To the left in the photo taken by one of our technicians you can see a joist inset in a foundation wall, with a
sharp, brown grease line that goes under it. That is a classic rodent rub mark, from years of rodents running along the sill, encountering the joist, and running quickly down the wall, under the joist and back up. Rodents can easily run sideways on any porous surface, as illustrated by this rub mark. Rub marks are from sebum. Sebum is oil from sebaceous gland accumulated on rodents fur and left on surfaces passed. This material is the same as what causes “ring around the collar.” The more the rodents use a runway, the darker and more pronounced the rub marks appear.
Rub marks are useful in pest control because they identify runways and the sebum can be scrapped off and placed on traps or other rodent control devices. Adding sebum to a rodent control device will make it more likely to catch other rodents since it will have familiar smells on it.