1916] The Sleep of Insects 249 



Sparnopolius brevirostris Macq. [F. Knab]. 



Near a dozen yellow velvety bee-flies were seen at twilight 

 early in September, gracefully resting on various flowers and 

 leaves, but not one could be caught, even by extreme efi'ort, so 

 quick and agile were they. 



While I feel confident that they spend the night in the posi- 

 tion in which one finds them at dusk and they eventually relax 

 in sleep thus, yet they are more active and alert throughout the 

 twilight period than any other insect I have met among the 

 higher, swiftly-moving insects. Only late in the season, when 

 the weather grew chill, could they be taken at the twilight 

 hours when most other insects could easily be picked up. They 

 do not congregate in definite swarms to sleep, but frequently a 

 half dozen or so are seen occupying neighboring ragweed or 

 other plants. 



Argyromoeba obsoletum Loew. [F. Knab]. 



On July 29, two of these bee-flies were seen asleep, one on 

 the under side of an overhanging rock by the Meramec River, 

 and the other on a twig sheltered by a protruding rock by the 

 roadside. It was quite dark and both must surely have been 

 asleep, for neither my bright light nor my hand when I picked 

 them up disturbed them, although they are normally very 

 active Diptera. 



DIL\GON-FLIES. 



Libellula pulchella Dmry. [R. P. Currie]. 



Libellula luctuosa Burm. [R. P. Currie]. 



Anax Junius Drury. [R. P. Currie]. 



Dragon-flies are swift and agile in their flight and are difficult 

 to apprehend during the day, at least those species which are 

 abundant in this vicinity. The sharp contrast between this 

 and their behavior after dusk leaves little doubt that they lapse 

 into deep sleep at night. I have noticed only a few individuals 

 at night, but all of these had chosen for their roost a gray, dead 

 twig among green shrubbery, about five feet from the ground. 

 They rest with the head up, holding on with their feet and 

 automatically clinging tenaceously. After they are soundly 

 asleep, at 7 or 8 o'clock, they are indifferent to a strong light or 

 even to being pulled off their support and handled. 



