54O HYMENOPTERA CHAP. 



and Aphididae, and some deposit their eggs in the egg-cases of 

 Blattidae. The details of the life-history are well known in 

 only a few cases. 



The career of Leucospis gigas has been investigated by Fabre, 

 and exhibits a very remarkable form of hypermetamorphosis. 1 



This Insect is of comparatively 

 large size and of vivid colours, 

 wasp-like, black contrasting with 

 yellow, as in the case of the 

 wasps ; and like these it has the 

 wings folded or doubled. The 

 female bears a long ovipositor, 

 which by a peculiar modification 

 FIG. 35Q.Leucospis gigas, female. is packed in a groove on the 



back of the Insect. This species 



lives in Southern Europe at the expense of Chalicodoma muraria, 

 a mason-bee that forms cells of a hard cement for its nest, the 

 cells being placed together in masses of considerable size ; each cell 

 contains, or rather should contain, a larva of the bee, and is closed 

 by masonry, in the construction of which the bee displays much 

 ability. It is the mission of the Leucospis to penetrate the 

 masonry by means of its ovipositor, and to deposit an egg in the 

 cell of the bee. The period chosen for this predatory attack is 

 the end of July or the beginning of August, at which time the 

 bee-larva is in the torpid and powerless condition that precedes 

 its assumption of the pupal state. The Leucospis, walking about 

 leisurely and circumspectly on the masonry of the nest, tests it 

 repeatedly by touching with the tips of the antennae, for it is 

 most important that a proper spot should be selected. The bee's 

 cell is placed in a mass of solid niasonry, a considerable part 

 but a part only of whose area is occupied by the group of cells ; 

 every cell is closed by hard mortar, making an uneven surface, 

 and the face of the masonry is rendered more even by a layer of 

 hardened clay outside the rougher material ; it is the task of the 

 Leucospis to detect a suitable spot, in the apparently uniform 

 external covering, and there to effect the penetration so as to 

 introduce an egg into a cell. By what sensations the fly may 

 be guided is unknown. After a spot has been selected and the 

 ovipositor brought into play, the masonry is ultimately pierced 

 1 Souvenirs entomologiqucs. Troisieme serie, 1886, p. 155. 



