160 BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. VOL. 3, NO. 4. 
parasite is about half as long, as the young host. When fully de- 
veloped the larva of Alcidamea spins its cocoon, hibernates as a 
"resting larva," pupates in spring, and emerges some time in 
June. The same applies to its parasite Stelis sexmaculata, al- 
though its time of flight begins somewhat later than that of 
Alcidamea. 
The habits of Alcidamea producta and its parasite Stelis 
sexmaculata agree in a general way with those of Osmia leucome- 
laena and its parasite Stelis minuta as described by Verhoeff , but 
in several important points they differ very decidedly. Verhoeff 
informs us that the larva of the parasite at first equals in size the 
host-larva, but that at the time of the attack it has become twice 
as large as the latter. He also states that after a combat has 
taken place between the two the host-larva succumbs to the at- 
tack of the larger, and more powerful parasite, and is eaten up 
by the latter in the course of a day or two. 
The whole information derived from the study of Alcidamea 
producta and Stelis sexmaculata points to the aggressive instincts, 
and the sharp mandibles of the parasitic larva as the factors de- 
termining the fate of the host-larva. The size and strength of 
the parasitic larva have little, if any influence on the outcome. 
From the start the parasite is only one-half as long as the host, 
and at the time of the attack it may be of only one-fourth the 
length of the Alcidamea-larva, and still perform its deadly work 
with perfect success. The host-larva is doomed from the begin- 
ning. The encounter between the two is an extremely one-sided 
affair, and can not be called a combat, since the acts of hostility 
are evident on the side of the parasite only. The latter instinct- 
ively attacks any larva within its reach, and destroys a larva of its 
own kind in the same manner as it does the host-larva. If there 
be two or more parasites within the same cell all but one will 
have to perish. The victor invariably takes up a large portion 
of the liquid contents of the dead larva, but was never seen to 
eat up the latter entirely. Its essential food is the mixed supply 
of honey and pollen stored away bv the host-bee. On this it 
feeds after leaving the egg, and to this it returns soon after the 
death of its victim. 
BEES OF THE GENUS CCELIOXYS TN THE NESTS OF LEAF- 
CUTTER BEES. 
1. Cwelioxys lucrosa Cress*. A parasite of Megachile 
addenda Cress. 
The leaf-cutter bee Megachile addenda selects the de- 
