The Bumble-Bee Fly 



not to hustle the passers-by, she can dab her 

 eggs, without danger, on the paper wall. No 

 one will know of her presence. The danger- 

 ous thing is to cross the threshold of the bur- 

 row in broad daylight, before the eyes of those 

 who go in and out. At that moment alone, 

 protective mimicry would be convenient. Now 

 does the entrance of the Volucella into the 

 presence of a few Wasps entail such very 

 great risks? The Wasps' nest in my enclosure, 

 the one which was afterwards to perish in the 

 sun under a bell-glass, gave me the opportunity 

 for prolonged observations, but without any 

 result upon the subject of my immediate con- 

 cern. The Bumble-bee Fly did not appear. 

 The period for her visits had doubtless passed ; 

 for I found plenty of her grubs when the nest 

 was dug up. 



Other flies rewarded me for my assiduity. 

 I saw some — at a respectful distance, I need 

 hardly say — entering the burrow. They were 

 insignificant in size and of a dark-grey colour, 

 not unlike that of the House-fly. They had 

 not a patch of yellow about them and cer- 

 tainly had no claim to protective mimicry. 

 Nevertheless, they went in and out as they 

 pleased, calmly, as though they were at home. 



As long as there was not too great a number 



261 



