NZ snail leaves trail of destruction across US

New Zealand mudsnails - regarded in the United States as a tiny pest with a voracious appetite - appear to have invaded the trout rivers of Colorado, the Denver Post reports.

State wildlife officials expect more discoveries of the species in popular fly-fishing rivers after an off-duty biologist found some in the South Platte River in Elevenmile Canyon.

The mudsnail is making a slow-motion invasion of the American West: late last year it was confirmed in Colorado in Boulder Creek, just northeast of Boulder city. Scientists were surprised because until then the nearest known population of mudsnails was in northeast Utah.

The tiny (up to 5mm) mudsnails, native to New Zealand, were originally discovered in Idaho's Snake River in 1987. Americans claim the species is capable of stripping entire river systems of their algae, starving their native caddis and stone flies, the basic food supply for trout. More than 750,000 can live in a square metre.

The snail can clone itself, reproducing at remarkable rates. In two years, according to the Washington State Council, a single mudsnail can produce a population of 3.7 million. It can travel long distances in uncomfortable conditions, tolerates weeks of dry weather, and is not fussy about its diet.

Colorado state wildlife spokesman Pete Walker said the species had no natural predators in the US.

"They are almost aggressive in the way they motor around and seek new things. If you are walking around in a stream, these snails are going to be checking out your feet. And if you stand in one place very long, some of them are going to come onboard."

Anglers were asked to soak their boots or waders in a diluted solution of a household cleaner, which seemed to make the mudsnails release their grip.

- NZPA