OBSERVATIONS ON ARMY ANTS IN BRITISH GUIANA.i 



By William Morton Wheeler. 



Received February 16, 1921. Presented February 9, 1921. 



Although the progress of myrmecology during the past twenty 

 years has been so rapid that more seems to have been written on the 

 subject during that period than throughout the nineteenth century, 

 there are several problems that yield to solution very slowly and 

 reluctantly. One of these is the ethology of the nomadic legionary, 

 or army ants of the subfamily Dorylinee, which possess worker, male 

 and female forms so peculiarly specialized and diverse that they can 

 be correlated with certainty only when captured in the same colony. 

 The workers are rarely encountered, except when foraging and at 

 seasons of the year when the brood is not well developed, the males 

 are seldom seen, except at lights, and the huge wingless females are 

 among the rarest of insects. Notwithstanding all these obstacles, 

 considerable information has been gradually accumulated concerning 

 the Ethiopian and Indian species of the genera Doryhis and Mnictus 

 by Emer}^ Forel, Santschi, Brauns, Vosseler and others. Less 

 progress has been made in the study of our American species, which 

 belong to the genera Eciton and Cheliomyrmex. 



Emery divides the former genus, which comprises more than a 

 hundred described species, and ranges from Argentina to North 

 Carolina, Missomi and Colorado, into three subgenera: Eciton sens, 

 str., Lahidus and Acamatns. The genus Cheliomyrmex contains only a 

 few rare species, and ranges only from Brazil and British Guiana to 

 tropical Mexico. While the females of certain species of Lahidus and 

 Acamatus are known, those of Eciton s. str., have been sought in vain 

 for over half a century. During the summer of 1920, while I was 

 working at the Tropical Laboratory of the New York Zoological 

 Society at Ivartabo, British Guiana, I was able to secure the female of 

 E. hurchelli, its males and those of E. (A.) pilosum Smith, and to make 

 observations on the habits of these and several other species. As my 

 first myrmecological paper, on some Texan Ecitons, was published 

 just twenty years ago, and as I have not since had occasion to con- 



1 Contributions from the Entomological Laboratory of the Bussey Institu- 

 tion, Harvard University, No. 183. 



