A little later in the summer the appearance of a troop of wolf-spiders has undergone a marked change; almost every individual will be found burdened with a circular bag of eggs attached firmly to its spinnerets, and carried about with it in all its wanderings.
Fig. 7. Wolf-spiders; A, with egg-cocoons; B, with young on its back.
The “cocoon” is worth examination. It is a rather flattened sphere, with an equatorial line round it, giving the effect of two halves—an upper and a lower. The operation of making it has very seldom been observed, because it takes place in a closed retreat constructed for the purpose. McCook was fortunate enough to see something of it in the case of a captive Lycosa which he kept in a glass jar partly filled with soil. Luckily the spider dug its tunnel for cocooning purposes up against the side of the jar, so that its interior was visible. It was about an inch deep and fairly wide, and its aperture was closed with silk.
Against the perpendicular wall of soil a circular silken cushion about three quarters of an inch in diameter was spun, and the eggs deposited in the centre. The edges of the cushion were then gathered up and pulled over the eggs, and the bag thus formed was finished off with an external layer of spinning work on the two halves of the sphere, the seam or “equator” being left thin for the exit of the young spiders. The Lycosa then attached the cocoon to its spinnerets and proceeded to bite away the silken sheet which sealed the burrow. The whole operation lasted about four and a half hours.
Thenceforward, till the young are hatched, the wolf-spider never quits her egg-bag, which she carries about on all her expeditions attached by threads to the spinnerets. Garden-spiders die soon after laying their eggs and never see their progeny, but here we have a case of maternal solicitude persisting for many days, and the Peckhams seized upon it as a good subject for investigating the subject of the memory of spiders. If the cocoon were removed from the spinnerets, after how long an interval would it be recognised by the mother?
A Pirata was selected for experiment. It offered great resistance to the removal of the cocoon, seizing it with its jaws and trying to escape with it. When it had been taken away the mother displayed great uneasiness, searching for it in all directions. It was returned to her after an hour and a half, when she received it eagerly and immediately attached it in the usual position.
From three others of the same species the cocoons were removed and restored after thirteen, fourteen and a half, and sixteen hours respectively. All remembered them and took them back immediately. But twenty-four hours seemed to be the extreme limit of their memory; after that interval two of the mothers refused to have anything to do with their cocoons, while the third only resumed hers, slowly and without any enthusiasm, after it had been placed before her seven times in succession. Some other species seemed to possess a rather longer memory, but the experimenters found no Lycosid constant in her affection for so long a period as forty-eight hours.