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Science: The Clever Arachnids

7 minute read

Spiders, whose ancestors antedated the dinosaurs, have lived on the earth for millions of years. During that time they have picked up a few tricks besides the fly-catching web. There are spiders that look like ants and live with ants; others change color, like chameleons, according to the hue of the flowers on which they wait for prey.

In Australia and Africa there are spiders that catch their victims by a sort of combination lasso and harpoon. They attach a drop of sticky gum to a length of silky thread, and whirl this apparatus around their heads. When something edible approaches, the spider slings the globule. If it hits, it sticks, and the spider reels in the victim—playing it, if necessary, as a human angler does a fish.

These and many more absorbing details of the arachnids’ life are contained in a new book, The Spider, published in England, by John Crompton (author of The Hunting Wasp). Crompton, who describes himself as a layman writing for laymen, writes vividly and with vast enthusiasm. At various times he has been a mounted policeman in Rhodesia, a shipping-firm employee in China, an R.A.F. pilot, a novelist, a beekeeper. He has read—and liberally quotes—the experts, including the great Frenchman J. H. Fabre (TIME, Aug. 22) and several Americans. But his book is larded with personal observations and reminiscences, and he pays his respects to lay enthusiasts like himself: “Our knowledge of spiders—in this country [England] at any rate—is due entirely to spare-time naturalists, men who labour, or laboured, for love; clergymen, schoolmasters, doctors, businessmen and others.”

Temperamental Artist. Not all spiders make prey-catching webs. Of the web-makers, the genus Aranea is the master weaver and engineer. Aranea spins the familiar but complicated “orb web” a large number of segmented rings on a framework of 25 to 35 spokes. Although the typical orb web may have 13,000 or more tie-lines, the spider makes a new web every day, and, like a temperamental artist, never deigns to do repair work. She* puts glue on the silk to make it sticky. To prevent quick drying (or for some other reason), the glue is concentrated in minute droplets spaced along the web strands at regular intervals.

How Aranea manages this was, for a long time, a puzzle to observers. Then says Author Crompton, “the secret came out.” The spider simply twangs the glued tieline, as a bass fiddle player twangs the strings of his instruments. The glue is thus shaken into exactly equidistant droplets.

While building her web, Aranea puts up “scaffolding” (later discarded) to gain a foothold. But, if necessary, she can walk on the glued strands: she has oil on her feet which keeps them from sticking.

When the web is completed, Aranea runs a silken “telephone line” to her nearby lair, and waits for prey. The slightest vibration of the web brings her out on the run. If the victim is a fly or some other small and harmless insect, she drinks its blood on the spot, or paralyzes it with poison from her fangs and takes it to her lair to be kept in storage. If the catch is a big, vigorous, dangerous intruder (a honeybee or a grasshopper), the spider turns her back and squirts out silk in a broad band from all her 600 spinnerets. Only when the victim is trussed up and helpless in silken swathes does Aranea tow it away to the slaughterhouse.

Frightened Cardinal. Not many kinds of spider kill as elegantly as Aranea. One called Agelena makes a heavy sheet web that she spreads out on a bush or hedge, where it looks like a flimsy, dirty handkerchief. Agelena has no glue, and she must subdue her victim before he breaks loose. This involves violent battles and considerable risk every time she tackles something that can fight. But Agelena is a big spider (her body is three-quarters of an inch long), and she has an advantage which one arachnologist has neatly compared to that of a man on skis chasing an enemy who is floundering through deep snow.

House spiders, whose implacable enemy is the housewife, make thick, haphazard webs which Author Crompton regards as a mess. This spider spins only at night, but works indefatigably, and is willing to mend and patch. The only mouse ever recorded as caught and killed by a spider was the victim of a house spider. In Britain, the biggest house spider has a body nearly an inch long, and, counting the legs, is four inches across. This monster is called “the cardinal,” because once, at Hampton Court, one scared the 16th Century’s Cardinal Wolsey almost to death.

Stupid Wolf. Among the arachnids which do not make webs are the “wolf spiders” or hunters, which live in little parapets like watchtowers, from which they leap forth and run down their prey by sheer speed. This group includes the stupid Lycosa, which, when deprived of her cocoon containing young, will accept a cork ball of the same shape and fondle it tenderly. There is also the jumping spider, which stalks her prey like a cat, and pounces when in range. The jumping spider has the best eyesight of all arachnids, with four of her eight eyes on the flattened front of her head.

Unlike bees and ants, spiders do not handle their military and supply problems collectively; they are rugged individuals. Hence it is usually important that the young disperse as soon as possible, in order not to interfere with one another. With most spiders, dispersion is accomplished by ballooning. The young climb in great hordes to an eminence of some sort (e.g., a tree stump), and wait for calm, warm weather. When it comes, the little ones throw out streamers of gauzy silk and rise on warm currents of ascending air. If the currents are spotty, the spiders may come to earth a few yards away, but they may go up to 14,000 feet or higher, travel hundreds and thousands of miles.

Wary Suitor. The male spider has a tough time of it. Except for one type, he is always smaller than the ferocious female, who usually tries to eat him after the mating. She does, too, unless he is quick enough, or clever enough, to get away. One male spider, Pisaura mirabilis, presents his love with a dead fly wrapped in silk, to make her less hungry. Another male, when his mate is in an amorous mood, ropes down her front legs so that when the mating is over she will be unable to chase him.

Moreover, the male spider, having no organ suited to the purpose, fertilizes his partner by artificial insemination. He makes a silk mat, ejects his sperm on it, then dips his palps, or feelers, repeatedly into the sperm. If he survives the preliminaries (females often eat suitors whose courtship is clumsy), he plunges his sperm-laden palps into the female’s belly opening. His duty done, his main concern is to get away alive.

On the whole, Crompton thinks of the spider as a friend of man. Spiders eat enormous quantities of insects, with whom man is waging an age-old war of uncertain outcome. Crompton says that the spiders of England and Wales alone eat 22 trillion insects a year—a harvest weighing more than the human population. He quotes a 19th Century U.S. expert, H. C. McCook, to the effect that man might not be able to survive at all without spiders. Obviously, Crompton deplores the fact that spiders are held in revulsion by many men and nearly all women. Equally obviously, he himself is a fascinated admirer.

* Male spiders are unimportant except for their one task of fertilization. Crompton always refers to a working or hunting spider as “she.”

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