ASK A SCIENTIST
Question: How come some spiders with spinnerets they don't spin webs?
Many will disagree, but spiders are absolutely amazing, interesting, beautiful, beneficial creatures. So far, scientists have identified 41,253 species of spiders in the world, which may be just a fraction of the actual number that exist. Contrary to our intuition, the majority of spider species don't actually make orb-webs. Yet, all spiders have spinnerets and are capable of producing different types of silk.
Spider silk is made up of special proteins and is a remarkable material that, relative to its density and weight, has a tensile strength greater than steal, is rot and temperature resistant, and is highly ductile (stretchable). One of the most common uses of spider silk is called a dragline. One of the strongest types of silk, a dragline is basically a safety line in case a spider needs to drop off a branch to evade being eaten or gets pushed or blown off its path. It's a natural bungee cord. Baby spiders, or spiderlings, will utilize dragline silk to float away in the wind (ballooning) to disperse to new areas. Other common applications of silk are to wrap up prey and to build protective egg sacs.
Some spider species wield their silk as 'weapons' to capture prey. The Net-casting spider hangs upside down capturing insects in a silken net held by four of its legs. Another weapon making spider is the Bolas spider which creates a ball of glue on the end of a silk line similar to its namesake to capture moths.
Many spiders use silk to alter, strengthen, or make homes other than webs. Many spiders line their burrows with silk lines to detect vibrations of meals or intruders. Trapdoor spiders make their doors out of silk. Some spider species use their silk to roll leaves for shelter. The Diving-bell spider of Africa, Europe, and Asia creates its own silken underwater air tank.
It's unfortunate that spiders inspire so much trepidation in people as there are so many different cool species as evidenced just by their many uses of silk, and they are highly beneficial to us. Spiders are a non-chemical insect population control. Silk is being researched to help make lightweight strong materials for humans. Some people in Indonesia employ spider silk as fishing line. Most spiders are harmless and would justifiably rather hide from humans than be on the losing end of an encounter with us. But, if we take a moment to observe a spider, we may see one its fascinating applications of silk.
Ask a Scientist appears Thursdays. Questions are answered by faculty at Binghamton University. Teachers in the greater Binghamton area who wish to participate in the program are asked to write to Ask A Scientist, c/o Binghamton University, Office of Communications and Marketing, PO Box 6000, Binghamton, NY 13902-6000 or e-mail email@example.com. Check out the Ask a Scientist Web site at askascientist.binghamton.edu. To submit a question, download the submission form(.pdf, 460kb).