Extreme Ecology On Christmas Island

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Australia's remote Christmas Island is home to 1700 people and one hundred and fifty million red crabs, peacefully coexisting. Then came exotic yellow crazy ants, which scientifically preyed on the crabs. (How did they learn to do that?) It was a minor problem until the further arrival of scale insects. Feeding on plants, these produce a nutritious liquid called honeydew. The ants learned to farm the scale insects, boosting their strength so much they formed gigantic colonies. They could spray so much formic acid into the air that it became a chemical weapon. Clouds of it wiped out crabs en masse, whereupon the ants occupied their abandoned burrows to raise more ants. The colonies grew so large they threatened to wipe out all other animal species.

The people didn't like that. They tried ant poison, no luck. Next they introduced a tiny wasp that preys exclusively on scale insects. That turned the tide.

 
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Many island countries face these issues. In New Zealand, biosecurity is strict: travelers declare risky goods, including food, plants, seeds, wood, flowers, animal products, outdoor gear, herbal meds, and natural products. Bags are x-rayed, searches are conducted, and sniffer dogs check travelers.

Some declared items may be allowed, but others, like fresh fruit, meat and dairy products, seeds and untreated plant material, will be confiscated to protect NZ from pests and diseases.

They would check your boots and ask where you've been in the past few weeks, like on a farm or some related ground where pests and diseases might follow you to NZ.
 
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Hornbein said:
They tried ant poison, no luck
The poison was effective in eliminating supercolonies of the ants where applied, but not effective in the elimination of all ants on the island. Species specific poisons are rare, if non-existent, Cross-over poisoning of other species susceptible to the poison would also occur. For this case, a broad application across the whole island as a means to eliminate the 'ant' problem was ruled out, as that would also have eliminated the species needing 'protection' ( the red crabs ), and others. Local application of the poison in targeted supercolonies was 100% effective, but only shorterm as a solution.

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Funny thing is that most people would consider the Ant-invaded forests as being more desirable than the Uninvaded forest, just because the look is more green - the Uninvaded forest brown look is NOT that of a dying ecosystem. Far from it.

https://www.dcceew.gov.au/sites/def...brochure-detail-crazy-ant-control-options.pdf

Species that have invaded North America in recent years ( after discovery )are ( locally or more generally across the continent ) through either directed by humans for supposed economic reasons ( agricultural , horticulture, pet industry ), or hitching a ride on transport vehicles.
house mouse, rats, cats, dogs, horses, cows, chickens, sheep, wild boar, squirrel, pigeon, sparrow, python, goldfish, pickeral, mussels, snails, grasses, trees and other vegetation.

Full list\ species specific:
https://en.wikipedia.org/wiki/List_of_invasive_species_in_North_America