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Everyday Mysteries: Fun Science Facts from the Library of Congress

How do spiders avoid getting tangled in their own webs?

Spiders are able to spin sticky and non-sticky silk. They avoid walking on the sticky silk. In addition, spiders have moveable claws on their feet that grip and release the web’s threads as they walk.

Spiders are invertebrate creatures in the araneae order of the class arachnida in the phylum arthropoda. A spider has up to eight eyes, eight legs and seven silk-producing glands in its abdomen. These glands secrete proteins that are extruded through spinnerets to produce different kinds of silk. Many spiders, particularly orb, funnel, sheet and cob-weaving spiders, use this silk to build webs with which to catch prey.

We’ll focus on orb-weavers because their webs are the most recognizable. Their webs are complex nets of strong dragline threads (frame, spokes) radiating out from the center; and elastic, sticky catching threads spiraling into the center. An orb-weaver begins its web with radial and framework threads using dragline silk, providing a foundation upon which to spiral the sticky catching threads. The spiders then create an auxiliary spiral to help the radial threads support the spider’s weight as it builds. Next, the spider uses, and subsequently destroys, the auxiliary spiral as a guide to create the catching spiral, which it dots with glue. What is perhaps the most amazing part of this hour-long process is that orb-weaving spiders often have poor eyesight and weave using only their sense of touch.

The sticky, complex nets of silk used for the catching spiral are effective hunting tools, but have often made people wonder how the spiders themselves avoid entangling themselves in their own webs. Many people believe that spiders have special oils that repel the stickiness of their threads. This, however, has never been proven. Scientists are still not entirely certain how most spiders manage to avoid ending up ensnared in their own trap, but there are a few accepted theories. Spiders can spin different kinds of silk, and not all of their silk is sticky. In fact, in a spider web only the silk used for the intricate catching spirals are dotted with glue, so spiders know which threads to avoid. In addition to producing different kinds of silk, web-spinning spiders also have an extra set of claws on their feet. All spiders have two claws on their feet; web-spinning ones have three. These claws are used to grasp threads and provide traction as the spider moves along.

Spider silk itself is interesting to scientists because of the irreversible transformation it makes from a water soluble liquid inside the spider, to a non-water soluble thread outside of the body. The reaction has nothing to do with the thread’s exposure to air once it exits the spider; rather scientists believe it has to do with the act of pulling on the thread that realigns the molecules into a solid form.

Scientists are interested in spider silk for manufacturing purposes, specifically the viscid (sticky for catching prey) and dragline (strong for stiff radials and framework) threads. The viscid thread is comparable to rubber in elasticity, but has more strength. The dragline thread is comparable to steel and Kevlar® (bulletproof material) in stiffness, but is more elastic and able to absorb higher impact.

What makes spiders truly unique in their silk-producing abilities is that they are the only animals that use this silk for multiple purposes. Their multiple silk glands each produce different kinds of silk to aid in mating rituals, create shields for protection from predators, encase their eggs and, of course, weave webs.

Related Web Sites

Animal Diversity Web - Site sponsored by the University of Michigan, Department of Zoology covers information about many animal species, including general information, natural history, classification and images.
How Stuff Works - Section of a larger article on spiders describing web spinning behavior.
“New” spider species weaves uncommonly regular webs - Article on National Geographic website about a new species of spider; also goes into some detail about web-weaving activities of spiders in general.
The Spider Myths site - Web site hosted by the Burke Museum of Natural History and Culture at University of Washington refuting the urban legend that spiders avoid entangling themselves in spider webs because of oils on their feet. Find other misconceptions about spiders from the Spider Myths home page.
Spider sense: fast facts on extreme arachnids - Article on National Geographic website detailing fun facts about spiders.