From what I know, the answer to that is simple;
Did you have a Pest Inspection?
Remembering that I am not a lawyer, nor do I pretend to be:
We give our Clients a document to sign, when we begin an offer; It urges clients to get inspections.
My guess is that you have bought an ant hill.
But do not take my word for it.
The chickens are all out now, but I would suggest a Pest Inspection now, so that you know the extent of your problem.
THEN, go see a lawyer.
Good luck and may God bless