These "invasive alien species" are one of the primary threats to biodiversity and the risks, especially to isolated ecosystems such as small islands, are likely to grow due to booming global trade, transport and tourism, the experts say.

Introduced to the southern United States in the early 20th century, the RIFA ants have stowed away in a range of imported goods and containers and are now found in Asian and Pacific countries, including China, Taiwan, Malaysia and Australia.

More aggressive than most other ants, the RIFAs give workers painful bites which turn into fluid-filled blisters, scare off animals which protect crops from insects and gnaw through wires on equipment causing between $500 million and several billion a year in the United States alone, say UN experts.

The Bonn biodiversity meeting is studying how to tackle creatures like the RIFA ants which are inadvertently moved from their natural habitat by global trade and then wreak havoc on the environment.

"The problem is enormous -- far bigger than people had previously thought," Sarah Simons, Executive Director of the Global Invasive Species Programme (GISP) told Reuters.

ECONOMIC COST

Other examples include cactus moths, which destroy prickly pear cactuses. Scientists have warned the moths could wipe out cactus in Mexico where their pads are grown as crops for food.

In the Bahamas, invasions of lionfish are devouring other fish and tree snakes from Guam are threatening birds in Hawaii.

GISP's website cites a US study which puts the global damage from invasive alien species at $1.5 trillion but Simons says more robust research is needed to convince people of the scale of the threat.

She advocates better quarantine arrangements as well as better insurance and liability mechanisms. Other measures can include tighter controls of air cargo or ships' ballast tanks.

UN experts say the Asia-Pacific region could offer lessons having curbed the spread of RIFAs by the monitoring of populations and installation of early warning systems.

"If we apply the precautionary approach, the spread of alien species can be limited," said Junko Shimura, the Convention's Programme Officer for Taxonomy and Invasive Alien species.

Preventing the international movement of potentially invasive living organisms and rapid detection at borders is cheaper than control and eradication, which sometimes require environmentally damaging pesticides, she said.