies.
IUCN has approximately 1000 staff, most of whom are located in its 42
regional and country offices while 100 work at its Headquarters in Gland,

Saturday 05 May 2001
All (9)
2016 (9)