68 SPOLTA ZEYLANICA, 



ON THE NESTING HABITS OF TRYPOXYLON INTRUDENS 

 AND STIGMUS NIGER. 



By E. Ernest Green, F.E.S. 



nnWO species of Trypoxylon occur in Ceylon — T. pileatum, 

 -*- Smith, and T. intrudens^ Smith.* The latter is very common 

 in the Kandy District. Its specific name is an apt one, for this 

 little wasp is continually prying into any crack or cranny in 

 search of a suitable nesting ground. An old nail hole, the hollow 

 shaft of a key, or the stem of a disused tobacco pipe is frequently 

 chosen for the purpose. Occasionally the vacated tunnel of 

 another wasp, e.g., Stigmus, is occupied. Another favourite position 

 is a crevice between the covers or pages of a book ; and a piece of 

 corrugated cardboard is an irresistible attraction. This habit has 

 enabled me to set a neat trap for the insect. By inserting pieces 

 of narrow glass tubing (with aperture of about 4 mm.) in the 

 corrugations of the cardboard I have induced the wasps to 

 build in a glass house, which allowed me to watch their develop- 

 ment from egg to imago. Fig. 2 represents a piece of glass 

 tubing fully occupied by cells showing the insects in various 

 successive stages of development. The partitions between the 

 cells are composed of earthy matter. At the bottom of each cell a 

 small yellowish-white elongate egg is first deposited. The cell is 

 then provisioned with a number of paralyzed spiders sufficient for 

 the needs of a single larva. In the nest under observation the 

 spiders were all of one species — a small black Attid that frequents 

 my room. I have noticed that the lower cells of the series are 

 usually more fully provisioned than those nearer the upper ex- 

 tremity. The occupants of these lower (earlier constructed) cells 

 almost invariably produce female insects, which have a slightly 

 longer larval period. This would appear to be a provision for 

 reducing the difference in the time of emergence between the elder 

 and younger members of the same brood. In spite of this, the occu- 

 pants of the earlier cells complete their transformations much 

 sooner than those at the other end of the series, but must wait 



' 'trypoxylon intruderis, Smith, Trans. Zool. Soc, VII., 1872, p. 188. Bingham, 

 Faun, lirit. Ind., Hymenoptera, vol. I., p. 224. 



