298 Mr Warburton, Note on the solitary wasp, 



might very well be wasp No. 2. Anyhow it entered the burrow, 

 and by 7.50 it had turned out more "sawdust" containing several 

 of the flies so carefully stored up by wasp No. 1 ! The explanation 

 that first occurred to one was that the wasp wanted to dig, and 

 naturally found it easier to work w^here someone had been before. 

 Such a defective instinct would, however, militate against the 

 preservation of the race. Moreover there were no further develop- 

 ments, and No. 2 remained satisfied with undoing some of No. I's 

 work. A wild suggestion did occur to me, which I will give for 

 what it is worth. Is it possible that one of those working from the 

 interior became aware of operations from the outside which might 

 imperil the results of its own labours, and proceeded to put a 

 stop to them? 



With regard to the remaining wasps, which entered by the 

 woodpecker's hole and worked from the inside, the following notes 

 may be given. 



The earlier hasty inspections of the interior showed that the 

 cavity of the woodpecker's nest was being gradually filled with the 

 "sawdust" of their workings, and conspicuous on the "sawdust" 

 were a number of Syrphid flies, apparently dead. At the final 

 investigation at the beginning of October about a hundred and 

 twenty of these derelict flies were found in the central cavity, and 

 as there were certainly not more than six wasps at work at any 

 time, and as two were early captured and retained for identification, 

 it is probably safe to estimate the average numbers of the wasps 

 responsible for discarding them at five. This allows twenty-four 

 discarded flies to each wasp — about six hours strenuous labour by 

 each insect entirely wasted! As wasp No. 1 was never seen to 

 discard a captured fly this phenomenon was apparently attributable 

 to the conditions prevailing inside. There all the burrows com- 

 menced with a horizontal boring at the junction of the two sections 

 of the log, at some little distance from the main opening. After 

 alighting at the main entrance they had, therefore, either to fly 

 across or to crawl round the central cavity, and it seems as though 

 a number of flies had been accidentally dropped. It would be 

 quite in keeping with what has been observed in the case of allied 

 insects that a wasp which had accidentally dropped a fly should 

 make no attempt to retrieve it, but should simply go away and 

 catch another. These discarded flies were in any case very useful 

 as evidence of the particular prey selected by Crabro cephalotes. 



At the beginning of October some of these flies had been 

 reduced to fragments by other predaceous creatures, but of 113 

 recognisable specimens 60 were S. halteatus. 



My friend Mr N. D, F. Pearce very kindly undertook to identify 

 the remainder for me and he finds among them five species of 

 Syrphus, three of Platychirus, two of Melanostoma, and one of 



