NOVEMBER, 1905. SOME OBSERVATIONS ON PARASITIC BEES. 
157 
bread and growing in length reached the second and killed it. 
Four days later this same parasite killed the uppermost one and 
fed' on its contents. Two days after this (July 21), the surviving 
parasite killed the host-larva. Both were about equal in size. 
From the study of these 2 infested cells, as also of the remain- 
ing material at my disposal, we are presented with several note- 
worthy facts concerning the instincts of this particular parasitic 
larva. The most conspicuous feature is the pronounced aggres- 
sive tendency of the larva of Stelis sexmaculata as compared with 
the rather tolerant demeanor of the host-larva. It is superiority 
in size and strength that wins the victory in the case of this 
parasite. At the time of the attack the parasite was usually de- 
cidedly smaller than the host. In one instance (nest found at 
Cedar Lake, Washington Co., July 24), the host was at least four 
times as large as the parasite, and still the latter seized the host 
behind the head, and held on as successfully as any of the larger 
ones. In this case, after the parasite had been allowed to suck 
for a few minutes a slender pin was passed between the head of 
the parasite and the body of the victim, and the former forced 
to release its hold. This was done for the purpose of witnessing 
the effects of the bite, as also the subsequent behaviour of host 
and parasite. The host-larva withdrew the front part of its body 
by unsteady, swaying motions (similar to a human being in a 
dazed condition) but it gradually resumed its former position on 
the bee-bread. A small drop of yellowish fluid oozing from the 
skin behind the head indicated the point of attack. Before long 
it again came into dangerous proximity to the parasite, where- 
upon the latter by a quick motion regained its hold in nearly the 
same spot as before. The host-larva made some lively attempts 
to get rid of the aggressor, but undertook nothing in the way of 
a counter attack. 
Whenever two larvae of the parasitic bee Stelis sexmaculata 
are brought together in the same cell they begin hostilities as 
soon as' they come in contact with each other. The one that 
secures the first hold survives, and the victim is subjected to the 
same treatment as the larva of the host-bee. 
The behaviour of the larvae of host-bees when brought in 
contact with each other in the same cell differs greatly from that 
of the larvae of parasitic bees. I have experimented along: this 
line with the larvae of several species of host-bees, and have not 
yet seen one of the larvae injured by its neighbor, although un- 
7. A. Davidson. Entomological News, Vol. 7, p. 316 (Sept., 1S96). 
