Scientists have discovered how metal-munching earthworms can help plants to clean up contaminated soils.

By Elizabeth Mitchell
Science reporter, BBC News

Worms munching polluted and non-polluted soils showed different colours

Researchers at Reading University found that subtle changes occurred in metals as worms ingested and excreted soil.

These changes make it easier for plants to take up potentially toxic metals from contaminated land.

Earthworms could be the future "21st Century eco-warriors", scientists suggested at the British Association Science Festival in Liverpool.

There are many sites across the UK with contaminated soil due to previous industrial activities, including mines, engineering works and lead smelters.

The dream scenario is that the plants become so efficient at extracting the metals that you can take them off to a smelting plant Mark Hodson

Earthworms are ideal "soil detectives": their presence can act as a reliable indicator to the general health of the soil.

They have evolved a mechanism that allows them to survive in soils contaminated with toxic metals including arsenic, lead, copper and zinc.

"Earthworms produce metallothinein - a protein that is specifically designed to wrap around particular metals and keep them safe," explained Mark Hodson from the University of Reading.

"In broad terms, if an earthworm can cope with one type of metal, it can often cope with a suite of metals," he added.

An extremely rare female frog has been spotted for the first time in 20 years.

The tiny tree frog, Isthmohyla rivularis, was seen in Costa Rica's Monteverde Cloud Forest Preserve.

This species was thought to have become extinct two decades ago, but last year a University of Manchester researcher caught a glimpse of a male.

However, the discovery of the female and more males suggests this species is breeding and has been able to survive where many other frogs have not.

Andrew Gray, a herpetologist from Manchester Museum at the University of Manchester, said: "This has been the highlight of the whole of my career.

The only time you ever come across a female is by chance Andrew Gray

"Now that we know that both sexes exist in the wild, we should intensify efforts to understand their ecology and further their conservation."

The BBC has been following the team from the University of Manchester and Chester Zoo that is working on amphibian conservation programmes

The BBC video of the frog is the first-known footage of this species.

The 2.5cm-long female, which was released after the discovery, was brown with metallic green speckles and was packed full of eggs.

A difficult task

Finding female frogs is extremely difficult; males make a distinctive call but females are silent for most of the time.

And tracking down this particular species in a great expanse of rainforest was even more difficult - the team had few clues about where the frogs might be, and the search could only take place at night.

The team trekked deep into the forest to a spot close to where the male Isthmohyla rivularis was spotted last year.

The researchers first discovered another male from its soft insect-like call.

The conservationists then trained their torches on the undergrowth, and eventually Luis Obando, head of park maintenance at Monteverde's Tropical Science Center, found the tiny female, which was sitting on a leaf.

Mr Gray told the BBC: "It is hard to describe just how unlikely it was to have discovered a female of this particular species.

"The only time you ever come across a female is by chance - and it is only once in a blue moon that they come down to lay their eggs. You really have to be in the right place at the right time.

"You could come out here every night for a year and not see a thing.

"I really think that this time we have had luck on our side."