The short version
Rodent control in Maryland works when you seal the building first and trap second. House mice slip through a gap of 1/4 inch, which the CDC compares to the width of a pencil, so metal and sealant-backed steel wool along the sill plate do more than bait ever will. Norway rats need the same treatment at grade level.
- Sealing gaps is the durable fix; trapping alone empties a house that refills.
- A quarter inch of open gap is enough for a house mouse to enter.
- Norway rats and house mice are the two species reported across Maryland.
- Maryland's 26F median winter low pushes both species indoors in fall.
- Never sweep droppings; wet them down with a bleach solution first.
- Get a written quote after an inspection, with the entry points listed.
It is also for anyone who has already set a dozen snap traps, caught a few mice, and watched the noise come right back a week later. That pattern almost always means the building is still open somewhere. This is for homeowners who found droppings in a pantry, renters trying to get a landlord to act, and small-business owners who cannot afford a health inspection surprise.
What to look for
They ride wall cavities and pipe chases up from the basement into kitchens and attics, and they will nest inside an appliance if the space is warm. The local driver is the calendar. With a median winter low near 26F across the state's larger cities, outdoor food and cover fail in October and November and rodents move toward heated structures. A median summer high of 87F and 66 percent humidity keeps outdoor populations breeding hard all summer, so the fall push comes from a big base. Norway rats produce four to six litters a year, according to UC Statewide IPM, which is why a small problem in September is a loud one by January. Two species are on Maryland's list: the Norway rat and the house mouse. They want different parts of your building. Norway rats are burrowers. They work at grade and below, along foundation walls, under stoops and decks, into crawlspaces and basement floor drains, and they forage a hundred feet or more from where they sleep. House mice work vertically.
- 1Dark, rice-grain droppings along the back edge of a cabinet or on top of a basement joist.
- 2A greasy smudge line where fur has rubbed a pipe, sill or doorframe over and over.
- 3Scratching or rolling sounds overhead at night, usually starting an hour after the house goes quiet.
- 4Gnaw marks on plastic food packaging, cardboard boxes or the corner of a wooden door jamb.
- 5Soft golf-ball-sized nests of shredded insulation, paper or fabric behind stored boxes.
- 6Fresh soil at a rat burrow opening near a foundation, stoop or garden bed.
- 7A sour ammonia smell in a closed pantry, closet or crawlspace.
- 8The dog or cat fixed on one spot of baseboard for days.
Why it’s worth acting soon
- Populations compound quickly; a pair in October can be a colony by late winter.
- The CDC lists leptospirosis, rat-bite fever, salmonellosis, tularemia, hantavirus and LCM among illnesses spread directly by rodents.
- Chewed wire insulation inside walls and attics is a fire risk you cannot see.
- Urine and nesting ruin attic insulation, and replacing it can cost more than the trapping did.
- Droppings in a food-prep area can turn a routine health inspection into a shutdown.
Treatment options and typical costs
Exclusion and sealing
Quoted after inspection
A crew closes every opening a rodent can use, with hardware cloth, sheet metal, mortar and copper mesh rather than foam alone. This is the part of the job that lasts, because it changes the building instead of the population. On older masonry homes it includes utility penetrations, sill plate gaps, crawlspace vents and garage door sweeps.
- Time
- Depends on the opening list; sometimes staged over visits
- Best for
- Any structure with repeat activity or a history of mice returning
Snap trapping and monitoring
Quoted after inspection
Traps placed against runways and rub marks, checked and reset on a schedule, clear the animals already inside. Good technicians map catches by location, which tells you where the open door still is. Trapping is fast and visible, but on its own it is a recurring service rather than a fix.
- Time
- Until catches stop on scheduled checks
- Best for
- Active interior infestations, and any home where bait is off the table
Exterior rodent stations
Quoted after inspection
Locked, tamper-resistant stations along the building line reduce pressure from the outside, which matters where Norway rats burrow along foundations and travel between adjoining properties. Ask what is inside them, how often they are serviced, and what the plan is for finding and closing burrows rather than feeding them indefinitely.
- Time
- Ongoing while serviced on a set schedule
- Best for
- Rowhouses, restaurants and properties with rat burrows outdoors
Droppings cleanup and insulation replacement
Quoted after inspection
Contaminated insulation is removed, surfaces are disinfected and the space is restored. The CDC method is to ventilate 30 minutes, wet everything with a bleach solution of about 1.5 cups per gallon, let it soak five minutes, then wipe up, never sweeping or vacuuming dry material.
- Time
- Depends on how much insulation is affected
- Best for
- Attics and crawlspaces with heavy nesting or long-standing activity
Prices are typical published ranges. Ask what’s included before you compare quotes.
Crawl spaces are where rats and mice get comfortable. Vent screens, the sill plate and any gap around pipes are worth a careful look.Which rodents will you actually meet in Maryland?
House mice are the climbers. Knowing which one you have changes where the work happens. Maryland's species list names two: the house mouse and the Norway rat. The practical difference: mice are a sealing-and-trapping problem in the envelope, while rats are a yard, grade and burrow problem first. That range is why rat work has to cover a property line to property line, not just the kitchen where you saw the droppings. Because they forage well away from the nest, a rat living under a neighbor's deck can be eating from your compost every night. They dig along foundations, under concrete stoops, beneath sheds and into old sewer laterals, and they will use a basement floor drain or a rotted sill as a doorway. Norway rats are heavy-bodied burrowers that stay low. Find those and you have found the roadmap. A mouse needs almost nothing to get in, and it stays within a small home range once inside, so droppings cluster tightly along one or two runways. They exploit vertical routes, wall cavities, plumbing chases and the gaps around recessed lights, which is why the sound is so often over your head at night.
A month-by-month rodent calendar for a temperate state.
What you notice indoors during these months is usually rats in a crawlspace or garage rather than a full house infestation. Summer highs near 87F and humidity around 66 percent keep cover thick and food abundant, so numbers climb outside where you cannot see them. June through August is the outdoor population boom. This is the cheapest month range to do sealing, because populations are low and you are not trapping your way through a crowd. Outdoor food returns, breeding restarts, and any animals that wintered in your walls start moving between inside and outside. March through May is the quiet build. You can trap all winter, but sealing frozen exterior gaps is harder, and it often makes sense to trap now and schedule the exclusion work for early spring. Animals are already in and are moving inside walls for warmth, so scratching gets obvious. December through February is the loud season. This is when a house that still has open gaps picks up its winter population. As nights cool toward that median winter low of 26F, everything that spent the summer in a hedgerow or under a shed looks for a heated structure. September through November is the entry season.
This is what a proper seal looks like: metal mesh fastened with screws and sealed at the edges. Foam or caulk on its own gets chewed through.What should the first inspection actually cover?
Inside, they should be in the basement or crawlspace with a light checking the sill plate seam, the pipe chases and the joist bays, and in the attic looking for runways in the insulation, latrine areas and chewed wire. Expect the inspector to start outside and walk the entire perimeter, looking at grade level for burrow openings, rub marks and gnawed corners, then work up: utility penetrations, dryer vents, hose bib gaps, garage door corners, crawlspace vents, soffit returns, roofline junctions and the chimney. A real first visit takes time and produces a map, not a price. If a company quotes a number before doing any of that, you have no way to compare it against anyone else's number, because you do not know what is included. What you should get at the end is a list of specific openings with photographs, an opinion on which species and how established, and a scope that separates trapping from sealing from cleanup. Droppings tell them species and age; fresh ones are dark and soft, old ones are gray and crumble.
What moves the price of a rodent job?
Second is the count and difficulty of entry points: a handful of openings in accessible vinyl siding is quick, while the same number in old brick means mortar work and a mason's patience. Mice in a single pantry cabinet is a different job from activity in the kitchen, attic and crawlspace, because each area needs its own trapping and its own inspection time. Spread comes first. Here is what the estimator is actually pricing. Nobody can give you an honest figure sight unseen, and the range between two homes on the same street can be wide. A cheaper seal with no coverage is not the better deal it looks like. Finally, ask what the exclusion warranty covers, how long it runs and what voids it. Follow-up visits matter too: quotes vary widely in how many trap checks they include. Removing contaminated attic insulation, disinfecting and re-insulating can exceed the cost of the pest work itself, so ask whether it is in the quote or excluded. Cleanup is the line item that surprises people.
Rowhouses, party walls and why one unit is never the whole job.
That means two things for anyone in a rowhouse or a converted multi-unit. You can seal your own exterior perfectly and still hear activity, because the animals are entering from next door through a floor joist pocket or an old chase. When buildings share a party wall, a shared cellar or a common roof deck, mice travel the length of a block inside the structure without ever going outdoors. Attached housing changes the math, and if your Maryland home shares a wall, it applies to you. Ask a provider whether they already service adjoining addresses, and whether they will document the shared-wall openings in writing so a landlord or an association has something concrete to act on. If neighbors treat at the same time, the population has nowhere to shift; if they do not, you are running a permanent trapping program on animals that live elsewhere. Second, coordination pays. First, interior sealing matters as much as exterior sealing: the holes around a shared soil stack, the gap where a joist enters the party wall and the space behind a kitchen cabinet base all need closing with metal, not foam.
How to compare two rodent quotes without guessing.
Check five things. The cheap one is often cheap because it is only trapping. Put the two proposals side by side and read for scope rather than price. Get everything in writing after the inspection, and be skeptical of any pressure to sign on the spot, since a rodent problem that has been building since fall can wait a couple of days for a second opinion. The answer separates a company that stands behind its sealing from one selling a monthly route. A useful question for either company: if we do this work and I hear activity again in eight weeks, what happens? And what does the exclusion warranty actually promise, for how long, and what voids it? Is droppings cleanup or insulation replacement in the number, or a separate proposal? How many service visits are included, and what happens after those run out? What materials will close them, since hardware cloth, sheet metal and mortar hold up where expanding foam alone gets chewed through? Does the quote list the specific entry points found, or does it say sealing in general terms?
What affects the price
- How far the infestation has spread: one kitchen versus kitchen, attic and crawlspace.
- Number of entry points that need sealing, and whether they are reachable or buried behind finished walls.
- Construction type, since brick and stone penetrations take mortar work that vinyl siding does not.
- Whether attic insulation removal and droppings cleanup are part of the scope or a separate line.
- How many follow-up visits are included before the account moves to maintenance.
- Exclusion warranty terms, including what voids them and how long the sealing is covered.
- Access conditions such as a low crawlspace, a finished basement ceiling or a steep roofline.
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What is your biggest concern about rodents in your home?
When to call for help
Ask any company you talk with to show you the openings they found, in photographs, before quoting the sealing work. Also call if you rent or manage property, because documenting entry points in writing is what moves a repair from a maybe to a scheduled job. Those situations need a person who will get on a ladder, into the crawl, and along the whole foundation line with a mirror and a flashlight. Call someone when you hear activity in more than one part of the house, when you find rat burrows outside, or when droppings show up in an attic or crawlspace you cannot safely work in.
What you can do yourself
Cleaning up food sources, moving bird seed and dog food into metal cans, cutting back ivy against the foundation, putting a sweep on the garage door and stuffing copper mesh into a pipe gap under the sink are all reasonable Saturday jobs, and they matter. Do it yourself where the work is visible and low. Sealing most of them still leaves a working door. The other reason to hire is diagnosis: a homeowner often finds a few entry points and stops while the building has more. Roof-line sealing, soffit and ridge gaps, crawlspace work around ductwork, burrow tracking across a property line and any contaminated insulation removal are worth paying for. Hire out the parts that need height, confined space or judgment. Well-placed snap traps along a basement wall will catch mice.
Where you live matters
A detached home is more likely to leak at utility penetrations, garage doors and crawlspace vents. Attached houses let mice travel wall to wall, so a neighbor's problem becomes yours through a shared cavity, and treating one unit rarely settles the block. Across the cities in our data, from Baltimore and Silver Spring to Columbia, Germantown and Frederick, the first rodent question in Maryland is whether your home is attached or detached, because the two fail in different ways. The weather adds pressure: summer highs near 87F build the outdoor population, winter lows near 26F push it indoors, and about 42 inches of rain a year keeps soil workable for rats burrowing along foundations and under stoops. Median home values around $395,000 mean most owners are protecting a real asset, and attic insulation ruined by nesting is one of the more expensive avoidable outcomes.
Simple ways to keep rodents away
- Walk the foundation twice a year and fill anything a pencil fits into with copper mesh and sealant.
- Screen crawlspace vents, dryer vents and weep holes with quarter-inch hardware cloth rather than plastic louvers.
- Put a new rubber sweep on the garage door; the corners rot out first and rats use them.
- Store pet food, birdseed and bulk grain in metal or thick rigid plastic, not paper sacks.
- Trim shrubs and ivy back six to twelve inches from siding so runways are exposed.
- Keep firewood off the ground and away from the house through the wet months.
- Fix the drip under the hose bib; with 42 inches of rain a year the ground stays soft, but a steady interior leak is what keeps rodents in a wall.
- Cap chimneys and cover attic gable vents with metal mesh.
- Empty outdoor trash into cans with tight lids and rinse the cans after fall cookouts.
Before you call, sketch where you have seen droppings or heard noise and measure any gaps you found. It makes the first visit faster and the quotes comparable.Did you know?
A single Norway rat pair can wean twenty or more offspring in a year across four to six litters, while roof rats run three to five litters of up to eight.
The CDC counts leptospirosis, rat-bite fever, salmonellosis, tularemia, hantavirus and LCM among the illnesses rodents spread directly to people.
Human plague still occurs in the United States at an average of about seven cases a year, concentrated in northern New Mexico, northern Arizona, southern Colorado and parts of California, southern Oregon and far western Nevada.
Questions people ask
What kinds of rodents get into homes in Maryland?
Mice are the ones you hear in the ceiling and find in a pantry, since they climb wall cavities easily. Norway rats stay lower, burrowing along foundations and getting in at grade, and they range a hundred feet or more from the nest while foraging. House mice and Norway rats are the two species listed in Maryland's rodent data.
How small a hole can a mouse use?
That is why sealing has to be done with a flashlight and a careful hand rather than by eye from ten feet away. Rats start with the same size opening and chew it wider, so a gap you dismissed in spring can be a rat run by fall. A quarter inch, which the CDC describes as about the width of a pencil.
Is trapping enough on its own?
Houses that get trapping only tend to go quiet for a few weeks and then start up again, especially in October and November when outdoor cover fails. Sealing is what makes the quiet permanent. No. Trapping removes the animals in the building right now, which is worth doing, but it does nothing about the opening they used.
Should I worry about hantavirus here?
Of the 890 hantavirus cases the CDC has recorded since 1993, 94 percent occurred west of the Mississippi, and the carrier is the deer mouse in sheds, cabins and garages rather than the house mouse in a kitchen. Handle droppings carefully anywhere, but the western risk profile does not transfer. It is a small risk in this part of the country.
What about leptospirosis in Maryland?
Nationally the count was 21 versus 22 over that window. Those are small numbers, but they are the reason to keep rat burrows out of yards where dogs and kids spend time. Rats are a known urban reservoir for it, and the CDC's weekly disease tables recorded 2 Maryland cases through week 13 of 2026 against 1 in the same stretch of 2025.
How do I clean droppings safely?
Mix roughly 1.5 cups of bleach per gallon of water, which is a one-to-nine solution, spray the droppings and nesting until wet, and let that sit five minutes before wiping it up with paper towels. Never sweep or vacuum dry material, because that puts particles into the air. Open the space and let it air out for 30 minutes before you go in.
How fast does a small problem get big?
UC Statewide IPM reports that Norway rats have four to six litters a year and wean twenty or more offspring annually, and house mice breed at a similar clip. A pair that moves in behind a Maryland garage wall during the first cold snap can be a group with established runways and multiple nests by the end of winter. Faster than most people expect.
Who pays for sealing in a rental?
The practical move is documentation: photograph droppings and gaps, put the request in writing with dates, and ask that the inspection report list entry points. Food storage and trash handling sit on the tenant's side. Sealing a sill plate or replacing a garage sweep is building maintenance rather than housekeeping, so it belongs in a written request to whoever maintains the structure, and the lease will say how repairs are assigned.
What should a written quote include?
Get all of that after a walkthrough rather than over the phone. A quote given without someone looking at the crawlspace is a guess. Ask for the entry points found and how each will be sealed, the materials being used, how many trapping visits are included, whether cleanup and insulation are in scope or extra, and the exact terms of any exclusion warranty.
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The facts in this article come from the public sources listed above. Every home is different, so ask the company you talk to about pricing and what’s included. Published by Rodent Exterminator · Updated October 11, 2026 · How we write these guides