Do you hate ants?
Them! is another one of those movies I caught on cable as a kid. While it is not exactly an eco-horror, it is a nuclear horror.
A nest of gigantic irradiated ants is found in the New Mexico desert; they quickly become a national threat when it is discovered that two young queen ants and their consorts have escaped to establish new nests. The national search that follows finally culminates in a battle in the concrete spillways and sewers of Los Angeles.
Anyway, the film is considered a classic and, unlike many other horror flicks from the 50s, isn’t considered “camp.”
Check it out.