1916] The Sleep of Bisects 239 



how safety would be increased by either their aggregation or 

 isolation; if the insects' color and weapon prove sufficient pro- 

 tection for it through its solitary life by day while its enemies 

 are alert, I do not see why it should need further provision for 

 protection at night. Hence the question of the cause or purpose 

 of this imperfect gregariousness still remains open, and even 

 more important than this is the problem again of whether this 

 tendency is ascendant or declining. We may have here the 

 opportunity for a study of the rise of instincts; if so, it will be 

 worth long observation and careful treatment. 



Priononyx thomae Fabr. [vS. A. Rohwer]. 



June 8, 1915, this wasp was asleep on the top of a weed about 

 four feet high on a northern slope of a hill. After being handled 

 rather roughly it eventually roused itself enough to walk when 

 prodded, feebly dragging one foot after the other, but it could 

 not summon enough energy to resume normal activity. 



Another was found July 22, at 7:15 p. m. on the top of a 

 dried plant on a hilltop, and a third was clinging to a sweet- 

 clover stalk on a gloomy September evening. 



Chlorion (Protosphex) ichneumonidae [S. A. Rohwer]. 



One July evening at 7:35 when it was almost dark I came 

 upon a sand- wasp at rest, apparently ready to retire for the 

 night. It sometimes turned its body languidly about and 

 occasionally cleaned its face and antennae, and once it cleaned 

 its wings by thrusting its abdomen above them and rubbing 

 them down. 



Two months later, on a gloomy September morning at 

 8 o'clock, a female sand-wasp was found still asleep on a stink- 

 weed, rather inconspicuous among the fine-cut foliage. 



Bembex nubilipennis Cress. [S. A. Rohwer]. 



These wasps who work so intensely at digging their holes in 

 the earth during the day find shelter in the same hole at night, 

 at least the females do; we have never been able to locate the 

 males' whereabouts at night. It seems the wasp uses her hole 

 in whatever condition it may be, finished or unfinished. At 

 the approach of twilight she creeps into her burrow and from 

 inside she throws up a loose mound of earth to cover the open- 

 ing. In the morning, when the sun is high enough to begin, to 



