Yeah most likely your chimney. Just the other day I went to light a fire, opened the flue and about 20 of the buggers fell out right onto my hand. Scared the crap out of me, but luckily because it was cold they weren't moving much so I didn't get any bites/stings. I grabbed 2 aim n flamer lighters set the fake log on fire, closed the mesh screen and stood on guard for the next 30 mins 1 in each hand.