A mouse can fit through a hole the size of a dime. Not a quarter. A dime. Once that fact lands, everything else about mice in Jersey City makes more sense.
Most of the housing in the Heights, Bergen-Lafayette, and Greenville went up before 1940. The brick is solid. The mortar holding it together? Less so. After eighty or ninety years of freeze, thaw, freeze again, those joints crack. The wood window frames shrink and pull away from the brick a little. The gap where the gas line enters the basement got sealed badly in 1955 and nobody has touched it since. Every one of those is a mouse door.
Then there’s the sewer system. Jersey City sits on top of a massive one, running under every block, and basically every restaurant on Newark Avenue is a 24-hour mouse food court. Mice that nest in the cracks under sidewalks travel up through utility chases into the apartments above the storefronts. You see this constantly in Journal Square and along Central Avenue. The restaurant doesn’t even need to be in your building. The mouse just needs the route.
Signs you’ve got mice (other than actually seeing one):
Droppings. Black, about the size of a grain of rice. Behind the stove, under the sink, the back corner of the pantry, along baseboards. Those are the usual spots.
A faint ammonia smell in cabinets that don’t get opened much.
Chewed corners on cereal boxes, dog food bags, anything with a paper edge.
Scratching in the wall at night. Mice are nocturnal, so you mostly hear them between 11 PM and maybe 4 AM. The first time you hear it, it’s surreal.
Greasy dark smudges along baseboards. Mice run the same routes night after night, and their fur leaves a kind of trail.
Getting mice out of an old Hudson County building is not about how many snap traps you set. You can catch ten mice in a week and still have a mouse problem, because more keep coming in through the same gap. The real work is exclusion. A decent mice exterminator in Jersey City is going to spend the first visit walking your basement, foundation, and utility entries with a flashlight, marking every gap, and sealing them. Steel wool, copper mesh, hydraulic cement. Mice can’t chew through any of that. Once the building is actually sealed, you trap out whatever is already inside over a few weeks. That’s it.
If you’re handy and you want to do a first pass yourself before calling anyone, the CDC has a step-by-step guide on sealing up your home against rodents. Common entry points, what materials work, what doesn’t. Worth reading.
A few quick wins for any Jersey City apartment:
Look at the gap under your front door. If you see daylight at the corners, a mouse fits through there. A door sweep solves it for ten bucks.
Check the dryer vent flapper. If it doesn’t shut all the way, that’s a mouse hole the size of your fist.
The hole behind the radiator where the pipe goes into the wall. Stuff steel wool in it, then caulk over the top.
Cats are useful, but only for mice that are already in the apartment. They don’t prevent entry. They just handle the consequences.
Last thing. If you keep finding droppings in the same exact spot week after week, even after trapping and sealing, you’ve probably got a nest inside a wall. That’s the point where DIY ends and somebody else’s flashlight starts.