These are pretty big ants (around 10mm long). The hole was in sandy soil and opened directly (i.e. without a mound). The nuptial flight was just about to start when I came across the hole, and it was interesting to watch how the workers seemed to be in charge of pushing/pulling out the winged ants (reproductive castes) then shoving them back into the hole again when danger threatened (i.e. the camera flashed).
Insecta: Hymenoptera: Formicidae
Carpenter ant = Camponotus japonicus = Kuro-oo-ari