We had them when we first moved into our house and then, we saw less and less of them as we trapped them, sealed up entry ways, properly stored food, etc. I don't really know what has changed but they are back with a vengeance. I have trapped and killed three in two days and I am certain that the traps will be full again tonight.
Mice seem to be especially persistent this year; perhaps they know something I don;t know about this coming winter.
Anyway, here is my advice on what to do if you find yourself with furry pantry thieves:
1. Check the outside and inside of your house for any visible cracks, opening, etc where the mice could be coming in and fill them in: Any place that a utility line enters or exits your house is a good place to start. Look behind/under your stove, your sink, your air conditioner, vents in a crawl space if you have one. Fill them in with silicon caulk or steel wool. Keep in mind that mice can squeeze themselves into REALLY small spaces.
2. Properly store your food (including pet food): Sometimes I get lazy about this, but in areas where you see evidence of mice, store food in plastic/metal/glass containers with tight fitting lids.
3. Clean up mouse droppings/urine properly: This means with a wet method. You should really never vacuum up mouse droppings or dried urine, you should always don gloves and maybe even a mask/respirator and use a cleaning solution with ammonia (if you don't mind using that in your house) or white vinegar (my preferred method) and a damp cloth. You can get seriously sick from mouse poop/pee. If you live in the Southwest US, the Hanta virus is a very real possibility, so do whatever you can to keep the poop/pee from becoming airborne and breathing it.
4. Trap, Trap, Trap!: I am not a fan of mice/rat poison for a number of reasons. 1. I have dogs, 2. I have a toddler. Either one could get at the poison. Even if I didn't have dogs or a toddler I would steer clear of poison because there is no telling where the mouse will die after eating it. It isn't instantaneous so they could crawl away and die in a wall or an inaccessible space and then you have rotting mouse carcasses to deal with... not fun. Not to mention, they could get out of your house and die where another animal could eat them, thus poisoning that animal, again... not good.
I like snap traps. Not the traditional kind you think of when you think "mouse trap" but the kind that look like a big clothespin.
These for example:
Bait the trap with peanut butter, set them, and catch your mice. These have the advantage of being reusable. They are easy to empty (with gloves on) and re-bait. They are quick killing and very effective.
There are new traps on the market that promise you won't have to see the mouse. They look like this:
I haven't had good luck with these traps, they always seem to be broken by the time I get them home from the store, plus, they are one use only which seems wasteful to me. (For another reason I don't like them, see #5)
I suppose glue traps are another option, but the mouse gets stuck on it and starves to death, slowly, which seems unnecessarily cruel to me.
5. Leave squeamishness at the door: You are killing a living thing. Deal with that. You are doing it as humanly as possible, take solace in that, but keep in mind that these critters have invaded your house, they spread disease (black death anyone?), and they need to be irradiated.
And please, do not catch and release... they are mice; there are plenty of them and they will find there way back in.