Rats are remarkably capable animals. They can squeeze through openings as small as half an inch, gnaw through concrete and copper, jump two feet straight up, swim for days, and carry diseases that spread to humans without direct contact. Whether you’re trying to keep rats out of your home or simply curious about their biology, here’s what these animals can actually do.
Squeeze Through Tiny Openings
An adult rat can fit through a horizontal gap of roughly 12 millimeters, about half an inch. For round holes, they need approximately 25 millimeters (one inch) in diameter. Young rats that have recently left the nest can manage even smaller openings.
Two physical traits make this possible. First, rats lack collarbones, so their skeletal frame is far more compressible than you’d expect for an animal their size. Second, their skulls are not fully fused. The bones can flex slightly under pressure, especially in younger animals, letting the rat essentially reshape its head to push through a tight space. If a rat can fit its skull through an opening, the rest of its body will follow.
Gnaw Through Almost Anything
Rat incisors score 5.5 on the Mohs hardness scale, which places them harder than iron, platinum, and copper. For reference, a diamond scores 10. This means rats can chew through wood, plastic, aluminum, cinder block, and even some types of concrete. They regularly gnaw through electrical wiring, which makes them a genuine fire hazard in homes and vehicles.
Their teeth never stop growing. The upper incisors grow about 2.2 millimeters per week, while the lower incisors grow around 2.8 millimeters per week. Rats need to gnaw constantly just to keep their teeth worn down to a functional length. If anything, gnawing isn’t optional for them. It’s a biological necessity.
Jump, Climb, and Swim
Roof rats can jump two feet straight up from a standing position and leap four feet horizontally. When jumping from an elevated surface, that horizontal distance doubles to about eight feet. Norway rats, the heavier species more common at ground level, are slightly less acrobatic but still capable climbers.
Both species are strong swimmers. Norway rats in particular can tread water for up to three days and hold their breath for several minutes, which is how they occasionally enter buildings through sewer lines and toilet pipes. Roof rats are better climbers, scaling brick walls, tree branches, and power lines with ease. Between jumping, climbing, and swimming, very few entry points are truly out of reach.
See in Near Darkness
Rat retinas are built for low light. Roughly 99% of their photoreceptors are rods, the type specialized for dim conditions, with cone cells making up only about 1% of the total. This gives them excellent night vision at the cost of sharp daytime detail.
Their color vision is unusual compared to ours. Rats have two types of cone cells: one sensitive to green light (peaking around 509 nanometers) and one sensitive to ultraviolet light (peaking around 358 nanometers). They have no significant response to light above 620 nanometers, which means they essentially cannot see red. This is why red lights are sometimes used in laboratories to observe rats without disturbing their behavior. They perceive a world shifted toward the ultraviolet end of the spectrum, detecting wavelengths completely invisible to humans.
Communicate With Ultrasonic Calls
Rats produce vocalizations well above the range of human hearing. When experiencing positive social interactions, such as play or physical contact, they emit rapid ultrasonic calls around 50 kHz. Researchers studying these calls found that rats being tickled produced as many as five distinct “trill” vocalizations in a single second. These calls are sometimes compared to laughter, though the comparison is imperfect. What’s clear is that rats use complex vocal signals to communicate emotional states to each other, and those signals are entirely inaudible to us without specialized equipment.
Spread Disease Without Being Touched
Rats carry a wide range of pathogens that can infect humans, and most transmission doesn’t require a bite. The major diseases linked to rats include leptospirosis, hantavirus, rat bite fever, tularemia, salmonellosis, and lymphocytic choriomeningitis virus.
Many of these infections spread through indirect contact. Rats with hantavirus, leptospirosis, and lymphocytic choriomeningitis virus typically show no signs of illness themselves, but they shed the pathogens in their urine. People get infected by inhaling contaminated dust, accidentally ingesting material from surfaces rats have contacted, or through broken skin that touches contaminated urine or droppings. Leptospirosis bacteria can even enter through small cuts or abrasions on your hands or feet.
Salmonellosis, campylobacterosis, and giardiasis spread through accidental ingestion of rat fecal material, often from contaminated food or surfaces in kitchens and pantries. Rat bite fever, as the name suggests, can spread through bites and scratches, but also through contact with rat saliva, urine, or feces, and even through contaminated food or water. Tularemia adds another route: it can become airborne if droppings or body fluids are disturbed and aerosolized, such as during cleanup of a rat-infested area.
What This Means for Rat-Proofing
Given these capabilities, effective exclusion requires attention to detail. Any gap wider than half an inch is a potential entry point. Materials like wood, plastic, and standard window screening won’t hold up against their teeth. Steel wool, hardware cloth with small gauge openings, and metal flashing are the standard barriers because rats can’t gnaw through them efficiently. Sealing gaps around pipes, vents, and utility lines is critical, since rats follow these features to find entry points.
Vertical access matters just as much as ground-level gaps. Tree branches within four feet of a roofline, unsecured vents, and gaps where utility lines enter the building are all viable routes for roof rats. Keeping vegetation trimmed back and screening any opening larger than a quarter inch for young rats helps cut off the most common paths inside.