House mice frequently establish permanent shelter within concealed and often inaccessible indoor areas, most notably within wall voids, attic spaces, and crowded storage areas. It is often assumed that common Norway rat pests also frequently establish indoor harborages. However, while house mice often find indoor environments preferable to the outdoor environment, Norway rats naturally burrow into the ground in order to establish safe shelter from extreme weather conditions and predators.
Norway rat infestations commonly occur on residential properties where the pests establish one or multiple ground burrows throughout a yard. In some cases these ground burrows are excavated against the foundation walls of homes where rats are able to gain access into homes. In other cases, Norway rats establish above ground nesting sites within structures or within various manmade items, such as sheds, garages, furniture, vehicles, crawl spaces, foundation wall voids, overhead soffits, sign facades and beneath decks. Rats that nest within a home’s exterior nooks and crannies may forage primarily outdoors, or they may establish an interior infestation if easy access to an indoor food source can be secured more readily than outdoor food sources.
Newly established burrows may contain one single rat or an entire family of rats, which can consist of more than a dozen of the rodent pests. Well-established rat burrows consist of three 2 to 3 inch holes on the ground surface, one of which serves as the burrow entry point, while the other two holes serve as exit or “bolt holes” that allow the rat occupants to make a quick escape when burrows become flooded or invaded by their snake predators. Bolt holes are often located beneath bundles of lawn waste or beneath discarded materials found in yards, and the small size of both entry and bolt holes prevent predators from invading their burrows, with the exception of snakes, of course. Generally, burrows are between 12 to 18 inches deep, but burrows as deep as 4 feet are commonly found against foundation walls. This extra depth allows Norway rats to travel below foundations and into homes.
Have you ever encountered a rat burrow in your yard?