The bits of gravel in the lid are angular and chalky in the Marseilles nest; they are round and flinty in most of the Serignan nests. In making her mosaic, the worker pays no heed to the form or colour of its component parts; she collects indiscriminately anything that is hard enough and not too large. Sometimes she lights upon treasures that give her work a more original character. The Marseilles nest shows me, neatly encrusted amid the bits of gravel, a tiny whole landshell, Pupa cineres. A nest in my own neighbourhood provides me with a pretty Snail-shell, Helix striata, forming a rose-pattern in the middle of the mosaic. These little artistic details remind me of a certain nest of Eumenes Amadei (A Mason-wasp, forming the subject of an essay which has not yet been published in English.--Translator's Note.) which abounds in small shells. Ornamental shell-work appears to number its lovers among the insects.
After the lid of resin and gravel, an entire whorl of the spiral is occupied by a barricade of incongruous remnants, similar to that which, in the reeds, protects the row of cocoons of the Manicate Cotton-bee. It is curious to see exactly the same defensive methods employed by two builders of such different talents, one of whom handles flock, the other gum. The nest from Marseilles has for its barricade bits of chalky gravel, particles of earth, fragments of sticks, a few scraps of moss and especially juniper-catkins and needles. The Serignan nests, installed in Helix aspersa, have almost the same protective materials. I see bits of gravel, the size of a lentil, and the catkins and needles of the brown-berried juniper predominating. Next come the dry excretions of the Snail and a few rare little land-shells. A similar jumble of more or less everything found near the nest forms, as we know, the barricade of the Manicate Cotton-bee, who is also an adept at using the Snail's stercoral droppings after these have been dried in the sun. Let us observe finally that these dissimilar materials are heaped together without any cementing, just as the insect has picked them up. Resin plays no part in the mass; and we have only to pierce the lid and turn the shell upside down for the barricade to come dribbling to the ground.
To glue the whole thing together does not enter into the Resin-bee's scheme. Perhaps such an expenditure of gum is beyond her means;perhaps the barricade, if hardened into a solid block, would afterwards form an invincible obstacle to the escape of the youngsters; perhaps again the mass of gravel is an accessory rampart, run up roughly as a work of secondary importance.
Amid these doubtful matters, I see at least that the insect does not look upon its barricade as indispensable. It employs it regularly in the large shells, whose last whorl, too spacious to be used, forms an unoccupied vestibule; it neglects it in the moderate shells, such as Helix nemoralis, in which the resin lid is level with the orifice. My excavations in the stone-heaps supply me with an almost equal number of nests with and without defensive embankments. Among the Cotton-bees, the Manicate Anthidium is not faithful either to her fort of little sticks and stones; I know some of her nests in which cotton serves every purpose. With both of them, the gravel rampart seems useful only in certain circumstances, which I am unable to specify.
On the other side of the outworks of the fortification, the lid and barricade, are the cells set more or less far down in the spiral, according to the diameter of the shell. They are bounded back and front by partitions of pure resin, without any encrustations of mineral particles. Their number is exceedingly restricted and is usually limited to two. The front room, which is larger because the width of the passage goes on increasing, is the abode of a male, superior in size to the other sex; the less spacious back room contains a female. I have already drawn attention in an earlier chapter to the wonderful problem submitted for our consideration by this breaking up of the laying into couples and this alternation of the males and females. Without calling for other work than the transverse partitions, the broadening stairway of the Snail-shell thus furnishes both sexes with house-room suited to their size.
The second Resin-bee that inhabits shells, Anthidium bellicosum, hatches in July and works during the fierce heat of August. Her architecture differs in no wise from that of her kinswoman of the springtime, so much so that, when we find a tenanted Snail-shell in a hole in the wall or under the stones, it is impossible to decide to which of the two species the nest belongs. The only way to obtain exact information is to break the shell and split the cocoons in February, at which time the nests of the summer Resin-bee are occupied by larvae and those of the spring Resin-bee by the perfect insect. If we shrink from this brutal method, we are still in doubt until the cocoons open, so great is the resemblance between the two pieces of work.
In both cases, we find the same lodging, Snail-shells of every size and every kind, just as they happen to come; the same resin lid, the inside gritty with tiny bits of stone, the outside almost smooth and sometimes ornamented with little shells; the same barricade--not always present--of various kinds of rubbish; the same division into two rooms of unequal size occupied by the two sexes. Everything is identical, down to the purveyor of the gum, the brown-berried juniper. To say more about the nest of the summer Resin-bee would be to repeat oneself.
