1916] The Sleep of Insects 231 



and where does mating occur, and is more than one union 

 necessary? 



Has this gregarious habit been acquired as a means of pro- 

 tection and mutual guarding, since the sting of this insect is 

 very mild? 



Sceliphron (Pelopoeus) caBmentarium. 



Even in localities where 5". caementariiim, the common mud- 

 daubers, occur in abundance, I have only once been able to 

 discover how they sleep and where they spend their nights, 

 since they do not remain on their nests after working hours. 

 During the summer of 1915, from June 1 to 5, two mud-daubers 

 returned each night to two distinct elderberry bushes, and while 

 they did not always take the same branch they usually occupied 

 each the same plant. Night after night I watched them until 

 nearly dark, and found that as it became darker they grew quiet 

 and so remained, resting on the foliage in an easy but not 

 exaggerated posture. 



One day late in May it suddenly became cloudy and quite 

 dark at mid-day, and a few drops of rain fell. At this time I 

 discovered eight Sceliphron on the elderberry bushes, intently 

 walking up and down the stems. In a few minutes the sun 

 shone brightly again and they flew away. I watched the 

 bushes for their return, but they did not appear. Soon after 

 that another cloud darkened the sky, and four wasps promptly 

 reappeared. They walked about nervously on the stems, and 

 w-hen the rain fell fast they all flew away, probably to better 

 shelter. They may have been only seeking prey; if they were 

 really seeking shelter, they certainly would have found better 

 at their nesting-sites. 



On several evenings some of these wasps accompanied 

 Sphex {Ammophila) pictipennis to their regular sleeping places 

 on the elderberry bushes, but each time they soon wandered 

 elsewhere, (see p. 231). 



Sphex (Ammophila) pictipennis Walsh [S. A. Rohwer].* 

 In my. garden are three elderberry bushes fifteen feet apart. 

 At this particular stage of growth they all bore unripe berries. 

 I mention these facts in detail because while the plant was com- 

 paratively abundant in the vicinity it was on one bush, the 



*Followmg the suggestion of Dr. Cockerell in the Ent. News, we place in 

 brackets the name of the gentleman who kindly identified the species for us. 



