Whether or not this second explanation is the true one, we have not the means of ascertaining; but we are almost certain the first is incorrect, as it is contrary to the regular procedure of insects to begin with the interior part of any structure, and work outwards. We should imagine, then, that the down is first spread out into the form required, and afterwards plastered on the inside to keep it in form, when probably the grub spins the vermicular cells previous to its metamorphosis.
It might prove interesting to investigate this more minutely; and as the bee is by no means scarce in the neighbourhood of London, it might not be difficult for a careful observer to witness all the details of this singular architecture. Yet we have repeatedly endeavoured, but without success, to watch the bees, when loaded with down, to their nests. The bee may be readily known from its congeners, by its being about the size of the hive-bee, but more broad and flattened, blackish-brown above, with a row of six yellow or white spots along each side of the rings, very like the rose-leaf cutter, and having the belly covered with yellowish-brown hair, and the legs fringed with long hairs of a rather lighter colour.
* * * * *
[This bee does not bore a tunnel for herself, but occupies that of some other insect. The nests of this insect are generally to be obtained from old willows, because these trees are so largely bored by the goat-moth caterpillar, and afford ample space for the larva. The woolly substance obtained from the plant is pressed against the sides of the burrow, so as to form a lining. She then makes a series of cells of a similar material, and the young larva, when it is about to change into the pupa state, envelops itself in a silken covering of a brown colour.
It is a curious fact, that the male of this insect is considerably larger than the female, thus reversing the usual order of things among insects. Only one species of this bee is known in England.]
A common bee belonging to the family of upholsterers is called the rose-leaf cutter (Megachile centuncularis, Latr.). The singularly ingenious habits of this bee have long attracted the attention of naturalists; but the most interesting description is given by Réaumur. So extraordinary does the construction of their nests appear, that a French gardener having dug up some, and believing them to be the work of a magician, who had placed them in his garden with evil intent, sent them to Paris to his master, for advice as to what should be done by way of exorcism. On applying to the Abbé Nollet, the owner of the garden was soon persuaded that the nests in question were the work of insects; and M. Réaumur, to whom they were subsequently sent, found them to be the nests of one of the upholsterer-bees, and probably of the rose-leaf cutter, though the nests in question were made of the leaves of the mountain ash (Pyrus aucuparia).
The rose-leaf cutter makes a cylindrical hole in a beaten pathway, for the sake of more consolidated earth (or in the cavities of walls or decayed wood), from six to ten inches deep, and does not throw the earth dug out from it into a heap, like the Andrenæ.[S] In this she constructs several cells about an inch in length, shaped like a thimble, and made of cuttings of leaves (not petals), neatly folded together, the bottom of one thimble-shaped cell being inserted into the mouth of the one below it, and so on in succession.
Rose-leaf cutter Bees, and Nest lined with rose-leaves.
It is interesting to observe the manner in which this bee procures the materials for forming the tapestry of her cells. The leaf of the rose-tree seems to be that which she prefers, though she sometimes takes other sorts of leaves, particularly those with serrated margins, such as the birch, the perennial mercury (Mercurialis perennis), mountain-ash, &c. She places herself upon the outer edge of the leaf which she has selected, so that its margin may pass between her legs. Turning her head towards the point, she commences near the footstalk, and with her mandibles cuts out a circular piece with as much expedition as we could do with a pair of scissors, and with more accuracy and neatness than could easily be done by us. As she proceeds, she keeps the cut portion between her legs, so as not to impede her progress; and using her body for a trammel, as a carpenter would say, she cuts in a regular curved line. As she supports herself during the operation upon the portion of the leaf which she is detaching, it must be obvious, when it is nearly cut off, that the weight of her body might tear it away, so as to injure the accuracy of its curvilineal shape. To prevent any accident of this kind, as soon as she suspects that her weight might tear it, she poises herself on her wings, till she has completed the incision. It has been said, by naturalists, that this manœuvre of poising herself on the wing, is to prevent her falling to the ground, when the piece gives way; but as no winged insect requires to take any such precaution, our explanation is probably the true one.