4 MELANDER AND BRUES. 



males, who sit at the doorway, their rounded heads neatly filling 

 out the entrance. When the female returns pollen-laden, the 

 little guard slips into the first side passage while she enters, and 

 then as quickly returns to his post. The incomers are perceived 

 at a distance of half a foot, probably announced by the buzzing 

 of their wings. Even when the little watchers can not see the 

 female coming they dart half way out of their retreat at her ap- 

 proach. With antennae vibrating and mandibles spread the males 

 either manifest a joyful greeting for their nest-mates or show an 



FIG. 2. Nest of Halictus near Austin, Texas. 



equal degree of hostility towards any stranger that may venture 

 too near. 



The most dreaded of the enemies of the Halicti is perhaps the 

 little velvet ant, Mutilla canadensis Blake, which is common 

 nearly everywhere in North America, running about on the nests 

 of these bees, its distribution practically coinciding with that of 

 this species. Perhaps it is the stridulation produced by the ab- 

 domen of these intruders that arouses the ire of the guard at the 

 door, for no sooner does one approach a nest than the watcher, 

 if it be a female, rushes out and pounces upon the JMutilla, en- 

 deavoring to sting it to death. Down the hill-slope they roll, 

 heedless of everything but an inborn desire to annihilate each 



