Crawlspaces are among rats’ favorite hideouts — here’s what to look for when tracking an infestation.
© slobo | iStock.com
Editor’s Note: This article was adapted from Techletter, a biweekly publication from Pinto & Associates, Mechanicsville, Md. To subscribe, visit www.techletter.com, or call 301/884-3020.

If you have an account with rats, whether indoors or out, don’t ignore the building’s crawlspace when looking for nest sites. Your inspection can’t be conducted the easy way, crouching at the crawl entrance and shining your flashlight back in the corners. To be effective, you must get down and dirty, willing to “crawl the crawl,” back to the darkest corners, looking for rats and their indicators.

SOIL BURROWS. If the crawl has a dirt floor, rats will often set up a burrow system even if other attractive nest sites are nearby. Check especially for burrows in mounds of backfill, a favorite burrowing site for rats.

DROPPINGS. A Norway rat produces 40 to 50 fecal pellets each day. Always an obvious sign, rat droppings usually will be concentrated in a few areas in the crawlspace, often away from nest sites. Inspection with a handheld UV light can help locate urine and droppings.

GNAWING. Rats will gnaw on many items including wood, aluminum, lead, plastic and mortar. Check floor joists and wall studs for tooth grooves and wood shavings beneath. Look for gnawing on any electrical wiring in the crawlspace.

SAGGING INSULATION. Rats often will nest behind ceiling or wall insulation. The rats’ movement often rips the insulation off of staples and nails, leaving it sagging and torn. Take a stick and tap the insulation and listen for the rattle of droppings, or even the scramble of disturbed rats.

RUB MARKS. The rats will enter other areas of the building through pipe runs, holes in cinder blocks or other access points. Look for dark, greasy rub marks around these holes. Rats leave rub marks on the wall next to established runways, and greasy swing marks around the bottom of joists when they travel along beams or sill plates. Look, too, for rub marks around vents and other openings leading outside.

DEAD RATS. Particularly if you have been baiting, look for dead rats on pipes, along the foundation walls, near burrow openings and in buckets, cans and similar containers.

ODOR. An experienced technician can smell a rat infestation in a crawlspace. It’s the combination odor of rat urine, droppings and dead rats. In the crawl, odor can often pinpoint areas in walls and ceilings where there is high rat activity.

The authors are well-known industry consultants and co-owners of Pinto & Associates.