SOLITARY WASPS OF GENUS SYNAGRIS ROUBAUD. 521 



affirmed, in my opinion, without hesitation, that this species is bio- 

 logically of the same group as S. cornuta L. 



Evolution of instinct among the solitary wasps. — The biological 

 history of the species of Synagris permits us to see, within the limits 

 of a single genus, instinct developing from the provisioning in mass 

 characteristic of the ordinary type of eumenids to continuous pro- 

 visioning, and finally to the feeding of the larvae from day to day 

 after the mode of the wasps which live in colonies. We find com- 

 bined in a singular manner in the same type of wasps the principal 

 steps which lead from the primitive instinct of the solitary wasps to 

 the much more perfected instinct of the social wasps. 



By reason of the facts which we have brought forward, it should 

 not be thought that the habit of nourishing the larvae from day to 

 day on caterpillars ground into a mass, which is customary among 

 the social wasps, may represent a primitive mode of provisioning 

 peculiar to wasps which do not know how to make use of the sting 

 to paralyze their prey. It is, on the contrary, manifestly a modi- 

 fied form of the instinct of provisioning found among the wasps 

 that paralyze their prey which forms a complete substitute for these 

 hereditary habits, while at the same time maternal attachment and 

 caring for the progeny are developed. 



This conception is a little different from that of Bouvier (1901), 

 who regarded the habits of the social wasps and the solitary wasps 

 as derived from a common source, this source being a species with the 

 habits of Monedula punctata, which kills its prey without paralyzing 

 it and provisions its nest continuously from day to day. Hence, the 

 habits of these wasps are to be regarded as having developed in two 

 different directions, the social wasps preserving the habit of killing 

 their prey and provisioning the nest continuously (with slight modi- 

 fications), the solitary wasps acquiring, on the contrary, with the 

 habit of paralyzing their victims, the possibility of provisioning the 

 nest all at one time. The evolution of instinct in Synagris, which we 

 have been able to follow, leads to different conceptions as regards the 

 wasps. Feeding the young by mouthfuls with caterpillars ground up 

 into a paste represents the last term of an evolution of the rearing 

 instinct the initial form of which is a slow, progressive, and continu- 

 ous provisioning with paralyzed prey, which permits the mother 

 wasp herself to watch the growth of her offspring. 



In the mode of rearing the larva so highly perfected in S. cornuta 

 may be seen the direct bond of union between the solitary wasps and 

 the social wasps. To understand how the final stage of evolution 

 is reached by the latter it is only necessary to observe the colonizing 

 tendencies among the solitary wasps, which employ continuous pro- 

 visioning and nourishing their young by mouthfuls. We have already 

 noted in Synagris sicheliana the association of nests, which is also 



