Haidomyrmecinae

Haidomyrmecinae, occasionally called hell ants, are an extinct subfamily of ants (Formicidae) known from Cretaceous fossils primarily found in amber from North America, South America, Europe, and Asia, spanning the late Aptian to Campanian, around 113 to 79 million years ago. The subfamily was first proposed in 2003 but had been subsequently treated as the tribe Haidomyrmecini and placed in the extinct ant subfamily Sphecomyrminae. Reevaluation of the Haidomyrmecini in 2020 led to the elevation of the group back to the subfamily. The family contains nine genera and 13 species.

Members of this family are highly distinct from all other ants, having diverse head ornamentation, and unusually shaped, extended mandibles that are articulated vertically rather than horizontally as in modern ants. The jaws in combination with the head ornamentation served to restrain prey, with most species having setae (hair-like structures) covering parts of the head, which likely functioned as triggers to rapidly close the jaw when disturbed, similar to those of modern trap-jaw ants. Fossils indicate that haidomyrmecines were able to take prey solitarily. Like modern ants, they were eusocial, with distinct worker and queen castes, likely with relatively small colony sizes. Due to their lack of metabolic stores, the queens likely engaged in hunting during the initial foundation of the nest. Haidomyrmecines are thought to be amongst the most basal and earliest diverging group of ants known.