There is actually three 1" holes about 1" apart just above the landing board, they are only doing this overnight and I assume its because they are crowded at night, they have plenty of room inside, they just are not using it yet. One of my langs started doing this last night, despite having plenty of room, however by this morning they had all withdrawn into the hive. The TBH supprised me a little as with the bottom open they actually have more "air" than the langs, but then the TBH has acted completely independant when compared to the other hives.