Spiders make their silk naturally as a water-soluble protein which they then force through a tiny hole in their bodies, spinning it out as a thread.

Nexia scientists put spider genes in mammal cells to make their version of the silk. The company now has genetically modified goats that will produce the protein in their milk.

Military interest

Spider silk has the perfect qualities for making products like body armour, medical sutures and biodegradable fishing lines. The problem for science has been finding a way to produce it in industrial quantities.

The US army has been interested in the substance since the 1960s, after substantial numbers of soldiers were killed in Vietnam by high-velocity bullets.

Only heavy, cumbersome, body armour offers any protection at all against such bullets, and the army discovered spider silk would be an ideal material for making lighter, tougher armour.

"People said 'Why don't we farm them like we do with gregarious vegetarian silkworms?'," said Dr Turner. "But spiders are territorial carnivores. They just aren't suited to farming."

"Put 10,000 of them in a room and a week later you'd have one mean-looking one left."

The US Army and the Canadian Department of National Defense worked together with Nexia on the spider silk project.

Gene transplants

Scientists have for years been putting spider genes into various more-friendly organisms to try to get them to produce the precious silk.

Dr Turner said other companies drew a blank when they tried yeast and bacteria, or ended up with silks that were not spinable or strong enough.

In the end, Nexia's scientists succeeded with the aid of laboratory cells originally taken from cows and hamsters. Dr Turner said that they had set out to prove that copying nature was possible and had ended up completing the whole process of synthesising spider silk.

"We've taken spider genes... we've made authentic water-soluble proteins. We've done what the spider does and dehydrated them and pushed them out through a tiny hole."

The researchers now want to make larger quantities of their silk using milk from a herd of goats carrying the spider genes. These genetically modified animals have been bred from a pair that made their first public appearance in August 2000.

The daughters of the original pair are now pregnant with their own offspring and Dr Turner hopes the enlarged herd will soon be helping Nexia turn out useable quantities of spider silk yarn.

Nexia's research is published in the journal Science.