The jumping spiders furnish a much stronger case for those who believe that ornamentation plays an important part in sexual selection than do either birds or butterflies. With regard to the birds it has been objected, first, that there is little evidence that the females pay much attention to the antics of the males, and secondly, that practically all the male birds pair, whatever their claims to pre-eminent beauty. Now in the case of the jumping spiders the females follow the performances of the males with the utmost attention, and seeing that the males are present in large numbers when the females begin to appear, the latter are certainly in the position to reject such mates as do not please them.
The mere relation of the results of this most interesting investigation conveys no hint of the unwearied patience and close observation necessary to those who would surprise the secrets of nature. One is apt to infer that it is only needful to place some spiders in a box, establish oneself in an arm chair, and ring on the performance, so to speak. The Peckhams modestly remark: “The courtship of spiders is a very tedious affair. We shall condense our descriptions as much as possible, but it must be noted that we often worked four or five hours a day for a week in getting a fair idea of the habits of a single species.”
[CHAPTER XI]
THERAPHOSID SPIDERS
It is quite impossible in a work like the present to deal with the classification of spiders. About forty families have been established, some of them of vast extent, the Attidae, for example, including some four thousand species. The great French arachnologist, M. E. Simon, has occupied 2,000 quarto pages in defining the families, sub-families and genera, without concerning himself with the species at all! It is, however, desirable, that the attention of the reader should be called to the primary division of the group, according to which all spiders are either Araneae verae (true spiders) or Araneae theraphosae (theraphosid spiders.)
Now these two kinds of spider may readily be distinguished by a single easily observable characteristic, the nature of the mandibles or chelicerae; but it is necessary to describe the spider’s mandibles before the difference can be appreciated.
Their nature is perhaps best explained by saying that each mandible is not unlike a penknife with a single small blade, rather more than half open when in use, closed when at rest. The handle of the penknife is certainly in most cases very short and thick, and the blade not really a blade at all, for it has no cutting edge, but is a “fang” or piercing instrument generally somewhat curved, and with a sharp point. The “blade” is, moreover, perforated by a tube which comes from the poison-gland, situated in the thickened “handle,” or in the spider’s head, so that poison can be forced into the wound which it inflicts.
Now take two penknives with the blades half open and hold them so that they hang with the hinge downward and with the blades directed towards each other; it is clear that the blades may be made to pierce an object situated between them by moving the handles laterally, the object being attacked simultaneously on either side. This is the arrangement in the true spiders, whose jaws move sideways, though they do not always hang perpendicularly, but are more often somewhat slanted forwards.
To represent the jaws of a theraphosid spider the penknives must be arranged differently. Place the handles horizontally and parallel to each other, with the blades directed downwards and also parallel. They will now work not sideways, but up and down, and both fangs will pierce the victim from above. In a word, the true spiders have jaws which can be separated or brought together, and which tend to meet in the object into which they are plunged, while the jaws of theraphosid spiders work in parallel vertical planes, and strike downwards.