Most San Francisco calls come in saying 'rats' even when it's actually mice — and a few come in saying 'mice' that turn out to be young roof rats. Here's how to tell the difference before you call.
Droppings tell you in 5 seconds
Rat droppings in San Francisco are typically 1/2 to 3/4 inch long, dark, and shaped like a fat grain of rice with blunt or pointed ends depending on the species. Mouse droppings are 1/8 to 1/4 inch — closer to a sesame seed.
If you're finding pellets in a pantry that look like cracked pepper, that's mice. If they look like a fat grain of brown rice, that's rats.
Sounds and timing
Mice scratch lightly and constantly — you'll hear them at all hours, often during the day. Rats are heavier, louder, and almost exclusively nocturnal. If the noise in the wall starts after about 10 p.m. and sounds like something running, that's rats. If it's a faint scratching that comes and goes around the clock, that's mice.
Entry point size
Mice get through a hole the size of a dime. Rats need something closer to a quarter. In San Francisco, the entry points we find on rat jobs are almost always around utility penetrations, vent screens that have rusted through, foundation cracks, and crawl-space access doors that no longer seat tight.
Why the answer changes the fix
Mice need finer-mesh exclusion and more aggressive interior trapping because they nest in smaller cavities. Rats need building-envelope work — hardware cloth and mortar at every penetration. Calling it the wrong species early means buying the wrong materials and missing the right entry points.
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