226 A YEAR OF COSTA RICAN NATURAL HISTORY 



chim," which we supposed to have come from this nest. 

 After our return to Philadelphia we took a dead wasp out 

 of one of the cells, similar in size, shape and color pattern to 

 that of May i6 but with yellow replacing the red. Both of 

 these wasps had a long slender waist and belong to the 

 species Zethus histrionicus, of the potter wasp family. The 

 black and yellow one, which certainly came from this nest, 

 closely resembles in size, shape, colors and pattern the social 

 wasp Polybia fasciata, which we obtained in March at Cachi. 

 Zethus is a solitary wasp, that is, there is no cooperation 

 among the adults in building their nests or caring for their 

 young. It is a curious fact that, among the true wasps 

 (those whose fore wings are folded lengthwise) the solitary 

 or social habit appears to be correlated with a structural 

 peculiarity whose relation to these habits is still unper- 

 ceived. In the solitary forms the claws terminating each 

 leg have a tooth before the tip, which does not exist in the 

 social species. We know that certain small parts of the 

 legs of the honey bee perform certain definite functions and 

 it may be that more intensive future study of the habits 

 and modes of work of wasps will show that these teeth have 

 a definite relation to the development or non-development 

 of social life. But for the present, these anatomical details 

 are merely convenient indexes to the nature of the lives of 

 these industrious little artificers. In addition to this differ- 

 ence in the claws which distinguishes the Vespidae (social) 

 from the Eumenidse (potter wasps, solitary), our Zethus has 

 relatively coarse punctures over much of the body, which 

 are absent or but feebly developed in Polybia fasciata. 



In March an immense paper-wasps' nest, high up in a 

 rather isolated tree near the Reventazon bridge, harbored an 

 active colony. It was as large as a man's body, balloon- 

 shaped and with an opening below through which the in- 

 sects were entering and leaving. 



