By Richard Black BBC science correspondent

Scientists in Japan have genetically engineered silkworms to produce the substance collagen, which is widely used in cosmetic surgery.

They say that GM silkworms are an ideal way to manufacture a wide range of materials for use in medicine, including perhaps ways of reducing the risk of HIV infection.

Scientists at Hiroshima University inserted human collagen genes into the DNA of silkworm eggs.

In due time, the eggs hatched and the worms began spinning their cocoons - but these cocoons included not just silk, but collagen, too.

Commercially viable?

Collagen is widely used in cosmetic surgery to re-construct damaged flesh.

At present, most collagen comes from cows, but the Hiroshima researchers have calculated that making human collagen from silkworms would be commercially viable.

They could also potentially produce many other useful things, too.

Some researchers are developing GM silkworms to make drugs for thinning the blood; other scientists believe they could produce substances able to reduce the risk of HIV infection.

In many countries researchers are developing genetically modified farm animals such as sheep to make the drugs of the future.

But in many Asian countries such as Japan, where there is a tradition of silk production and limited space for keeping animals, the humble silkworm could be a better option.