1928] The Nesting Habits of the Pulp-Making Bee 
101 
some species of Osmia utilize clay, while others resort to vegetable 
matter. On July 20, 1903, I witnessed ** a female Alcidamea 
producta obtaining her leaf material from a wild strawberry *** 
the leaves of this plant are rather hairy on the under side, and 
when thoroughly chewed they form a felt-like, pliable mass.” 
My St. Louis specimens also failed to behave in just the 
same way as Davidson’s in California; this species, unlike other 
twig-dwelling bees heretofore reported, makes plugs and par- 
titions of a tough, tightly compressed, green substance which 
under the microscope proves to be vegetable fibres, i. e., portions 
of leaves chewed to a fibrous pulp and moistened with saliva, 
which makes wonderfully strong plugs. This material is packed 
down in layers to form the plug, so that each mouthful forms a 
distinct stratum (see four layers at (a) in fig. 1). This is tough 
and well-nigh impenetrable when dry; hence the new adults 
emerging from beneath this roof cannot bite through, and have 
adopted an unusual and ingenious method of effecting their escape. 
A general description of the nest, and the details of a few 
typical courses of action will impart a better idea of this bee’s 
ways. These bees nidify in tunnels of elder, sumac or rose stems. 
Whether they excavate their own burrows or utilize some old 
ones left by other twig-dwellers, I cannot say. No evidence has 
been found of previous occupancy of the galleries; in one or two 
cases we noticed that the nest rested on the very bottom of the 
cavity, and in as many others the gallery seemed much longer 
than this bee had any need of, so the meagre evidence is equally 
divided on this point. The silky cocoons are transparent to a 
degree that gives one a fairly good view of the organism within. 
There is much irregularity in the dimensions of the cells 
and the partitions. A typical series of measurements is as fol- 
lows — length of cells in inches: 1, 5/ 16, 5/ 16, l/ 8, 7/8, 3/8; 
thickness of partitions: l/ 8 , l/ 8 , 1/ 16, l/4, l/4, l/ 8 ; air-space 1 
1/ 2 ; outer plug: 5/8. In fig. 1 is shown a nest of this species, 
natural size, in the twig of elder; at “a” one sees the tight plug 
on the top of the nest, already referred to, and 4 cells are to be 
seen below “p”, which are the partitions made of the fibrous 
vegetable material. 
