"Nature Guide Journal"

6 September 2001

(Updated 23 August 2002)

Last weekend, our two young guests and daughter watched as the garden spider gently pulled herself out of her old skin. Dangling from the underside of a swollen rose hip, the spider eased legs-last out of her now-too-small, striped skin.

Like other arthropods, including crabs and insects, spiders must shed or molt their hard, jointed exoskeleton in order to grow larger.

Although often misnamed insects, spiders are actually quite different. Most notably, insects have three body-parts, six legs, and two compound (many-faceted) eyes; spiders have two body-parts, eight legs, and (generally) eight simple eyes. And, instead of the usual insect antennae, spiders have short, leg-like appendages ("pedipalps") between the first set of legs and the fangs.

Pedipalps can be used to distinguish between spider sexes: fertile adult males have swollen pedipalps; females and immature males have slender pedipalps. In some species of wolf and jumping spiders, the pedipalps of fertile males are showy or brightly colored and used in courtship display.

While many insects produce silk, spider silk is stronger and more versatile. Stronger than steel the same diameter, there are several different kinds of spider silk.

While not all spiders produce all kinds of spider silk, most produce a variety of silk for a variety of uses. Spiders use silk to snare their prey, camouflage themselves while awaiting prey, subdue prey, and wrap it for storage. Spider silk is also used in transportation: as trails or rappel lines or air balloons. Spiders use silk to build dens and egg cases, and some water-dwelling spiders even use silk to construct diving bells to hold air under water.

Some male spiders use silk in the process of impregnating females. Male spiders produce sperm in a gland on the underside of their abdomen—a rather inconvenient location. The male uses his pedipalps to drain off (sometimes employing special webbing) and hold the sperm until mating, giving masculine pedipalps their swollen appearance. The males of some spider species wave and flaunt their sperm-filled pedipalps during courtship before reaching under the female to deposit the sperm.

And, no, the females don't always eat their mates, though the males do usually die shortly after mating.

Some medical authorities state that most "spider bites" are actually made by other arthropods, usually insects. Two species of poisonous spiders are found in Oregon--though rarely encountered: the western black widow (Latrodectus hesperus), and the hobo spider (Tegenaria agrestis).

Not native to Oregon, the few brown recluse spiders (Loxosceles reclusa) found here are usually traced to household goods that were brought in from other regions.  

All spiders are predators that inject their victims with tissue-dissolving venom, but virtually all their victims are insects and other very small animals. Catching, dissolving, and literally sucking the life out of insects make spiders an important top predator.

Oregon has many beautiful and fascinating spiders, from well-known garden orb-weavers, to brightly-marked jumping spiders, to yellow crab spiders hiding in flowers.

Hikers enjoying our warm fall frequently encounter big spiders on large webs stretched across the trail—trails that seemed to have no webs earlier in the summer. Watching our garden spider become noticeably bigger than her cast-off skin made it clear that these intriguing animals do become suddenly larger in autumn.

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Check out Ed Nieuwenhuys' website for more detail on spider silk–including photomicrographs of spinnerets. 

Also,  Bill Amos has an informative personal site on spiders.

Detailed information on the poisonous hobo spider is listed on the Darwin Vest site.