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The straw-coloured thread, drawn from the silk-glands by a backward jerk of the head, is first fixed to the white network of the caterpillar and then produces adjacent warp-beams, so that, by mutual entanglements, the individual works are welded together and form an agglomeration in which each of the grubs has its own cabin.
If my surmise is well-founded, there is reason to believe that, with a view to speedily filling the silk-glands to which they look to supply them with ropes, other caterpillars beginning their existence on smooth and steeply-slanting leaves also take as their first mouthful the membranous sack which is all that remains of the egg.
To protect himself against the severity of the winter which he has to face when working, the Pine Caterpillar weaves himself a shelter in which he spends his bad hours, his days of enforced idleness. Alone, with none but the meagre resources of his silk-glands, he would find difficulty in protecting himself on the top of a branch buffeted by the winds.
The inner envelope is firm, elastic, rigid and, to a certain point, brittle. I do not hesitate to look upon it as consisting of a silken tissue which the larva, towards the end of its task, has steeped thoroughly in a sort of varnish prepared not by the silk-glands but by the stomach. The cocoons of the Sphex have already shown us a similar varnish.
The walls never seem thick enough; the Spider is always working at them. To satisfy this lavish expenditure, she must incessantly, by means of feeding, fill her silk-glands as and when she empties them by spinning. Food is the means whereby she keeps the inexhaustible factory going.
Concerning the modifications of structure and the instincts necessary to produce the web of the spider, Fairhurst quotes the following from Orton's "Zoology." The office of the spinnerets is to reel out the silk from the silk-glands, the tip being perforated by a myriad of little tubes through which the silk escapes in excessively fine threads.
Then, until the quarry is thoroughly subdued, the spray of bandages goes on continuously, even to the point of drying up the silk-glands. A capture of this kind is ruinous. It is true that, except when I interfered, I have never seen the Spider tackle that formidable provender. Be it feeble or strong, the game is now neatly trussed, by one of the two methods. The next move never varies.
The silk-glands may be exhausted after the laying of the great spiral; and to repeat the same expenditure immediately is out of the question. I want a case wherein there could be no appeal to any such exhaustion. I obtain it, thanks to my assiduity. While I am watching the rolling of the spiral, a head of game rushes fun tilt into the unfinished snare.
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