Web weaving spiders

By Dana Wilde, BDN Staff
Posted Sept. 19, 2010, at 5:57 p.m.

One afternoon, my wife, with her powerful instinct to make things clean, was scrubbing the deck with a high-pressure hose and along the way battering the top of a plastic watering can.
“This hose is taking the paint off the deck,” she said, “but it won’t budge this.”
In the mouth of the can were strands of a cobweb that would not break even under the force of the water. The silk is so tough it can last for years if undisturbed, which is why cobwebs seem to appear wherever you look. In fact, there are all kinds of spider webs practically everywhere. Our deck on summer mornings looks like a construction site, with guy wires strung from house to chair to geranium plant.
These wires are the initial bridges of the familiar spiral-shaped orb webs. To set one up, the orb-weaving spider trails a strand of silk from a prominent spot like a grass tip or a deck chair, and the breeze catches it and tacks it serendipitously to another blade of grass or corner of the house. The spider then walks this bridge back and forth paying out silk to reinforce it. When the bridge feels sturdy and taut, the spider ties another line to it and drops down to secure it below. Next, in a methodical, craftsmanlike process, the spider builds radial spokes and two sets of spirals – one temporary scaffolding, then one permanent — until the day’s web is complete and ready to snare flying meals. A black and yellow garden spider takes a half-hour to an hour to complete the engineering of an orb web 1 to 2 feet in diameter.
I’ve never seen the whole building process from start to finish, but I watched an Araneus diademetus spider ride an orb web fastened between the outside mirror and the door of my car unharmed through 55 mph wind all the way to my house one evening. When we stopped in the dusk light in the garage, the spider fussed with some threads for a minute or two, and then in less than five seconds dismantled the whole thing and retreated under the mirror for the night.
Orb weavers are programmed by instinct — whatever that is — to construct orb webs, while other spiders make cobwebs, sheet webs or funnel webs, which you can see on the lawn covered with dew in the morning. They’re a few inches or a foot wide, and have a funnel in the center where the grass spider, for example, waits for insects to get tangled up, then darts out to capture them. There also are minimalist “reduced webs” that may be only an H shape or even just a single strand.
The silk of an orb-weaving garden spider is about .00012 inch in diameter; at this size, it’s stronger than steel and more difficult to break than rubber. Spider silk can stretch up to 15 percent of its length before it breaks, and in some cases more. This toughness has been compared to Kevlar, which is used in bullet-proof vests and stretches to about 4 percent before breaking. The strongest natural fiber known is the silk of Nephila genus spiders in the South Seas, which islanders make fish nets out of.
You’d think a fiber like this would be manufacturable, but so far no one has been able to figure out how to farm it. To produce the silk in sufficient quantity, you need a lot of spiders, but it turns out you can’t keep too many spiders together in one place because they eat each other.
Spiders’ silk, which is a protein, is produced by glands in their bodies and dispensed through spigots mounted on spinnerets on their abdomens. They spin tiny threads together into single strands, and can generate seven different kinds of silk for different purposes, including insect traps, as well as shelters, egg cases, and nests for mating and in some species nursing their young. Some spiderlings throw out a line of silk from a high place, let the wind take it like a sail, and go “ballooning” off to seek their fortunes in parts unknown. Great clouds of voyaging spiderlings have been reported miles out to sea.
I’ve watched garden spiders carefully making repairs to webs, working the claws at the tips of their legs as dexterously as if they were sewing or knitting. It seems there must be some consciousness of what’s happening in an operation that intricate — the spider clearly makes judgments about strength, tautness, elasticity and shape. Some orb-weaving spiders are more attentive to symmetry and perfection when young, then get a little sloppier as they age. Are spiders aware of what’s functionally necessary and of what’s decorative, or beyond?
How you would ever know the answer to this question, I’m not sure. What spiders think of their silkwork, I do not know, though I’d like to. At least, it’s my instinct to wonder, and I’ve left those cobwebs practically everywhere in one form or another.
naturalist@dwildepress.net

On the Net:
www.spiderzrule.com

http://bangordailynews.com/2010/09/19/living/web-weaving-spiders/ printed on September 23, 2014