130 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 52. 



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

 these. 



On leaving the nest the entrance is invariably closed. The 

 rapidity with which the wasp secures flies is shown 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 between visits were 5, 4, 12, 14, 5 J, 11 J, 3J, Hi, 

 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 with which the wasp goes about her task. In each of 

 these nests the larva was nearing maturity. 



As soon as the larva ceases feeding 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 spins a loose felt-work of silk about it as a foundation for 

 the f ormation of the cocoon proper. In one case this silken felt-work 

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

 cell, 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 all 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 incorporating 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 first (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 was captured and the nest digged up. The larva 

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

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

 it an additional supply of house-flies 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 unable 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 



