In the spinning-mills of the carnivorous Wasps, two methods of manufacture are employed to give the silken fabric greater toughness. On the one hand, the fabric is encrusted with numerous grains of sand, which produces an almost mineral shell wherein the silk has no other function than to serve as a cement for the stony materials. That is how the Bembeces, the Stizi, the Tachytes and the Palari work. On the other hand, the larva elaborates in its [[103]]stomach, in its chylific ventricle, a liquid varnish which it disgorges into the meshes of a rudimentary tissue of silk. Directly it trickles into the web, the varnish hardens and becomes a lacquer of exquisite daintiness. The larva next ejects at the base of the cocoon, in the form of a hard stercoral plug, the residue of the chemical process accomplished in its stomach for the elaboration of the varnish. This method is that of the Spheges, the Ammophilæ and the Scoliæ, who varnish the inner wrapper of their multiple cocoons; and of the Crabro-wasps, the Cerceres and the Philanthi,[13] whose delicate cocoon consists of only a single thickness.
The Pelopæus adopts this last procedure. When finished, her work is an amber-yellow fabric suggesting the outer skin of an onion in fineness, colour, transparency and the rustling sound which it emits when fingered. Relatively long in comparison with its width, as is demanded by the capacity [[104]]of the cell and the slender form of the future insect, the cocoon is rounded at the top and suddenly truncated at the base, which is rendered hard and opaque by the stercoral plug, the by-product of the lacquer-factory.
The hatching-period varies, of course, according to the temperature and also according to certain conditions which I am not yet in a position to specify. One cocoon, woven in July, gives birth to the perfect insect in the course of August, two or three weeks after the larva’s period of activity; another, dating from August, opens a month later, in September; a third, no matter what its date of origin during the summer quarter, goes through the winter and does not burst until the end of June. By combining the birth-certificates recorded, I seem to distinguish three generations in the year, generations which are often but not invariably realized. The first appears at the end of June: this is the one whose cocoons have gone through the winter; the second is seen in August and the third in September. So long as the very hot weather lasts, evolution is rapid: three or four weeks suffice to complete the Pelopæus’ cycle. When September arrives, the fall in [[105]]temperature puts an end to these precocious broods; and the last larvæ have to wait for the return of the hot weather before they can undergo their transformation. [[106]]
[1] For the various species of Burrowing Bees known as the Anthophoræ, cf. Bramble-bee and others: chap. vii. et passim.—Translator’s Note. [↑]
[2] For the Cicada, or Cigale, cf. The Life of the Grasshopper, by J. Henri Fabre, translated by Alexander Teixeira de Mattos: chaps. i. to v.—Translator’s Note. [↑]
[3] The Pompilus, or Ringed Calicurgus, is a Hunting Wasp, feeding her young on Spiders. Cf. The Life and Love of the Insect: chap. xii.—Translator’s Note. [↑]
[4] For the Epeiræ, or Garden Spiders, cf. The Life of the Spider: chaps. ix. to xiv.—Translator’s Note. [↑]
[5] One of the Tube-weaving Spiders.—Translator’s Note. [↑]
[6] For Theridion lugubre and the Narbonne Lycosa, or Black-bellied Tarantula, cf. The Life of the Spider: chap. i.—Translator’s Note. [↑]