It’s an Aphaenogaster worker missing the metathorax and the propodeum. The mid-thorax is fused directly to the second abdominal segment, with the effect that the hind legs are just… gone. For comparison, have a look at a normal Aphaenogaster.
Myrmecologist Douglas Booher pulled her from a litter sample in Georgia. You’d think a major pair of walking legs would be indispensable, but this ant apparently was collected alive.