Each country has its own invasive species and rampant plants with a tendency to grow out of control. In most, the techniques for dealing with them are similar - a mixture of powerful chemicals and diggers. But in the US a new weapon has joined the armoury in recent years - the goat.

In a field just outside Washington, Andy, a tall goat with long, floppy ears, nuzzles up to his owner, Brian Knox.

Standing with Andy are another 70 or so goats, some basking in the low winter sun, and others huddled together around bales of hay.

This is holiday time - a chance for the goats to rest and give birth before they start work again in the spring.

Originally bought to be butchered - goat meat is increasingly popular in the US - these animals had a lucky escape when Knox and his business partner discovered they had hidden skills.

"We got to know the goats well and thought, we can't sell them for meat," he says. "So we started using them around this property on some invasive species. It worked really well, and things grew organically from there."

They are now known as the Eco Goats - a herd much in demand for their ability to clear land of invasive species and other nuisance plants up and down America's East Coast.

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