Drone-Flies. 



273 



and chrysalids of the humble-bees is an erroneous one, it may be stated that attempts 

 have been made to bring up the fly-grubs on sueh a diet, but they preferred to 

 starve rather than attack hving Insects ; though on being presentecl witli dead 

 bee-chrysalids they eagerly availed themselves of such food, showing that their 

 mission is to prevent putrefaction and all the horrors that ensue from it. 



Other members of the same genus attach themselves to the service of the social 

 wasps, but the remarkable thing here, in the light of the teleologists' view, is that 

 the species concerned do not resemble wasps, though if the wasps were not convinced 

 of the benevolent intentions of these flies the latter would need protective resemblance 

 far more than the humble-bee fly, for two-winged flies form a large percentage of 

 the food of wasps. One of these flies ^ we have found particularly abundant in the 

 grub stage in the underground nests of one of the common wasps. '^ We have 

 dug out these nests in autumn when the activity of the communitv was practically 



over. .A. few cells alone remained capped, - 1 



showing tliat tlie new wasp had not emerged. 

 ^Ian\' had been newh' \'acated, and in 

 others were dead grubs, which are believed 

 to be killed by the wasps when there are 

 insufficient workers to feed them to matu- 

 rity. The combs, removed to tin boxes 



to sccurt' whatever living associates 



might 



be in or on them, after being closed up 



for a few hours yielded an abominable 



ammoniacal odour from the effete matter 



contained in the cells. These combs had 



hundreds of volucella-grubs creeping over 



them, from the almost full-sized specimens 



three-quarters of an inch long down to 



minute individuals that measured only a 



couple of millimetres, and were apparently 



newiv hatched. Most of them were active. 



Having cleared out all the refuse from one 



cell, a grub would look about for the newt 



one that demanded attention. Standing at 



would be extended to make iiKpiirv as to the condition of the cell, and it 



it was found to have been cleaned out the grub would move on. l)ut it it 



proved to be in (from this grub's point of view) a nice dirty condition, then he would 



get inside and ])ursue his proper avocation. The fully-grown grubs were too large 



to get quite into the largest cells — those that had produced queens — but all that 



was visible was the broad hinder segments forming a dark convex cap to the cell 



with the double breathing organ in tlu> middle. 



The form of this grub will be seen in the photograph. When at rest it is a 

 flattened pear-shape. The ground colour is a (lirl\- white mottled with dark brown. 

 The body is rough with transverse ridges and low spines. Along the centre of the 

 upper side is a row of stouter bushy spines, and along the margin of the back is 



1 Volucella pellucens. » Vcspa germanica. 



/'//-./„ hv] Jl. Main, F.E.S. 



Chrysalis of Drone-Fly. 



Till' f^nib changes to a chrysalis within the grub-skin, 

 so thtic isonlyasHght difference in its outward appear- 

 ance ; l)nt a n"W feature is seen in two short horns near 

 tli<- broad end. These are the breathing organs. Within 

 ttie hardened, spiny grub- skin the white chrysalis shows 

 all the parts of il\e future tly folded close to the body. 



the edge of it, the fore-part 



