If you have a lot of lights on they're probably attracted to the light...the flying ones, anyway. Don't know anything about silverfish. Have you checked to see that all the windows/screens are closed and that there are no holes in the screens? Also, maybe check around the sill to see if there's a gap that's letting them in? I had a little gap when I stayed in WI last summer and it let a ton of bugs in before I just taped up the edges of my window with packing tape so the bugs couldn't get in anymore. Good luck!