i6 THE SCOTTISH NATURALIST 



the fly maggots burrowed into the sand to avoid the h'ght. 

 I then made two little pits in the sand as far as possible 

 from where the maggot had disappeared. In one pit I placed 

 a pollen ball and in the other a bee grub. Invariably the 

 maggots found the pollen ball and ate it, totally neglecting the 

 bee grub, which itself was too helpless to find the pollen ball. 

 This experiment was repeated many times with fly maggots, 

 each placed in a separate box with a pollen ball and a 

 bee grub. Eventually all these maggots became full fed and 

 pupated. This proves that the food of the fly maggot is the 

 stored pollen and that this larva can complete its entire 

 growth on this diet. I have one record that seems to show 

 that if supplied with insufficient pollen paste the maggots 

 would eat bee grubs. A small fly larva, and a young bee 

 ■grub were placed in a pill box along with two portions of a 

 pollen ball which quickly became mouldy. The bee grub 

 ceased to eat. The fly maggot first devoured all the pollen 

 food, and then attacked the bee grub. 



I never found a maggot eating a bee grub in the brood 

 chamber and never saw any remains of a bee grub that had 

 been eaten. Neither did I ever find both a maggot and a 

 bee grub present in the same brood chamber. That the 

 main food of the maggot is the pollen ball is beyond doubt. 

 I do not wish to convey the impression that a large propor- 

 tion of bees' nests contain maggots. Only a small proportion 

 were thus parasitised, a much smaller proportion than might 

 be expected from the activities of the female fly. Incident- 

 ally I may remark that fungus proves a formidable enemy of 

 both bee and fly larvae. On many occasions, especially in the 

 wet and warm first fortnight of last July, it was common to 

 find larvae and pupae of Andrena and larvae oi Hyleniyia, and 

 the pollen ball also, enveloped in mycelium; as the fungus was 

 not found in the spore stage I am not able to say the species. 



After an absence of some weeks I revisited the bee 

 colonies towards the end of August, No flies were to be 

 seen, and in the bees' nests all stores of pollen had been 

 devoured. The full-fed bee grubs were lying ready for 

 hibernation, while most of the dipterous larva? had already 

 pupated. 



