Insect Architecture

by James Rennie

This species is notable for the many parasites who infect the habitation and destroy the inmates. Perhaps the very worst and most destructive of these parasites is the common earwig, which wreaks wholesale desolation in the nest. It creeps into the burrow, and if it finds a store of pollen laid up for the young, it will eat the pollen. But if the young grub be hatched it will eat the grub. If the inmate be in the pupal state, or even if it be ready to emerge in its perfect condition, the earwig will eat it.

There are two bees which are parasitic upon this unfortunate insect, both belonging the genus Melecta.

But the most destructive of these parasites appears to be an insect which belongs to the great family of Chalcididæ. These insects are of the hymenopterous order, are of very minute dimensions, and of the most brilliant colours. Indeed, if they were an inch or two in length, instead of the eighth or twelfth of an inch, they would not suffer in comparison with the most gorgeous inhabitants of tropical countries.

Their forms are most eccentric, some species having the abdomen small and round and set on a long footstalk, while others have that portion of the body placed so closely against the thorax, that the short footstalk is scarcely visible. Others have certain joints of the legs so large that a single joint equals the entire abdomen. Some have the ovipositor projecting boldly from the body, while others have it tucked up underneath, and others again have it quite short. But there is one point which distinguishes them all, namely, the almost veinless character of the wings.

Some of the Chalcididæ are parasitic upon insects in their earliest stages, actually depositing their eggs in those of moths and butterflies. Others are entirely parasitic upon parasites, laying their eggs in the aphidii, which are parasites of the aphis. Some of them haunt the galls, and contrive to make their young parasitic upon the immature cynipidæ which lie within the gall. The common small tortoise-shell butterfly is terribly infested with these little creatures, and we have bred hundreds of the gem-like Chalcididæ from the larvæ and pupæ of that butterfly.

One of the Chalcididæ, belonging to the genus Melittobia, is a parasite upon the Anthophora; and the curious part of the proceeding is, that it finds there another parasite, which becomes developed in the home of the bee: the Melittobia feeds indiscriminately upon the bee and parasite.

Although the Melittobia does not make such wholesale destruction as is wrought by the earwig when it gets into a nest, it does more damage to the bee, on account of its great numbers. Some three or four females will lay a great quantity of eggs within a nest, and from those eggs a hundred of the young will be developed. When the larvæ are fully grown, they quit their hold of their prey, and fall to the bottom of the cell, where they lie until they have assumed the perfect form. They then burst forth, together with those of the bee that may have escaped their attacks.]

An interesting account is given by Réaumur of another mason-bee (Megachile muraria), not a native of Britain, selecting earthy sand, grain by grain; her glueing a mass of these together with saliva, and building with them her cells from the foundation. But the cells of the Greenwich Park nest were apparently composed of the mortar of the brick wall; though the external covering seems to have been constructed as Réaumur describes his nest, with the occasional addition of small stones.

About the middle of May, 1829, we discovered the mine from which all the various species of mason-bees in the vicinity seemed to derive materials for their nests. (J. R.) It was a bank of brown clay, facing the east, and close by the margin of the river Ravensbourn, at Lee, in Kent. The frequent resort of the bees to this spot attracted the attention of some workmen, who, deceived by their resemblance to wasps, pointed it out as a wasps’ nest; though they were not a little surprised to see so numerous a colony at this early season. As the bees had dug a hole in the bank, where they were incessantly entering and reappearing, we were of opinion that they were a peculiar sort of the social earth-bees (Bombi). On approaching the spot, however, we remarked that the bees were not alarmed, and manifested none of the irritation usual in such cases, the consequence of jealous affection for their young. This led us to observe their operations more minutely; and we soon discovered that on issuing from the hole each bee carried out in its mandibles a piece of clay. Still supposing that they were social earth-bees, we concluded that they were busy excavating a hollow for their nest, and carrying off the refuse to prevent discovery. The mouth of the hole was overhung, and partly concealed, by a large pebble. This we removed, and widened the entrance of the hole, intending to dig down and ascertain the state of the operations; but we soon found that it was of small depth. The bees, being scared away, began scooping out clay from another hole about a yard distant from the first. Upon our withdrawing a few feet from the first hole, they returned thither in preference, and continued assiduously digging and removing the clay. It became obvious, therefore, from their thus changing place, that they were not constructing a nest, but merely quarrying for clay as a building material. By catching one of the bees (Osmia bicornis) when it was loaded with its burden, we ascertained that the clay was not only carefully kneaded, but was also more moist than the mass from which it had been taken. The bee, therefore, in preparing the pellet, which was nearly as large as a garden-pea, had moistened it with its saliva, or some similar fluid, to render it, we may suppose, more tenacious, and better fitted for building. The reason of their digging a hole, instead of taking clay indiscriminately from the bank, appeared to be for the purpose of economizing their saliva, as the weather was dry, and the clay at the surface was parched and hard. It must have been this circumstance which induced them to prefer digging a hole, as it were, in concert, though each of them had to build a separate nest.