What is the explanation to this lightning bug phenomenon?

I live on a farm and every night I go out by the woods and watch the stars. Sometime in early June last year, there were like 1,000,000 lightning bugs(NO JOKE) in this one corner of the wood. It was like a 4x4 sp[ot and like 20 feet tall. It was amazing but I cant seem to find an explanation! It wasnt anywhere else on the farm either??? Please cure my curiOSity!