ON THE OCCURRENCE OF MICRODON MUTABILIS. 43 



the Diptera to which Microdon belongs — the Syr- 

 phidce — feed ckiring their larval existence on plant- 

 lice ; and as the black ant keeps aphides in its nest 

 it is possible that the Dipteron may feed on them ; 

 but if so, it is certainly very curious that the ants 

 would tolerate their presence in the nest, as they 

 are very careful in looking after their aphides, on 

 the excrement of which they feed. Poujade even 

 suggests that they may feed on the ant larvae, but 

 the same objection as that urged against their 

 feeding on the aphides applies equally well here. 



