From orb-webs to pallets, spiders try their best in Southeast Alaska

Posted: Sunday, April 13, 2008

The most common responses to seeing a spider are fear and loathing, accompanied by a shrill EEEEK and a smack.

Spiders are the stuff of numerous horror movies and spooky Halloween tricks. But this is a bad rap!

All spiders are predators and almost all spiders are venomous (there is a small group that is not). Their venom is an adaptation for subduing their prey, which is usually an insect, but very large spiders may take small vertebrates too. There are hundreds of species of spider in Alaska, but most of them pose little or no risk to us.

Spiders catch their prey in a variety of ways. There are spiders that chase down their prey and others that ambush their victims. Crab spiders lurk in flowers, generally mimicking the color of the flower, and snatch unwitting flower-visiting insects (including pollinators). Other, such as the web-builders, build traps.

The spiders we usually notice are the ones that build webs. There are many kinds of web-builders and many styles of web. The common house spider builds messy webs in nooks and corners. In the early morning one might see dozens of "bowl-and-doily" webs, glistening with dew, scattered in bushes and grasses; the tiny builder is usually concealed under part of the web.

The most conspicuous and familiar webs belong to the to the orb-weavers. These build the elegant silken webs we sometimes see stretched across a trail or between bushes. These orb-webs are traps for catching flying insects. The basic construction of a typical orb-web is a spiral of sticky silk supported by radiating, non-sticky but stretchy "spokes" that attach the trap to the surrounding vegetation. The orb spider commonly sits at the edge of the web, with one leg touching a strand. When a bug flies into the trap and shakes the web, the spider then rushes out and subdues its prey. The spider typically wraps up the prey in a skein of silk before retiring to eat it.

Most orb weavers take down their web and eat it when night is over, thus recycling the protein of the silk to be used in making a new web the next night. But some species leave the web in position and repair it if it gets torn. These spiders typically make their webs conspicuous, by using colored silk or by constructing a patch of white silk in the middle of the web. This so-called stabilimentum has nothing to do with stability (contrary to its name). Its main function seems to be making the web conspicuous so that birds don't fly through it and wreck it: Where there are no birds, the spiders stop making stabilimenta.

Some potential prey insects seldom get caught in sticky webs. Moths, for example, flutter vigorously when they blunder into a web and bounce out or slide to the edge of the web. The colored scales on the moth's wings stick to the web and detach from the wing, so the moth itself is free to fly away. Similarly, caddisfly adults have detachable hairs on their wings and allow the caddisfly to escape the sticky web.

Some insects, including stinkbugs, spray noxious chemicals when attacked by a predator. Certain spiders bite their prey before wrapping it up in silk and thus get sprayed by the deterrent chemical. Other spiders can deal with this problem by wrapping the prey in silk before biting it and injecting venom. If a stinkbug manages to emit its nasty discharge before getting wrapped up, the attacking spider reacts violently - running rapidly away and energetically cleaning itself. Meanwhile the clever stinkbug spits on the places where the sticky web is in contact with its body or legs. The saliva dilutes the stickiness and makes the strands stiff instead of stretchy. The web is then breakable and the bug can often extricate itself and fly away.

Ambush bugs are small, venomous, predatory insects that sometimes get caught in orb webs. When the hungry spider approaches, the ambush bug injects its venom into a leg of the spider. The usual reaction of the spider is to pinch off its own leg. The ambush bug's venom is lethal and the spider saves its life by giving up a leg: a counter-defense to the defense of the prey.

People always worry about getting bitten by a spider.

Here in Southeast, there are not many spiders that are likely to hurt us with their venom. Most native spiders here are too small and their jaws are too weak to penetrate human skin. A few native species are large enough to inject venom into humans and may also induce an allergic reaction in some people.

But the majority of spiders that are likely to cause slow-healing wounds from injection of venom are outsiders, coming here from elsewhere. Famous nasty spiders such as the brown recluse and black widow may come to Southeast in freight, such as carpet and furniture. However, they apparently cannot establish populations here, except temporarily in basements and junk piles.

Another unpleasant exotic is the hobo spider (and its relatives), which likes to nest in wooden pallets and can come in with freight. So far, however, the hobo does not seem to be established here. One of the hobo's relatives is established in Wrangell, and possibly in Juneau. We also have the false black widow, lacking the red hourglass figure on the underside of the abdomen. This species is said to be about as nasty as the black widow but less aggressive.

In any case, if you see a spider, it is likely to be harmless to you and useful in eating various insects.

If you are bitten, and if there is a question about what spider it is, the best plan is to catch it gently and take it to an expert for identification. EEEEK and smash are much less edifying, because a smashed spider cannot be identified and proper treatment is made more difficult.

• Mary F. Willson is a retired professor of ecology and a Trail Mix board member.



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