Welcome to You Ask Andy

Kathryn Straple, age 9, of Seattle, Wash, for her question:

Does a spider fly from twig to twig?

We sometimes tend to forget it, but the busy little spider is one of our most reliable friends. She is by nature a hunter, a trapper. And the game she hunts is insects, the pesky flies and moths that trespass upon our share of the world.

The spider family is a big one and various cousins live wherever insects are to be found. Altogether there are almost 30,000 of them over 2,000 of the cousins enjoy life in North America. Not all spiders spin webs, but all of them spin silk for some purpose. Some spin silk to line their burrows and some spin silk only to make a soft cocoon for their babies.

Many spiders live on the ground and stalk their prey on food. These predatory fellows hunt the little beetles and bugs who skittle among thickets of grass. These spiders are strong, but they are not acrobats. The aerial acrobats of the spider world are the web spinners and certain tree spiders. We have all admired those gauzy webs, tile have all wondered how they string the silken cables from twig to twig. And some of us have been astonished to see a fat little wingless spider gliding through the air ‑ or so it seems.

Actually, that acrobatic little spider is very firmly anchored at all times. She is hanging at the end of a gauzy cable of fine strong silk. She swings to and fro on the breath of a light breeze.

A tree dwelling spider uses those acrobatics all the time. She is merely moving from bough to bough in search of food. She may or may not be a web spinner. A web spinning spider does a few aerial acrobatics when she fixes the main cables to form the framework of her web.

The silk is spun from spinnerets where the spider's tail would be. The substance is almost too fine for your eyes to see. At first the silk is a gooey substance and the spider fixes one end firmly to a twig. The silk soon dries into a firm thread and the little acrobat is already to go.

She plays out a line of silk. It dries and lifts on the breeze. Pretty soon the lift is strong enough to bear aloft the little spider. Off she floats into the wide blue yonder. But not for long. She may enjoy the swing through empty space, but she knows just where she is going. And she keeps her mind on her work.

She selects a twig some distance from the first. As she swings by, she grubs. Behind her is a cable of silk stretching from the first twig. The little acrobat now has a tightrope, a cable across the space between two suitable twigs. She makes a second end of her cable fast and goes on to build other cross beams.

The tree spider who does not build a web may run up and down her air borne cable. Or she may cross it in tight rope fashion. The web builder has more work to do. When her cross beams are finished, she goes to the center. She now spins a finer silk, working in a spiral. From time to time she stops to place a little glue on this spiral thread. This will trap a pesky fly ‑ but not the wild spider. She trips gaily over her web, being vary careful to step only on the cross cables which have no glue.

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