.
Fig. 54.—Jumping Spider. (Line shows natural size.)
Fig. 55.—Falces of Male Jumping Spider.
It requires some little practice to detect the eyes of spiders and to remember their position in the different genera, but by examining every spider met with, and consulting some handbook to the group, one will soon be able to determine the commoner British species.
With a couple of needles we may remove the falces (Fig. 55) for examination; and there is no difficulty in mounting them, as shown in the cut, on a piece of card, so that they may be compared with the same weapons in other species. For example, the falces of the Garden Spider differ from those of the Jumping Spider in that they are short and stout, and the teeth on the basal joint are more in number.
The following account of the habit of this spider in capturing prey is from Kirby and Spence’s Introduction to Entomology (ed. 1870, p. 453):—‘When these insects spy a small gnat or fly upon a wall, they creep very gently towards it with short steps, till they come within a convenient distance, when they spring upon it suddenly like a tiger. Bartram observed one of these spiders that jumped two feet upon a humble-bee. The most amusing account, however, of the motions of these animals is given by the celebrated Evelyn in his Travels. When at Rome, he often observed a spider of this kind hunting the flies which alighted upon a rail on which was its station. It kept crawling under the rail till it arrived at the part opposite to the fly, when stealing up it would attempt to leap upon it. If it discovered that it was not perfectly opposite, it would immediately slide down again unobserved, and at the next attempt would come directly upon the fly’s back. Did the fly happen not to be within a leap, it would move towards it so softly, that its motion seemed not more perceptible than that of the shadow of the gnomon of a dial. If the intended prey moved, the spider would keep pace with it as exactly as if they were actuated by one spirit, moving backwards, forwards, or on each side without turning. When the fly took wing, and pitched itself behind the huntress, she turned round with the swiftness of thought, and always kept her head towards it, though to all appearance as immovable as one of the nails driven into the wood on which was her station: till at last, being arrived within due distance, swift as lightning she made the fatal leap and secured her prey.’
This spider employs a clever precaution against falling, when about to spring upon its prey. It applies the end of the abdomen to the surface on which it stands, and opening its spinnerets, makes an ‘anchorage’ (Fig. 56). Then, by the act of springing, it draws from the spinnerets a line attached to the spot from which it started. This line is strong enough to support the spider in case it misses its prey.