How Long Have Rodent Pests Been Living Among Humans, And How Often Do Norway Rats Travel Into Homes Directly From Sewer Systems?

More than 2,000 rodent species have been documented worldwide, but only a very small minority of these species are known to be pests in human settings. The most ubiquitous rodents in the US include squirrels, voles, and prairie dogs, but house mice and Norway rats are the most abundant rodent species on earth. This is surprising to some considering that mice and rats are rarely spotted by humans. However, both house mice and Norway rats have learned to skillfully avoid human encounters in order to continue thriving on easily accessible resources in homes and buildings. In fact, the house mouse and the Norway rat both owe their success as species to their urban living conditions where abundant food, water and shelter allow the two pests to proliferate unchecked by predators and other evolutionary pressures associated with living in the wild. Once prehistoric humans abandoned nomadic hunting and gathering for a sedentary lifestyle, rats and mice immediately began exploiting human settlements for accessible resources. Considering that mice and rats first started to live among humans 15,000 years ago, it is not surprising that they are now adept at thriving in homes and buildings.

House mice (mus musculus) are easily the most commonly controlled rodent pests on both residential and commercial properties throughout the US. The most commonly controlled rodent species after house mice are Norway rats (Rattus norvegicus) and roof rats (Rattus rattus), respectively. Just as their common name suggests, roof rats are capable climbers that usually enter homes at elevated entry points, such as attic vents, gaps around cable and pipe penetrations, and even through vent pipes on roofs. Norway rats, on the other hand, are poor climbers that dwell in ground burrows, but due to their skilled swimming ability, Norway rats readily congregate in sewer systems where they take frequent dips. Naturally, Norway rats enter homes at ground level, but they have been known to burrow alongside foundations where they eventually locate a subterranean entry point into homes. Norway rats do not typically travel from sewers into homes through functional pipes, but they have been known to burrow upwards into the substructure of homes from sewer settings. Cases of rats being found in toilets and emerging from basement drains are increasing due to the deterioration of sewer infrastructure. More specifically, rats are exploiting breaks in terra cotta sewer pipes in order to travel into homes. Unsurprisingly Norway rats carry numerous disease pathogens and parasites, some of which include Leptospira interrogans, Bartonella elizabethae, and Rickettsia typhi.

Have you ever visually spotted or smelled a rat pest within or around your home that had clearly spent time in the sewer?