BURGLARS 291 



the whole there can be no doubt that their pre- 

 vailing habit is to have their young brought up at 

 the expense of the burrowing bees Andrena and 

 Halictus. 



A more remarkable case is that of the Humble 

 Bees {Bombus) and the Cuckoo Bees {Psithyrus). 

 Here the two tribes are so much alike in size, 

 clothing, and colouring that only an expert can tell 

 you which is which. But if one examines the 

 hind legs of the two the difference is at once 

 manifest in the presence and absence of the pollen- 

 basket respectively. It was formerly thought that 

 these Cuckoo Bees — of which we have five species — 

 were merely messmates of the Humble Bees, in 

 some way making return for their food and lodging ; 

 but there can be no doubt that they are actual 

 parasites, thriving at the Humble Bee's expense, 

 and bringing about the deterioration or absolute 

 ruin of the colony. 



The Cuckoo Bees are all males and females : 

 there is no worker class. Each species in colour 

 mimics that species of Humble Bee upon which it 

 preys, but is usually somewhat larger. Why there 

 should be this mimicry is not clear, for it does not 

 impose upon the Humble Bee. The mother of 

 the colony detects the cheat, and in some species 

 attempts to eject the intruder. But this appears 

 always to result in the Humble Bee being killed, 

 and the progress of the colony being checked, of 

 course. This is apparently the Cuckoo's object. 

 She helps herself to the contents of the honey-pot, 



