Because the outstretched cordage may warn them of the temporary entanglement of their prey, on which they instantly rush, and devour, after the infliction of a mortal wound. Many lie in wait beneath leaves, and others spin comfortable tunnels, or watch-towers, as they may be called, in which they repose till the vibration of their nets below calls them into active service.
Because they trust to strength, activity, and cunning, for their daily, or, it may be, monthly fare; for spiders, though voracious in times of abundance, are capable of frequent and long-continued abstinence.
Vaillant had a spider that lived nearly a year without food, and was so far from being weakened by abstinence, that it immediately killed another large spider, equally vigorous, but not so hungry, that was put in along with it. Baker is known to have kept a beetle in a state of total abstinence for three years: it afterwards made its escape.
Several of this webless species leap, and others hunt down their insect food by speed of foot, and a few on the surface of water. A large species, common in Norfolk, constructs a raft of weeds, or floating island, on which it is wafted about, and from it seizes upon drowning insects.
Because the claw of the mandible distils a deleterious liquid, analogous in its nature to that which exudes from the mouth of the scolopendra, and the tail or sting of the scorpion.
The bite of the tarentula spider, was said to produce symptoms equally severe with those of the most malignant fever, and of such a nature, as to be cured only by means of music. Some authors have even given a list of the most restorative tunes.
Because, with their mandibles, resembling a pair of pincers, they compress the small animal on which they prey, and so force the alimentary juices to pass by degrees into the oesophagus. The body of their prey having undergone this operation, is then thrown aside.
A species in the West Indies kills humming-birds, and sucks their eggs. It is the size of a small child's fist; the soles of the feet glitter with gold, etc.
Some species of spider can re-produce lost or mutilated parts, like the crab and lobster. This fact was first observed in this country by Sir Joseph Banks, which gave rise to Dr. Wolcot's well-known satire.
Because they may ascend and descend, cross from tree to tree, across streams, etc.; but whether this is accomplished by projectile force, by the electricity of the atmosphere, or by the mechanical action of the external currents of air, is still a subject of dispute. Messrs. Rennie, and Blackwall, maintain the necessity of a current of air as a moving force; Mr. Murray, Mr. Bowman, and others, maintain a contrary opinion; and Mr. Viray thinks it more probable, that spiders actually fly, by vibrating their feet through the air; he does not assert that they have wings.
Because they catch their prey by the gummed threads of the web, which lose their viscid properties by the action of the air.*
* Leuwenhoeck states, that the threads of the minutest spiders, some of which are not equal in bulk to a grain of sand, are so fine, that four millions of them would not exceed the thickness of a human hair. Each of the four spinners from which the web is spun, is pierced by about 1,000 holes, consequently, every compound or ordinary thread is composed of 40,000 still finer. Thus, a spider's thread, of the thickness of a human hair, may, in some instances, be composed of not fewer than 16,000 millions.
Because they benefit the horses: the more spiders'-webs, the fewer flies.