1920.] 201 



I went to the same pit hopintj^ to Hiul M. hj-rr/cnJh's at lavpjo, hut tlionn-li 

 31. 2>roscarahaei(s was plentiful cnoiigh, I could find no trace of the 

 rarer species. The cells of various Hjmenoptera were found in the face 

 of the pit, but of these by far the most abundant was CoJIetes daviesnna 

 Sm. I collected and brought home a small l)oxful, perhaps fifty or sixty 

 ceils of the Collctes, as well as a few other cells, Dipterous puparia, etc., 

 found in association with them. As far as M. hrevicollis was concerned, 

 nota trace of it was found, but a number of other insects have since emerged. 

 The CoJJetes cells wei'e sometimes found singly, sometimes in short 

 chains of 2 or 3. Tlie cell itself consists of a thin, more or less trans- 

 parent, white membrane, but is thickly plastered on the inside with the 

 yellowish remains of the pollen, etc., stored up for the bee larva, so that 

 the inhabitant is quite invisible unless the cell be broken open. But 

 above the cell, or above the last of a chain of cells, is frequently found a 

 mass of the white tissue without any pollen inside it, and in this were 

 frequently one or more small white Hymenopterous larvae, apparently 

 not contained in an}' cocoon of their own. In due time these larvae 

 pupated, and about the end of June produced two species of JProsoj^i/'s, 

 viz., P. communis Nyl. and P. l)yalinata Sm. Saunders says of the 

 bees of this genus Ihat they general^ form their nests in bramble-stems, 

 but occasionally utilize holes in walls or posts, and it is possible that in 

 this case they were merely utilizing the burrows of the CoUetes, and had 

 laid up their own food-store in them. No remains of such food-stores 

 were found, and the larvae did not appear to have their own cells. The 

 precise nature of the association between the Colletes and the Prosoj^is 

 appears to require further investigation. 



At the same time or a little later, the Colletes bees made their 

 appearance, but from some of the cells, instead of the legitimate o\mer, 

 appeared the fly Bomhylius minor L. The Somiylius pupa breaks its 

 ^\•AJ completely out of the Colletes cell, and in nature would probably 

 ascend to the surface of the ground, i. e., the face of the pit, and partly 

 project before the fly emerges. Empty pupa-cases of another species^ 

 jB. discolor Mik, were so found in another part of the same pit (host 

 not ascertained). In my boxes, the Bombyliits pupae, having escaped, 

 from the bee-cells, were simply loose in the box, so that the emerging 

 fl}', having no firm purchase when withdrawing its wings from the pupa- 

 sheath, was unable to expand them properly, the tips being more or less 

 shrivelled and ci-ippled. Dr. Perkins's observation of B. minor as a 

 parasite of Andrena clarJcella (Trans. Ent. Soc. Loud. 1919, p. 22S, 

 note) should refer to B. major., while the B. major there noted should be 

 B. discolor (Dr. Perkins has kindly sent me these flies to enable 



