THE FEMALE OF FORMICA OPACIVENTRIS EMERY 
(FORMICIDAE) 
By Robert E. Gregg 
Department of Biology, University of Colorado 
The forms of Formica exsecta constitute a small, well 
defined group of ants easily recognized by the excavated, 
or broadly emarginate, occipital border of the head. Only 
three of the North American variants are now considered 
valid ^Creighton, 1950, for synonymy). All the castes of 
Formica exsectoides and F. ulkei have been described pre- 
viously, but the worker and male alone were the castes 
hitherto known for F. opaciventris, the female having 
escaped collection. I am now able, however, to fill this gap 
by presentation of the description of the opaciventris queen. 
Dr. Creighton cites the mountains of Colorado and 
Wyoming as the range of this species, and states that it 
appears to be confined to high intermountain valleys, and 
does not occur on the eastern slope of the Rockies. The 
nests he observed were built in hard, stony soil, and 
consequently differed much from the nests of the eastern 
exsectoides and ulkei which are usually in moist, spongy 
earth. 
Near the village of Valmont, Colorado, five miles east 
of Boulder, is an assemblage of mound nests of Formica 
readily visible from the road. The nests are in a low, 
moist meadow at approximately 5160 feet, and partly 
arranged with reference to the water table in that most of 
them are present on slightly higher ground and fewer are 
in the swales where alkali accumulates from the evapora- 
tion of water. 
These mounds are occupied largely by Formica altipetens , 
but some are constructed by opaciventris. With Dr. 
Creighton, I visited the area on November 29, 1950, and 
by careful excavation of one of the nests, we discovered 
the single deflated female of Formica opaciventris. This 
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