136 H. von Ihering on the 



of the Old-World Vespa is the only one that builds a compli- 

 cated nest surrounded by an envelope : all the rest in their 

 style of architecture more or less resemble Polistes. In eastern 

 South America, on the other hand, what wealth and variety 

 of structural types, what elegance and marvellous, artistic 

 skill ! While referring the reader to Saussure's classical 

 monograph, I would here draw attention only to what is new 

 among my observations. 



It is well-known that the nest of Mischocyttarus is very 

 similar in construction to that of Polistes, differing only in 

 the longer central pedicle ; but it was to me an altogether 

 surprising and unexpected discovery to rind that there are also 

 species of Polybia whose nests are indistinguishable from 

 those of PoNsies. The species in question are Polybia vicina, 

 Sauss., and P. ignobilia, Halid. All the other members of 

 the genus, even PoJybia atra, Sauss., build nests with con- 

 centric envelopes, so that when the nest is enlarged the last 

 and most recent envelope is always used as a base for the 

 new combs. It may appear at first sight to be a matter of no 

 special importance that within the limits of a large genus a 

 portion of the species should differ in the structure of their 

 nests ; but the subject is nevertheless a much more compli- 

 cated one, since with these differences others in the mode of 

 life of the communities are directly connected. In the one 

 group we have the foundation by a fertilized female of what 

 is usually a community existing for one year, in the other 

 long-lived colonies founded by the formation of swarms, as in 

 the case of bees. 



I am bound to admit that I regard these species of Polybia 

 which live after the manner of Polistes as representing a 

 distinct genus. It is probably not customary to utilize biolo- 

 gical considerations for the foundation of genera, but perhaps 

 even in this case closer investigation will demonstrate the 

 morphological basis for the separation inferred on biological 

 grounds. 



According to their mode of life, or, say, the formation of 

 communities, the social wasps of South America may there- 

 fore be divided into two groups : — 



(1) Summer communities, or such as last for one year, 

 founded in spring by fertilized females which have hibernated : 

 Polistes, Mischocyttarus, and Pseudopolybia (a name which 

 1 adopt for Pulybia-\\kQ wasps that construct nests after the 

 manner of Polisleti). 



(2) Perennial communities, founded by swarms after the 

 fashion of bee-colonies : Polybia, Apoica, Tatua, Synoeca, 

 Chartergus, Nectar inia. 



