Fig. 3. Stretching the viscid spiral.
A little attention to the centre of the wheel, and the snare is complete. Some species of Epeira entirely remove the centre, leaving a circular empty space, while others fill it with an irregular network of threads.
How does the garden spider avoid getting caught in its own web? We have shown that there are many lines which are not viscid, and no doubt these are utilised as far as possible, but it can hardly happen that the spider never touches adhesive portions of the web with legs or body.
Possibly some explanation is furnished by an ingenious experiment which Fabre performed. He found that a glass rod, lightly smeared with oil, did not adhere to the viscid spiral; neither did a leg freshly taken from a garden-spider unless allowed to remain in contact for a considerable time. When, however, this leg had been washed with bisulphide of carbon, which dissolves any kind of oily substance, it adhered at once. It would seem likely, therefore, that the legs and body of the spider itself are protected by some oily exudation from any danger of adherence to its own lines.
[CHAPTER IV]
MENTAL POWERS OF SPIDERS
Before leaving the garden-spider let us undertake some little investigation of its mental powers—if it possesses any. The commonest mistake with regard to all animals is to interpret their actions from the human standpoint, and to credit them with emotions and with deliberate forethought of which there is in reality no proof whatever. The power to spin such a complicated snare as we have just described predisposes us to attribute a high order of intelligence to a creature capable of such an achievement, and when it “shams death” on being disturbed we immediately pronounce it “cunning.” The wildest conclusions are sometimes arrived at. One author, for instance, states that he has seen an Attid spider “instructing its young ones how to hunt” and adds that “whenever an old one missed its leap, it would run from the place and hide itself in some crevice as if ashamed of its mismanagement.” Such inferences, of course, were entirely unwarranted from the facts observed. Now the fact that a newly-hatched garden-spider can make a complete snare without ever having seen the operation performed immediately relegates that action to the realm of instinct,—not less wonderful than intelligence perhaps, but certainly quite distinct from it. With the much discussed origin of instinct we are not here concerned, but a pure instinct differs from intelligence in this: that it is due to inherited nervous mechanism and results in actions the object of which may be quite unknown to the actors. There is no conscious adaptation of means to an end. When a young spider spins a web there is not only no evidence that it does so with the deliberate purpose of catching flies, but many known facts go to prove that it performs the feat, “because it feels as if it must,” and is quite ignorant of the purpose to be subserved.
It is no doubt quite beyond our power to ascertain accurately the mental condition of a spider, but it is perfectly easy to make a few illuminating experiments on two points which have a very decided bearing on intelligence:—the development of the senses, and the degree of what has been called educability, or the power of learning from experience. To what extent can the spider see, hear, smell, feel, taste? How far is it capable of varying its action as the result of experience? The senses, as far as we know, are the principal—if not the only—avenues by which external impressions can reach the seat of intelligence, and there is no surer indication of the intelligence of an animal than the degree to which it is susceptible of education. Probably most readers know the immortal story of the pike cited by Darwin in the Descent of Man. The pike was in an aquarium, separated by a sheet of glass from a tank in which were numerous small fish. Not till three months had expired did the pike cease to dash itself against the glass partition in its attempts to seize the fish in the neighbouring tank. It then desisted and had evidently learnt something—but what? After three months, the glass partition was removed, but the pike refused to attack those particular fish, though it immediately seized any new specimens introduced to the tank. All that it had apparently learnt was that an attack on a particular fish resulted in a violent blow on the nose. Some degree of intelligence must be conceded to the pike, but it can hardly be considered of a high order.
Now the garden-spider possesses eight eyes, and might be expected to see fairly well, but the experimenter will very soon come to the conclusion that the habitual use it makes of them—at all events in day-light—is very slight. Touch a web with a vibrating tuning-fork and the spider will rush to the spot and investigate the instrument with its fore-legs before distinguishing it from a fly. Remember, however, that this is only true of what are sometimes called sedentary spiders; species which hunt their prey have much better vision. Yet even among sedentary spiders the power of sight is not negligible, for a most trustworthy observer states that he has several times seen Meta segmentata, a very common small Epeirid, drop from its web to secure an insect on the ground beneath, and return with it by way of the drop line, and the same action has been observed in the case of Theridion, which spins an irregular snare.