Predatory spiders spin silk into cocoons and webs to catch their prey, while silkworms only use their silk for cocoons. These two very different species produce strong, versatile, elastic and lightweight fibers. Both kinds of silk have a myriad potential uses in military and medical fields. The differences between spider silk and worm silk have inspired scientific research into these animal-produced threads.
Differences in Thickness
Differences in the thicknesses of these two kinds of silk threads are inversely proportional to their strengths. Worms make silk of a consistent thickness, while spiders produce several types of silk with varying thicknesses. Silk worm thread is 10 times thicker than spider silk, measuring an average of 0.03 inch in diameter. Spider silk measurements vary from 0.00012 to 0.00032 inches in diameter. Spiders use valves in their necks to regulate the thickness of silk.
Differences in Strength
Although both types of silk are extremely light and strong for their size and thickness, spider silk is much stronger than worm silk. Scientists estimate spider silk is at least twice as strong as the type made by silkworms. Spider silk is extremely elastic and stronger than Kevlar and steel, neither of which stretch at all. Factors accounting for the varying scientific opinion about the strength of spider silk are easily explained. When spider silk absorbs water, it becomes less brittle and more elastic. Measurements taken at different levels of humidity account for the differing results.
Differences in Production
Differences in the production of spider and worm silk range from physical techniques to economic and even animal-rights issues. Worm silk is produced by the caterpillars of silk moths (Bombyx mori), whose eggs hatch into larvae that each spin one mile of continuous silk thread into cocoons. Silk farmers heat these cocoons to kill the silkworms and harvest thin threads. Spiders release silk from abdominal glands. A 11-foot length of silk cloth made by over 1 million wild golden orb spiders from Madagascar took 70 workers four years to make. This time includes collection of the spiders, who were fed crickets, not harmed during the harvesting and later released. Commercial production of spider silk is difficult because spiders produce very little silk at a time, and these territorial creatures cannot live together without killing each other. Animal-rights activists object to this production process.
Differences Affecting Medical Use
Super-strong silk threads are very useful in medicine. Surgeons can make superior sutures with this material; burn patients of the future may be spared painful skin grafts, all due to the properties of these silks. Worm silk causes a reaction from the human immune system that makes it less suitable for these purposes; it has been suspected of causing asthma attacks in sensitive patients. Spider silk does not have this drawback. Spider silk cannot yet be produced in quantity in test tubes. Current experiments involving genetically altered plants and animals are attempting to produce enough silk thread for medical uses.