302 HYMENOPTERA 



This *' aposematic noise " is entirely in keeping with, 

 and explicable by the same means as, the conspicuous 

 appearance of the insect, which is thus enabled to appeal 

 to more senses than one. But if the Pompilid is con- 

 cealed, then one explanation is required for its colour 

 and another for its noisy flight, though it is difficult to 

 imagine what explanation of the latter could be given. 

 I have suggested elsewhere ^ that there is an analogous 

 example among birds in the case of the large black and 

 white " E'nga-nga " hornbill, whose wings make an extra- 

 ordinary roaring noise as it beats them, or sails with 

 them outspread through the air, often at the same time 

 calling attention to itself by its loud raucous cry. 



It has been mentioned in the case of the Bembecidae 

 that they have enemies in certain flies, and the same 

 holds good with Sphegidae and Pompilidae. 



The golden moment for the enemies of these fossors is 

 when they have arrived with their burden at the mouth 

 of the burrow and leave it outside while they go down. 

 The attendant fly can then dart down and deposit its 

 own egg up'on the prey while the fossor is busy, and that 

 it does so is evidenced by the fact that on grasshoppers 

 taken out of the burrows of the little Sphex marginatus 

 I found dipterous larvae which became flies of a species 

 unknown to the British Museum, but alUed to the Milto- 

 gramma described by Fabre. It is rather interesting 

 that whereas most fossors seem to take little notice of 

 other insects while they are at work, Sphex marginatus 

 is extremely suspicious of any intruders on its privacy, 

 and charges fiercely with open mandibles at even the 

 smallest ant that draws near to its burrow, much to the 

 dismay of the quite inoffensive ant ! If the trespasser 

 does not at once withdraw, the Sphex makes threatening 

 movements as if about to sting, turning the tip of her 

 abdomen forwards between her legs. 



» p. 168. 



