This question comes up every autumn, so it’s apparently worth the revisit.
They seem to appear overnight: spider webs stretched over paths and trails where there were none before -- often with huge spiders poised upside down in the center.
Most conspicuous webs people notice are “orb” webs, the stereotype classic spider-web shape that span open spaces. Only two groups of spiders weave orb webs; Oregon has a couple of native species and at least one introduced species of orb web weavers.
Up to five times stronger than steel, spider silk is a water-proof protein. The silk is extruded as a liquid through four to seven nozzle-like spinnerets at the far end of the spider’s abdomen. Each spinneret produces one of several kinds of silk and the silk production is adjusted by the spider for different uses.
As the liquid silk is extruded, it polymerizes (small molecules join to make giant molecules) and hardens in the air while being stretched taut by the spider. The spider pulls and handles the silk using comb-like claws at the ends of its legs.
The raw material for spider silk production may include yesterday’s silk: web-weaving spiders often eat the old webs along with the caught prey and often eat webs that need repair or replacing, sometimes recycling the web daily.
The beautifully intricate orb webs -- a classic Halloween design -- incorporate several different kinds of silk laid out in a specific pattern. The orb weaver begins with the outlining framework (the “foundation”) that’s filled in by spokes. A central hub is held secure by a spiral of silk and then more silk is spiraled out toward the edge of the web’s foundation. At least part of these structural spirals is then replaced by sticky silk. Sometimes a “free zone” is left without sticky strands.
Why don’t spiders get caught in their own webs? They simply don’t step on the sticky strands.
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Only the orb web-weavers produce a sticky silk. Other web-building spiders rely on a tangle of silk to trap their prey; still others forego traps and actively hunt down their dinner, though they still make silk for other uses.
While not all spiders produce all kinds of silk, most produce a variety of silk for uses far beyond prey snaring. Spiders use their silk -- often a specific kind -- to wrap and store prey, build or line burrow, protect egg masses, camouflage eggs or homes, send aloft as balloons for air travel (especially very young spiders), make a storage/transfer site for semen, or use as draglines for recovering from a fall. Spider silk also can be used for rappelling and climbing or finding their way home. Some water-dwelling spiders even use silk to construct diving bells to hold air under water.
Other animals sometimes use spider webs, too: hummingbirds, for example, use spider webs in nest building.
The components and configuration of a spider’s silk creations may be unique to each species. In fact, some spiders can be identified by the size, shape, and location of their webs. And, of course, the relative size of a particular web is also determined by the size of the spider that spins it.
Like other arthropods, including crabs and insects, spiders must shed or molt their hard, jointed exoskeleton in order to grow larger. There’s a new skeleton beneath the old. Once the old exoskeleton is off, they’ll inflate the soft new skeleton before it hardens, becoming significantly larger in minutes. They’ll stay the new size until they molt again.
Huge spider webs suddenly span trails and walkways in autumn because their creators finally grow large enough with the summer’s last molt to accomplish the engineering.