Mice came out of the holes and the exterminator plugged the holes up with steel wool. Mice come and go from the same path. They can't get back into their exit point so they will run around until they are caught. I would place glue traps in the area until they are all caught.

The solution is so simple, it's been used for millennia: See if he'd consider getting a cat. That is the one surefire thing that works.

BN: Your SH may be clean, but if he has a hole in a wall mice can get in the apt if they find it. Your exterminator overlooked it when he put in new heaters or didn't look everywhere. Check where sink pipes go in the wall, behind the range/fridge/dishwasher and around electrical outlet wall plates.

Mice can chew or push thru steel wool. Stuff holes with fine copper wire mesh then seal it with silicone. Mice won't chew copper; it's poisonous to them. If there are exhaust vents on kitchen/bath walls, put a sheet of copper wire mesh behind the cover panel.

Also, if the SH below has dogs/cats, mice in the walls (and all bldgs have mice in the walls) may smell pet food, esp if it's not eaten and left out too long. If they can't get into that apt, they'll go in any nearby hole they find. Mice will climb UP inside walls to floors above but they seldom climb down to floors below.

Thanks all BT participants for sharing suggestions with me. We've had exterminator in since I posted and they sprayed foam into all the crevices and spaces recommended. It's pretty unsightly, but SH seems to have some relief from mice for a couple days. I will discuss copper mesh/silicone as next step. We're considering having exterminator come and do an inspection of outside of building for entry points. It's not very $$- $100, they will then make suggestions for mouseproofing perimeter. Think this is a good step?

BN: Spraying foam in holes helps for a while but it turns to liquid and will eventually evaporate. Holes have to be sealed.

We did major extermination a few years ago. The result was great. We sealed holes on the bldg exterior on the ground floor. Once mice get into the bldg, they can go thru walls and get into any hole they find -- in apts and in bldg service areas.

We were painting all our bldg service areas anyway so when we removed all the equipment and supplies from the offices, trash areas, store rooms, etc., our exterminator sealed holes before we painted and put everything back in place. We also sealed holes in the compactor, boiler, oil tank and meter rooms. We were amazed at how many holes and wall fissures were found in those areas. We put metal sweeps on all service room doors (not rubber, mice can chew thru it) and got new trash bins with attached covers.

We sent residents a firm memo reminding them to discard trash properly and to seal holes in their apts. and we kept on top of this. We've had no complaints of mice/bugs since.

Interestingly, we also found that after we sealed all the holes in bldg service areas, the temperature on the ground floor was 8-10 degrees higher, so we've saved money on the cost of heating the lobby and the hallways to ground floor apts.

BN - You may not want to go as far as we did but I recommend your exterminator checking the bldg exterior for entry points and doing any common are interior work you can afford. People still have to seal holes to keep mice out of their apts, but anything you can do to keep mice out of the bldg, and inside the walls if they do get in, is worth the effort.

Thanks for info. I asked exterminator if he handles sealing up perimeter holes on the outside and inside, such as in our basement which has old brick walls. He doesn't do certain types of hole sealing that involve more than--? Is there someone you can recommend who can fill holes in walls with whatever needs to be used. Maybe we need a different exterminator? He said he used to recommend people to seal masonry but then it backfired if they didn't do a good job.

BN: Many exterminators won't seal holes, or charge a lot for it. Ours located and marked holes with chalk. Since we were painting our bldg service areas anyway the painters we've used for years patched the holes before they painted. A few wall fissures in the boiler room, compactor room, etc. were so wide they couldn't be patched. They had to be filled with poured concrete. A lot of bldgs don't think about maintenance in rooms like these. There can be holes/cracks in them for years. If holes from outside give mice entry points into the bldg, they can then travel around in the walls and find their way to apts.

If you don't seal exterior masonry, at least seal what you can inside the bldg.