spider silk origin

Asked April 12, 2017, 7:25 PM EDT

dear sirs,
i have always been fascinated by spider silk. one pound would circle the earth. i understand that they are splicing spider genes into silk-worms to produce a product combining the best of both species, and now it can be mass-produced and harvested. however something has always bothered me-
if spiders are arachnids and the worms are insects, then why is it that they both produce '"silk"?
did they inherit some protein from a pre-cambrian ancestor and independently develop it? are they only super-ficially similar and the researchers are making an "alloy" of them?
thank you, BA

Klamath County Oregon entomology

1 Response

Many different insects and all spiders produce silks. The best evidence suggests that silk production evolved independently in arachnids (spiders and mites) and insects. Within the insects, silk production may have evolved independently a number of times. Each species of insect that produces silk produces a single type of silk. Some produce silk for reproductive purposes (the egg stalks of lacewings), others produce it for protection (webworm nests in trees, cocoons), and others for attachment (black fly larvae in streams). However, every spider species can produce many different types of silk (a single species may produce 8 or 9 different silks) – for different purposes and with different chemical compositions and physical properties.

The type of spider silk material scientists are most interested in is dragline silk. This is the silk used for the frame of webs and is the silk spiders use as a parachute when they have to make a quick escape. Dragline silk has tremendous tensile strength, which weight for weight makes it stronger than steel or other hard materials. The fibers are also have a much smaller diameter than synthetic fibers. So who knows what could be made if we just could get enough of it!

That’s where the silkworms come in. It’s a lot easier to rear large numbers of silkworm caterpillars than spiders. People have been doing that for thousands of years by feeding silkworms mulberry leaves. So, the thought has been to insert genes for spider silk into the silkworm, and it has been done with some success. However so far, the modified silkworms produce both their own silk plus the spider silk (so it’s an alloy, in that sense). Both silks are valuable, obviously, but it would be ideal to have silkworms that produced one or the other – not mixtures. So there are still some bugs in the process.