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 
J 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, almost 
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 eliminated, 
since all Argentine workers are of one size or caste. The fact that the 
** petiole or pedicel (connecting joint between the thorax and abdomen) 
|jj of /. Jiumilis 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, 
'v x 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, /. 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 
yL rapidly or to removing the larvae and pupae to a place of safety. 
What 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 
j tender places, such as the skin between the bases of the fingers for 
example, that they are able to make their bites effective. 
1^ If, therefore, ants suspected of being Iridomyrmex Jiumilis meet the 
^ following qualifications, and in addition exhibit the habits already 
described, there is a reasonable probability that they belong to this 
|y species, and examples should be submitted to a specialist for exam- 
ination: 
Workers not over 3 mm. nor less than 2 mm. in length 
-i > Workers uniformly colored; deep brown, nearly black. 
Workers of uniform size; no distinction as to caste. 
J Workers traveling in well-defined trails or lines to and from the nest. 
Jj L Workers emitting no offensive odor when crushed. 
1 Workers unable to sting and unable to bite effectively. 
| t Pup^p not inclosed in cocoons. 
Petiole or pedicel consisting of only one segment. 
Mi 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. 
