Explanation of Names
Neivamyrmex opacithorax (Emery, 1894)
The worker is almost has a shiny red head and gaster and weakly-shinging to matte, slightly darker mesosoma; the rear margin of the head is scooped out, with angular but rounded corners.
Det. Steven Wang, 2018
se US to Calif. - Map (1)
The second most widely and northerly distributed army ant (following the related N. nigrescens), extending to the Carolinas, then around the bottom of the Appalachian Range and north again to southern Illinois and west to the Missouri River up to southwestern Iowa, then westward to Colorado, generally avoiding the mountains (but see record from Flagstaff AZ), all the way to the West Coast.
Under large rocks in sunny places in spring, more secluded subterranean cavities during hot weather, such as abandoned burrows or ant mounds taken over during a raid.
Spring warm-up till first frost.
Often observed with harvested brood of other ants, but also reproted to eat carabid beetles. "Neivamyrmex opacithorax appears to feed almost exclusively on ants and carabid beetles. The capturing of larval and adult Carabidae seems to be a common occurrence since three colonies of opacithorax in Kansas had killed numerous specimens, and Wheeler and Long (1901: 163, digital link below),reported that opacithorax in Texas had captured "a considerable number of small carabid beetles.”
Colonies often gather under large rocks in sunny places in spring, commencing the first of their monthly brood cycles for the season; the last brood, containing the huge winged males and a few virgin queens, is reared in September.
These are rather typical column-raiding army ants, much like the more conspicuous ones known from the Tropics, save for the fact that they shut down brood production in winter.