GUESTS AND PARASITES OF HALICTUS. 



I I 



jection to the free entrance of visitors of the other sex, as has 

 been shown by the Peckhams.' Mutilla canadensis appears to 

 be the most dreaded enemy, as it alone is noticed by the 

 bees. With a little reasoning ability many of the other parasites 

 could be readily annihilated, whereas no move is made for pro- 

 tection against these foes except by the guard at the door. But 

 how are the bees to know, even in the case of Mutilla, that their 

 guests mean harm to their progeny ? Probably they do not in a 

 strict sense. It is evident, however, that the instinct of guarding 

 the entrance to the nest could have been developed through the 



Fig. 6. Stethopathiis occidentalism sp. nov., lateral view. 



action of natural selection of favorable variations in habit, while it 

 would be difficult to derive a number of specific reactions towards 

 the different guests in the same manner. The very commonness 

 of Mutilla and its conspicuous size are probably the reason that 

 a specific reaction has been developed in this single case. 

 Halictns is far less sensitive to its surroundings than manj' of 

 the fossorial wasps are, coming and going even though we dis- 



1 " Instincts and Habits of the Solitary Wasps," p. 79, 1897. 



