2 Bulletin American Museum of Natural History. [Vol. XXII I^ 



they indicate with equal force that the causes of polymorphism may be so- 

 recondite as to give little encouragement to the crude physiological methods 

 at present available. In other words, much water will have to flow through 

 the biological mill before we possess sufficient knowledge of the physiological 

 chemistry of such small organisms as the insects, to enable us to determine 

 the exact nature of the subtle influences that decide whether an ant or bee 

 shall become a queen or a worker. 



The following observations relate to some of the unusual or pathological 

 individuals occasionally found in ant colonies, and referable, with more or 

 less probability, to trophic disturbances induced by specific parasites. The 

 inferences from these cases have a value approaching those derived from 

 experiment, since the phenomena make their appearance only under very 

 definite circumstances. 



PART I. OBSERVATIONS. 



1. The Parasitism of Orasema and other Chalcidid^ on ants. 



A. Orasema viridis Ashmead. 



This beautiful Chalcidid is abundant in Texas in the nests of Pheidole 

 kingi Andre subsp. instabilis Emery, but only from May to September. For 

 this reason I failed to notice it till May 25, 1903, about six weeks before I 

 moved from Austin to New York, although during my four years' residence 

 in Texas I had examined hundreds of instabilis nests during the autumn, 

 winter, and early spring months. I was so much impressed with the peculiar 

 behavior of the Orasema and the ants that I devoted to the subject every 

 available moment of the short remainder of my sojourn in Texas, but the 

 necessary preparations for my departure, the intense heat, which sets in 

 during the month of May, and a peculiar misunderstanding of the conditions 

 under which the Orasema develops, seriously interfered with the progress of 

 my work. It was only after I had left Texas that the study of preserved 

 material led me to what I believe to be a correct interpretation of the life 

 history of the insect. 



Before describing the Orasema and its development it will be necessary 

 to say something about the host. Ph. instabilis is a common ant in central 

 Texas and certain parts of Mexico, at least as far south as the State of 

 Morelos, where I have taken it near Cuernavaca. It forms populous colo- 

 nies which prefer to nest under stones in sunny places. In central Texas 



