Silk from other animals

The main ingredient in spider silk is proteins, and there are many different kinds, depending on which spider is spinning and which silk it wants to make. Some of the proteins are very large and complicated, and therefore hard to make a lot of, in the lab.

Some scientists have put the genes(units inside cells) that have the instructions for making silk into other creatures, such as goats. Some of these special silk-making goats live at the University of Wyoming.

The silk-making genes are turned on only in the goat cells that make milk, so when these goats are milked, there is silk in the milk. Right now, it is hard to get a lot of silk in the milk. A liter of milk may have only 15 grams of silk, which means it would take about 600 gallons of milk to make one bulletproof vest. At higher concentrations the milk starts clumping, perhaps because the silk proteins are sticking to milk proteins, scientist says.

Tara Sutherland, of Australia's Commonwealth Scientific and Industrial Research Organization in Canberra, is focusing on silks made by insects other than silkworms. Many insects make silk, although only one kind each. Sutherland has zeroed in on the silks of bees, wasps and ants.

"Imagine a hive and each new generation of bees being wrapped in a silken cocoon," she says. "If you remove the wax and look where the bees were raised there is silk "beautiful sheets of golden silk." The bee silk probably protects the baby bees in the hive, says Sutherland. Bee silk might also add structural support to the hive and prevent the wax from getting so warm that it melts. Sutherland is also investigating weaver ants, which use silk to stitch leaves into nests. It seems only the baby weaver ants make silk.

The adults hold the little larval silk-makers, moving them around for desired silk placement. The silks made by stinging insects such as bees have a different structure from other silks.

It looks like spiraled pasta versus flat sheets of linguini, says Sutherland. And bee and ant silk is both tougher and more stable than silkworm silk, she says. Though nothing beats spider silk, because bee silk is made of simpler proteins, it might be easier for scientists to make in the large amounts needed to create everyday things for humans.

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Fact file on spiders

* Spiders are one of the oldest groups of animals on the planet.

* Scientists have found fossils of spiders that are 380 million years old.

* Spiders are a very diverse group; more than 37,500 species of spider have been described (consider that there are only about 10,000 kinds of birds).

* Most spiders have an abdoman made up of five different sections. The last two sections are where the silk-making happens. These sections of the lower belly are modified into special structures called spinnerets, which are sort of like faucets for silk. The silk is mixed in glands and then secreted out of the spinnerets

* They attach the emerging silk to something, like a tree branch, and then move away from the branch. This pulls the silk outward.

* One spider usually has several different glands and spinnerets for making several different kinds of silk. In their webs, most spiders use dragline silk for the outer rim and spokes. Strong as steel, dragline silk is also used as a safety line when a spider falls from a high shelf or branch.

* For the inner part of the web, where an insect such as a buzzing fly might get caught, spiders use an extra sticky silk.

* They wrap these freshly caught snacks in another silk, called aciniform silk.

* Spiders use another silk, one that is very stiff, to wrap and protect their eggs. Even spiders that don't make proper webs make silk.

* Scientists recently discovered that tarantulas, which use burrows instead of webs as homes, make silk from spigots on the end of their feet!

* The most studied spider silks come from the golden silk spider, Nephila clavipes, and the European garden spider, Araneus diadematus.

* Scientists have made ultrathin films out of dragline silk that in the future might be used as bandages for dressing wounds.

* Spider silk is also being used to make porous, or holey, gels and sponges. When placed in these sponges, tissue, bone and nerve cells are held steady while they grow. These silk sponges will fall apart or degrade gradually, after the cells have been given enough time to grow.

- Science News

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