130 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. r,£ 



is quite possible that the above observations may refer to one of 

 these. 



On leavmg the nest the entrance is invariably closed. The 

 rapidity with which the wasp secures flies is showai by the following 

 record of intervals between visits to the nest on each of which a fly 

 was brought in. With wasp No. 29 observations began with the 

 visit at 11.18 a. m., and closed with the visit at 12.30 p. m. The 

 successive intervals betw^een visits were 5, 4, 12, 14, 5h, llj, 3^, 11^, 

 and 5 minutes. In the case of No. 37 the intervals, beginning at 9.32 

 a.m. and closing at 11.02 a. m., were as follows: 5,4, 6, 3, 5, 6, 14, 18, 5, 

 and 24 minutes. These two cases may be taken as fairly representing 

 the energy wdth which the wasp goes about her task. In each of 

 these nests the larva was nearing maturity. 



As soon as the larva ceases feedmg it encases itself in a cell or 

 cocoon composed of grains of sand entangled in meshes of silk and 

 firmly cemented together by a hard, tough substance probably fur- 

 nished from glands in the mouth. When it begins to form its cocoon 

 the larva spms a loose felt-work of silk about it as a foundation for 

 the formation of the cocoon proper. In one case this silken felt-w^ork 

 was attached to the under surface of the glass covering the breeding 

 ceU, so that the cocoon formed within it was held above the sand in 

 the cell and was firmly cemented to the underside of the glass. 

 Although this larva was not surrounded on aJl sides by sand, as is the 

 case when the cocoon is formed in the nest, nevertheless, by some 

 means that were not observed, it succeeded in incorporatmg grains 

 of sand in the wall of the cocoon. 



Two cases coming under my observation throw new light upon 

 the life-history of B. spinolae. In the fii-st (No. 37) the nest was 

 constructed and the egg deposited late in the afternoon of June 27, 

 the nest was marked and kept under observation until July 3, when 

 the mother wasp w^as captured and the nest digged up. The larva 

 therein was nearly full grown. I placed it in a breedmg cell together 

 with the flies found in the brood chamber with it. On July 4 I gave 

 it an additional supply of house-fhes and on the morning of July 5 

 it had begun the formation of its cocoon. The larva was covered at 

 once with sand and the cocoon was complete on July 6. This cell 

 with its contents was then set aside and not inspected again until 

 August 24, when to my surprise I found the adult wasp had emerged 

 and miable to escape had perished in the cell. The date of its emer- 

 gence is not definitely known. In the second case (No. 48) the egg 

 was laid July 10 and hatched on July 12. The larva began forming 

 its cocoon on the afternoon of July 17 and completed it on July 18. 

 It was this wasp that formed its cocoon without being covered with 

 sand. This cell was also set aside, but after the discovery related 

 above it was closely watched and the adult wasp emerged on Septem- 

 ber 2. Thus this wasp completed its transformations from egg to 



