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Rodent Life Stages — Mice & Rats

Norway rats and house mice are the two primary rodent pests in Philadelphia. Both breed year-round indoors and can produce dozens of offspring per year from a single pair.

Birth

Newborn (Pinky)

Born blind, hairless, pink, 1.5-2g (mouse) or 5-6g (rat). Entirely dependent on mother. Nest is in insulated, dark areas: wall voids, under appliances, in insulation.

Week 2

Juvenile

Gray/brown fur appears by day 10. Eyes open at 12-14 days. Begins exploring outside nest at 3 weeks. Weaned at 21 days. Indistinguishable from adult by 4-6 weeks.

Adult

Adult House Mouse

12-20g, 6-9cm body. Large ears, pointed snout. Drops 50-75 fecal pellets per day. Sexually mature at 35 days. Up to 10 litters of 4-8 pups per year.

Rat

Adult Norway Rat

200-500g, 20-25cm body + 17-21cm tail. Blunt snout, small ears. Gnaws through wood, plastic, even soft metals. 4-6 litters per year, 6-12 pups each.

Signs

Droppings & Gnaw Marks

Mouse droppings: rice-sized, pointed ends. Rat droppings: capsule-shaped, 18-20mm. Gnaw marks on food packaging, wires, structural wood. Grease rub marks along walls.

Damage

Gnaw Damage & Nesting

Rodents strip insulation from wires (fire hazard), shred paper/fabric for nesting, and gnaw through PVC pipes. Structural damage accumulates rapidly with an established colony.

Images: Wikimedia Commons — free educational use

Mouse vs. Rat: How to Tell the Difference

Feature	House Mouse	Norway Rat	Roof Rat
Size	6-9cm body	18-25cm body	13-18cm body
Weight	12-30g	200-500g	100-300g
Color	Gray/brown	Brown/gray	Dark brown/black
Ears	Large relative to body	Small, thick	Large, thin
Tail	Longer than body	Shorter than body	Longer than body
Nose	Pointed	Blunt	Pointed
Droppings	3-6mm, rod-shaped	18-20mm, capsule	12mm, banana-shaped
Habitat	Inside homes, walls	Basements, ground	Attics, upper floors

Signs of Rodents in Your Philadelphia Home

💕 Droppings

Fresh droppings are dark and moist. Old droppings are gray and crumbly. Location indicates nesting area.

⚙ Gnaw Marks

Mice make small clean bite marks. Rats make larger, rougher marks. Gnawing on wires is a fire hazard.

👴 Runways

Dark grease marks and footprints along walls, baseboards, and behind appliances where rodents travel.

🏠 Nests

Shredded paper, fabric, insulation gathered in hidden areas like behind appliances and inside walls.

🎤 Sounds

Scratching, scurrying, or squeaking sounds in walls and ceilings, especially at night.

🐕 Odor

Musky, ammonia-like urine smell. Distinctive and strong in active infestations.

Philadelphia's Rodent Problem

Philadelphia consistently ranks among the top 10 most rat-infested cities in the United States. Norway rats are particularly common in South Philadelphia, West Philadelphia, and North Philadelphia. Roof rats are less common but found near the Delaware River waterfront. House mice are found throughout the city in virtually all types of residential buildings.

Rodent FAQ

How do rodents get into my home?

Mice can squeeze through a gap as small as 6mm (the size of a pencil). Rats need only 20mm. Common entry points include foundation cracks, gaps around pipes, dryer vents, utility lines, and doors that do not seal properly. Exclusion (sealing entry points) combined with extermination is the only lasting solution.

Are store-bought mouse traps enough?

Snap traps can be effective for minor mouse problems if you correctly identify and bait the runways. However, a true infestation requires professional treatment including colony baiting, exclusion, and follow-up inspections.

Are rodents dangerous?

Yes. Rodents carry Hantavirus, Leptospirosis, Salmonella, and other diseases. Rat bites can transmit rat-bite fever. Their gnawing on electrical wires causes an estimated 20-25% of all house fires of unknown cause.

Mice & Rat Identification in Philadelphia