Map 2, back behind the antelope and bison between AN and Army Fort.
How to kill them:
I did it as a hardmode pagan, full int. They were green to me. Basically rooted them and did quickest damage sequence.
These are for a hardmode quest btw, they don't give tremendous xp or special loots.
Attempt this solo in times of high blessing.
Bring a high level friend if you must. They do hit hard.
Look me up on Jedd/Jed if you need to do the quest.