Explanation of Names
Formica subsericea Say, 1836
Identification
"Recognizable by its slightly silky sheen (as the specific epithet suggests) and rounded rear margin of the head." --James C. Trager
Ellison et al. 2012 key Formica subsericea from F. glacialis and F. podzolica (for New England):
"The length of the antennal scape is longer than the length of the head"....subsericea
"...... shorter.............." other 2 spp.
This is not absolutely true:
Francoeur (1973) goes into great detail for the fusca group of Formica. The scape length of glacialis can exceed the head length (many specimens) and the scape length can equal the head length in subsericea (few specimens) (Fig. 269)
A similar situation for podzolica (Fig. 289).
However, there is no overlap between subsericea and the other 2 spp. when the scape length exceeds the head length by 0.1 mm.
In this NB specimen the scape length exceeds the head length by 0.18 mm which puts the ant way into subsericea territory:
Remarks
"By a considerable margin the most abundant and widely distributed black Formica east of the Rocky Mountains" -- James C. Trager
Internet References
Images at Mississippi Entomological Museum.