What genus are thatching ants (I'm thinking Formica) cause I've never heard of that nickname and that's a massive anthill, the ground was probably to hard so they built into a loose soil mound. I might be wrong so if they dug into the ground as well then that's one big ant colony. Oh and that anthill could be really old cause some queens live up to 30 years old and some can have more than one queen so in theory the colony could last forever.