Originally posted by Honorable_D:

I've never seen 3 Seekers at once, they always seem to come as a pair and sometimes along with 3 Broods/3 Ticks.

not at night. but if you ever see 3 in ML biome, you are very, very likely to be near a mine. Game spawns seekers, furbys, skeletons, etc and then they run around killing each other. Usually the seekers win.