SYSTEMATIC POSITION. 31 



vidual we have ever seen measuring 2.75 mm. If workers are more 

 than 3 mm. or less than 2 mm. in length, it may be safely concluded 

 that the ant under observation is of some other species. The Argen- 

 tine queen, however, is from 4.5 to 5 mm. in length. The color of 

 the Argentine ants — all adult forms — is a very deep brown, ahnost 

 approaching black, and the color is uniform over the entire body. 

 The possession of head and thorax of one color with abdomen of a 

 different color immediately eliminates a specimen from this species. 

 A colony containing workers of more than one size is also eUminated, 

 since all Argentine workers are of one size or caste. The fact that the 

 petiole or pedicel (connecting joint between the thorax and abdomen) 

 of /. Tiumilis consists of only one segment readily distinguishes it from 

 the species of Solenopsis and other myrmicine ants. The pupae of 

 our species is never inclosed in cocoons, but always naked, with legs, 

 eyes, segments, etc., plainly visible. Argentine workers, when 

 crushed between the fingers, give no perceptible odor, and this readily 

 distinguishes them from their closest relative, 7. analis, as well as 

 from their more remote relatives, the species of Tapinoma. The 

 Argentine worker does not possess a functional sting and does not 

 even attempt to sting. This again separates the workers from those 

 of a great many species, including Solenopsis, most of which sting 

 viciously upon the slightest provocation. Upon being disturbed, 

 particularly in the nest, some of the Argentine workers will attempt 

 to bite, but by far the great majority devote their energies to escaping 

 rapidly or to removing the larvae and pupae to a place of safety. 

 Wliat few do attempt to bite are not successful in piercing the skin 

 of one's hands owing to their weak jaws. It is only when reaching 

 tender places, such as the skin between the bases of the fingers for 

 example, that they are able to make their l:)ites effective. 



If, therefore, ants suspected of being Indomyrm,ex humilis meet the 

 following quaUfications, and in addition exhibit the habits already 

 described, there is a reasonable probability that they belong to this 

 species, and examples should be submitted to a specialist for exam- 

 ination : 



Workers not over 3 mm. nor less than 2 mm. in length 



Workers uniformly colored; deep brown, nearly black. 



Workers of uniform size; no distinction as to caste. 



Workers traveling in well-defined trails or lines to and from the nest. 



Workers emitting no offensive odor when crushed. 



Workers unable to sting and unable to bite effectively. 



Pupfp not inclosed in cocoons. 



Petiole or pedicel consisting of only one segment. 



Petiole prolonged dorsally into a wedge-shaped scale, inclined slightly forward. 



Epinotum devoid of a pointed or conical elevation. 



Ocelli absent in workers, present in queens and males. 



