1916] The Sleep of Insects 255 



them to waken and shift their position. The helplessness of the 

 drowsy butterflies when thrown up into the breeze, and the fact 

 that about half of them tried but failed to go against the wind 

 would lead us to conclude that this habitual position is the result 

 merely of mechanical force upon the languid insects. 



Minot points out that the allied species, Colias philodice and 

 Pieris rapae, begin to alight on the grass and before twilight is 

 ended they creep down to the roots of the grass-stalks and there 

 spend the night in sleep. The difference in habits of those and 

 our species may be due to meteorological conditions. Minot's 

 observations were probably made at Boston, where the temper- 

 ature and the breezes would probably be more trying in unpro- 

 tected spots than at St.. Loius. 



Pieris rapae Linn. 



At 8:30 p. m. on August 17 this white butterfly was asleep 

 on a pig-weed, sitting on the top of a leaf. 



Nathalis iole, Boisduval [G. T. Hosenfelt]. 



At dusk during the early days of September hundreds of 

 these little yellow butterflies may be found at rest or asleep on 

 the grass or on the low twigs of weeds. If one walks through the 

 vegetation while it is still light, they fly up in great numbers; 

 if one attempts to take them he will have difficulty in doing 

 so for they fly away without much provocation. But as dark- 

 ness falls they become lethargic and may be picked up like 

 blossoms. 



They show to some extent the same anemotropism as do 

 P. protodice; they always creep down to a sheltered twig near 

 the ground, quite ignoring the many taller plants, as iron- weed, 

 and snakeroot, which abound near by. 



Phyciodes tharos Drury [G. T. Hosenfelt]. 



We have a number of records of this species, noted during 

 August and September, and each case differs from the others. 

 Two were found asleep at 10 o'clock in a vertical position on the 

 twigs of a dead willow five feet from the ground; another rested 

 horizontally on the low branches of a cocklebur; another was 

 found drowsily feeding at twilight on the disk florets of a sun- 

 flower, and still others were on the ground and on the tops of 

 iron- weeds. They became drowsy and sluggish in the early 



