"The tunnels are sometimes taken possession of by other bees and wasps. I think when this is the case, the Xylocopa prefers making a new cell, to cleaning out the dirt and rubbish of the other species. I frequently find these bees remaining for a long time on the wing close to the opening, and bobbing their heads against the side, as if fanning air into the opening. I have seen them thus employed for twenty minutes. Whether one bee or more makes the tunnel, that is, whether they take turns in boring, I cannot at present say. In opening the cells (Fig. 21), more than one are generally found, even at this season. About two weeks ago; I found as many as seven, I think, in one."[3]
22. Nest of
Ceratina.
The hole is divided by partitions into cells about seven-tenths of an inch long. These partitions are constructed of the coarse dust or chippings made by the bee in eating out her cells, for our active little carpenter is provided with strong cutting jaws, moved by powerful muscles, and on her legs are stiff brushes of hair for cleaning out the tunnel as she descends into the heart of the solid wood. She must throw out the chips she bites off with her powerful mandibles from the sides of the burrow, by means of her hind legs, passing the load of chips backwards out of the cell with her fore limbs, which she uses as hands.
The partitions are built most elaborately of a single flattened band of chips, which is rolled up into a coil four layers deep. One side, forming the bottom of the cell, is concave, being beaten down and smoothed off by the bee. The other side of the partition, forming the top of the cell, is flat and rough.
At the time of opening the burrow, July 8th, the cells contained nearly full-grown larvæ, with some half developed. They were feeding on the masses of pollen, which were as large as a thick kidney bean, and occupied nearly half the cell. The larvæ (Fig. 21) resemble those of the Humble bee, but are slenderer, tapering more rapidly towards each end of the body.
The habits and structure of the little green Ceratina ally it closely with Xylocopa. This pretty bee, named Ceratina dupla by Mr. Say, tunnels out the stems of the elder or blackberry, syringa, or any pithy shrub, excavating them often to a depth of six or seven inches. She makes the walls just wide enough to admit her body, and of a depth capable of holding three or four, often five or six cells (Fig. 22). The finely built cells, with their delicate silken walls, are cylindrical and nearly square at each end, though the free end of the last cell is rounded off. They are four and a half tenths of an inch long, and a little over one-third as broad. The bee places them at nearly equal distances apart, the slight interval between them being filled in with dirt.
23. Larva of Ceratina.
Dr. T. W. Harris states that May 15, 1832, one female laid its eggs in the hollow of an aster stalk. Three perfect insects were disclosed from it July 28th. The observations of Mr. Angus, who saw some bees making their cells May 18th, also confirm this account. The history of our little upholsterer is thus cleared up. Late in the spring she builds her cells, fills them with pollen, and lays one or more eggs upon each mass. Thus in about two months the insect completes its transformations; within this period passing through the egg, the larva and chrysalid states, and then, as a bee, living a few days more, if a male; or if a female, living through the winter. Her life thus spans one year.