WHEELER— THE PARASITIC ACULEATA. 7 



These very similar observations of Verhoeff, Hoppner and 

 Graenicher on three very different genera of parasitic bees cast 

 some doubt on the older and more meager observations which led 

 Schmiedeknecht and Sharp to assume that the parasitic bee larva 

 is merely a commensal that feeds so voraciously and grows so fast 

 that it compels the host larva to perish from starvation. It was 

 this assumption which led the earlier writers to call the parasites 

 "cuckoo bees." It is possible, of course, that some parasites, e. g., 

 Noniada, which infests the nests of Andrcna and Halictus, may 

 conform to this older view, but renewed investigation is certainly 

 demanded by the results of the authors I have been considering. 



Graenicher (1906) has also made some valuable observations 

 which show that vision as well as odor is an important factor in 

 the parasitic bee's method of locating the nest of the host. Speak- 

 ing of Argyrosclenis minima, which is a parasite of Collctcs eiiloplii, 

 he says : 



" It is quite evident that after having discovered the nest this parasitic 

 bee pursued a course similar to that of a host-bee when constructing a nest. 

 It started out to make a careful and repeated inspection of the environment 

 of the nest, gradually covering more territory in different directions, but 

 often returning to the nest as the main object of its attention. Being pos- 

 sessed of a good memory for visual impressions it became acquainted with 

 the locality within 6 minutes, and experienced no difficulty in refinding the 

 nest at its next visit after an absence of 14 minutes. It gradually acquired 

 a thorough familiarity with the topography of the region, and on its return 

 to the nest it was seen to fly towards the opening as directly as the owner 

 itself. 



" Such a parasitic bee when hunting for a nest of a host-bee is not always 

 flying around in a haphazard way, trusting to its good luck in finding a nest 

 here today, and one somewhere else tomorrow. When it has come across a 

 suitable one it is very careful to keep this under observation, and in making 

 its trips to and away from the nest it is directed by its visual memory in 

 exactly the same manner as the host-bee itself. It would not be in the inter- 

 est of such a bee to pursue a different course. The work of the host-bee in 

 constructing a cell, and provisioning it with the food-supply must have pro- 

 gressed to a certain point before the parasitic bee may find it suitable for the 

 reception of the latter's egg. For this reason such a bee has to make re- 

 peated visits to the nest, in order to be on hand when the right time comes. 

 If it were in the habit of wandering around until it happened to come across 

 a host-bee's cell in the proper stage of construction, then it might not get 

 much chance to deposit an egg within its life-time of a few weeks duration, 

 especially in rainy seasons. It is even possible that a parasitic bee has more 

 than one nest under observation during the same period." 



