All the remarkable and apparently intelligent actions of these creatures seem to be done in obedience to a blind instinct, which is obeyed even when there is no longer any object to be served. We have seen how the Trap-door spiders decorate the lids of their nests with moss even when the surrounding ground is bare, and Agelena labyrinthica has been observed to go through the whole lengthy and laborious operation of constructing its egg-cocoon though all its eggs were removed immediately on being laid.[[302]]
Mating Habits.—The sex of a mature spider can readily be recognised by the palpus which, as we have seen, is furnished in the male with a “palpal organ.” After the last moult but one the palp appears tumid, but it is only at the last moult that the organ is fully formed, and that the genital orifice is visible under the anterior part of the abdomen.
No alteration takes place in the female palp at maturity, but it is only after the last moult that the “epigyne” is distinguishable.
Fig. [198].—Argiope aurelia, ♂ and ♀, natural size.
That the palpal organs are used in the fertilisation of the female has long been established. How they came to contain the sperm matured in the abdomen was a problem which has only been solved comparatively recently. No direct connection could be found by way of the palpus with the abdominal organs, which, indeed, were seen to have an orifice between the lung-sacs. It is now known that some spiders at all events spin a slight web upon which they deposit a drop of spermatic fluid, which they afterwards absorb into their palpal organs for transference to the female. Secondary sexual differences are often very marked, the male being almost invariably the smaller in body, though its legs are frequently longer and more powerful than those of the female.
Among some of the sedentary spiders the disparity in size is excessive. The most striking examples are furnished by the Epeirid genera Argiope and Nephila, the male in some instances not attaining more than the thousandth part of the mass of the female. The coloration of the sexes is frequently quite dissimilar, the male being usually the darker, though in the Attidae he is in many cases the more strikingly ornamented.
In the minute Theridiid spiders of the group Erigoninae (see p. 404), the male cephalothorax often presents remarkable and characteristic excrescences not observable in the female. Some curious examples of this phenomenon may be seen in Fig. [209].
To the ordinary observer male spiders will appear to be comparatively rare, and to be greatly outnumbered by the females. This is probably to some degree true, but the unsettled habits of the males and the shorter duration of their life are calculated to give an exaggerated impression of their rarity. They only appear in considerable numbers at the mating season, shortly after which the males, in the case of many species, may be sought for in vain, as, after performing their functions, they quickly die. The snares they spin are often rudimentary, their capabilities in this direction appearing to deteriorate after the adult form is attained. Young spiders of indistinguishable sex make perfect snares on a small scale, while such as eventually develop male organs will often thereafter be content with a few straggling lines made with very slight regard to symmetry. They become nomadic in their habits, wandering off in search of the females, and pitching a hasty tent by the way.
The relations between the sexes in the Spider tribe present points of extreme interest, but in this connexion the various groups must be separately treated on account of their very different habits of life.