1903.] NATURAL SCIENCES OF PHILADELPHIA. 215 



A REVISION OF THE NORTH AMERICAN ANTS OF THE GENUS 

 LEPTOTHORAX Mayr.' 



BY WILLIAM MORTON WHEELER. 



The diminutive species of the cosniopohtan genus Leptothorax are 

 among the most interesting though least conspicuous of our ants. 

 No other group of Formicidse appears to present such diversity of 

 habits, while at the same time adhering so closely to certain rather 

 definite generic peculiarities. The species all form small colonies, 

 often of not more than twenty-five to fifty individuals, and occupy 

 small cavities in the soil, or between stones, or in the tissues of plants. 

 These cavities are either of their own excavation, or found ready to 

 their use in the form of accidental openings or the burrows and gal- 

 leries of larvas, other ants, etc. Favorite nesting-places are the 

 abandoned woody galls of the Cynipidae, like the galls of Holcaspis 

 cinerosus on the live-oaks of central Texas, the galls of Diptera, like 

 Trypeta soUdaginis on the golden-rod, etc. Even hollow nuts on 

 the ground under the trees are sometimes tenanted by species of 

 Leptothorax. Brief notes on the nesting habits, so far as these are 

 known, are appended to the descriptions of the different species enum- 

 erated below. 



The small size and obscure location of the Leptothorax nests, which 

 form a remarkable contrast with the teeming, conspicuous formicaries 

 of other ants like Formica rufa, F. exsectoidcs, Pogonomyrmex barbatus 

 and Ischnomyrmex CockereUi, will readily account for our rather 

 limited knowledge of the North American species. Then, too, none 

 of our Leptothorax are really common, except in certain circumscribed 

 localities, so that the discoA-ery of the species is more often a matter of 

 accident than of deliberate search, even when one is out looking for 

 ants and nothing else. Single workers are found running about on 

 the ground or on the trunks and branches of trees in search of sweet 

 exudations, small insects or the remains of large insects that have 

 been rejected by si^iders, birds, etc. The nests are most readily found 

 by following up such single workers, often a tedious and time-con- 

 suming task, as these insects will sometimes run about for an hour or 



1 Contributions from the Zoological Laboratory of the University of Texas, 



No. 48. 



