r original position whilst
excavating; and thirdly, her constantly going over work which had
apparently been completed.... The lid is excavated and rendered concave
on its outer or upper surface, and is convex and rough on its inner
surface; and, in fact, is a simple repetition of the first-formed
portion of the cell, a part of a hollow sphere."

The largest species of Osmia known to us is a very dark-blue species (O.
lignivora). We are indebted to a lady for specimens of the bees with
their cells, which had been excavated in the interior of a maple tree
several inches from the bark. The bee had industriously tunnelled out
this elaborate burrow (Fig. 26), and, in this respect, resembled the
habits of the Carpenter bee more closely than any other species of its
genus.

The tunnel was over three inches long, and about three-tenths of an inch
wide. It contracted a little in width between the cell, showing that the
bee worked intelligently, and wasted no more of her energies than was
absolutely necessary. The burrow contained five cells, each half an inch
long, being rather short and broad, with the hinder end rounded, while
the opposite end, next to the one adjoining, is cut off squarely. The
cell is somewhat jug-shaped, owing to a slight constriction just behind
the mouth. The material of which the cell is composed is stout, silken,
parchment-like, and very smooth within. The interstices between the
cells are filled in with rather coarse chippings made by the bee.

The bee cut its way out of the cells in March, and lived for a month
afterwards on a diet of honey and water. It eagerly lapped up the drops
of water supplied by its keeper, to whom it soon grew accustomed, and
seemed to recognize.

Our smallest and most abundant species is the little green Osmia
simillima. It builds its little oval, somewhat urn-shaped cells against
the roof of the large deserted galls of the oak-gall fly (Diplolepis
confluentus), placing them, in this instance eleven in number, in two
irregular rows, from which the mature bees issue through a hole in the
gall (Fig. 27, with two separate cells). The earthen cells, containing
the tough dense cocoons, were arranged irregularly so as to fit the
concave vault of the larger gall, which was about two inches in
diameter. On emerging from the cell the Osmia cuts out with its powerful
jaws an ovate lid, nearly as large as one side of the cell.

[Illustration: 27. Nest of Osmia in a gall.]

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