1930] 
Nesting habits of Prosopis 
173 
THE NESTING HABITS OF THE TWIG-DWELLING 
BEE, PROSOPIS MODESTUS SAY 1 
By Phil Rau 
Kirkwood, Mo. 
The nests of this little bee were always found, in my 
experience, in the top hollows of sumac twigs. Only 
the upper part of the cavity was used — usually 21/2 or 3 
inches, never more. Traces of mud partitions and various 
other relics in the lower, unused portion made it evident 
that the tunnels had been used before, but whether this 
bee always uses old borrowed burrows or whether she may 
sometimes do her own excavating I cannot say positively. 
The young of this species construct very thin and trans- 
parent, delicate cocoons which entirely cover the body. 
The cocoons are close together and between them are heavy 
dividing walls, but I have not yet been able to tell with 
certainty whether these disc-like walls are actually par- 
titions of waxy substance built by the mother, or whether 
they are only the front wall or head-piece of each cocoon. 
These disc-like walls are semi-transparent in the center, 
and pale yellow, grading to a dark brown color and to 
greater thickness at the edges. The compact little cocoons, 
of brittle material which resembles the central portion of 
the hard disc, are packed in very close together, so close in 
fact that frequently two adhere to each other. 
A good example of most of these characteristics was a 
little nest which was discovered in a twig in a park in 
iRegarding the identity of this species, I quote from a letter from 
Prof. T. D. A. Cockerell. The bee is “Prosopis modestus Say in the 
sense of Metz (1911). Your male seems to agree with P. minyra 
Lovell {modestus var. according to Metz). The female minyra has 
not been distinguished from that of modestus. It will be necessary 
to collect series of your insect to make sure what it should be called, 
but it is modestus in the broad sense.” 
