Fig. 11. Three “keys” of a stridulating organ, after Spencer.
In Staten Island there is a wolf-spider—Lycosa kochi—which is known as the “purring” or “drumming” spider because of a curious habit which the male has, at mating time, of rapidly drumming on the dead leaves in a wood with its palps. It runs hither and thither over the ground as if in search of something, pausing at short intervals to “purr,” and the sound had frequently been heard and correctly attributed to the spider before the way in which it is produced was discovered. In this case it is probable that the production of sound is not the object of the spider at all, for we have no evidence that wolf-spiders hear. On the other hand rapid tapping with the palps is a very characteristic action with male spiders at mating time, and it is easy to believe that contiguous dry leaves would conduct vibrations to a female at some distance away and inform her of the presence of the male. Just so, as we have seen, our English Theraphosid announces his arrival by tapping on the exposed part of the nest of the female.
[CHAPTER XIII]
THE SPINNING APPARATUS, AND THE FEET
Seeing that the possession of spinnerets is a characteristic of all spiders, and that a great deal of the interest attaching to their life-history arises from their spinning operations, any account of the group, however brief, would be incomplete without some attempt to describe these remarkable organs.
Among the spiders to which the attention of the reader has been directed, some have been highly accomplished spinners, constructing complicated snares, retreats and egg-cocoons, while in the case of others the spinning work is very meagre and employed chiefly for the protection of the eggs. As might be expected, the organs attain a very much higher development in some spiders than in others, and the most complex of all are those of the Epeiridae, the constructors of the circular snare.
Now in the first place it is rather striking that the spiders with the most conspicuous spinnerets are by no means the most able spinners. The “bird-eating” spiders are a case in point, for they spin very little, yet two of their spinnerets are much more obvious than anything Epeira has to show, for they protrude behind the body and strike the eye at the first glance. Indeed excessive length has nothing to do with complexity but is found wherever a wide sweep is necessary in laying down the threads—as we saw in the case of Agelena, when constructing its sheet-web.
Roughly speaking, the spinnerets are very mobile finger-like projections, generally situated under the hind end of the abdomen and, bearing more or less numerous tubes from which the silken threads proceed. The usual number of spinnerets is six, but there is a pretty wide range, one group of spiders having only two, while a few possess eight.