522 ANNUAL, REPORT SMITHSONIA'N INSTITUTION, 1910. 



frequently found in S. comnta. One may be permitted to see in 

 these aggregations the begimiings of association in colonies, such 

 as different authors have observed; for example, in Pollstes (Mar- 

 chal, 1900; Ferton, 1901). It is difficult to say whether these asso- 

 ciations are purely and entirely due to chance ; whether the different 

 grouped nests are made by individuals which are strangers to one 

 another ; or whether they are not rather made by individuals from a 

 single nest which build their cells in proximity to those in which they 

 are born. If this hypothesis has not yet been directly verified, it has 

 at least the appearance of great probability. One may advance in 

 its favor the instinct of knowledge of places which leads the males of 

 S. cornuta, for example, to return frequently to the same nests and 

 watch them closely. It may be asked why it is not the same as re- 

 gards the females, and whether they may not possess some tendencies 

 to build by preference in the vicinity of the nests in which they were 

 born. We firmly believe that such is the fact, and that certain of 

 these associations may be interpreted as the fii-st step in the evolution 

 of the instincts of the solitary wasps in the direction of those of the 

 social wasps. 



Parasites of Synagris. — The nests of Synagris may be invaded by 

 different insects, some merely commensals which use only the cells 

 of old nests in which in their turn to rear their young; others, genu- 

 ine enemies that seek the larvae of Synagns in order tO' prey on 

 them. The usual commensals of the nests of Syruigris are sometimes 

 solitary bees of the genera 3IegacMle, Osmia, etc. ; sometimes spider- 

 wasps (Pompilidse). The majorit}- of old nests are occupied by 

 these hymenoptera, sometimes isolated, sometimes associated in the 

 same nest. Occasionally the nest of the spider-wasps is made on the 

 cells previously occupied by the solitary bees. 



One of the most formidable parasites of Synagris is an ichneumon- 

 fly, Osprynchotus iiavipes Brulle. This insect has a wide distribu- 

 tion in Africa. The Museum of Paris contains specimens of it from 

 Dakar, Casamance, Mozambique, British East Africa, the Gaboon, 

 and the valley of the Zambezi. The larvae of this ichneumon-fly 

 (pi. 4, fig. 2) infest those of several species of Synagris. I have ob- 

 tained them from S. comuta and S. sicheliana. It is probable that 

 they attack all the species. We have called attention above to the 

 disastrous effects as regards the development of the whole of the 

 later progeny of the wasps, due to the attack of Osprynchotus on 

 the first larva in a nest of S. comuta. The great retardation which 

 resulted in the development of the parasitized larva delayed the 

 building of new cells and prevented the mother wasp, which was 

 entirely devoted to her fated offspring, from rearing new larvae, 

 that might perhaps have escaped the parasite. Thus, the very per- 



