Raccoons (Procyon lotor) are adaptable, intelligent mammals that flourish in urban landscapes. These creatures have successfully integrated into human environments, exploiting the abundance of food and shelter found in cities and suburbs. Their resourcefulness often leads to questions about whether they establish permanent homes within underground infrastructure like sewer systems.
The Truth About Raccoons and Sewer Systems
Raccoons generally do not establish permanent residency or raise their young inside municipal sewer systems. The environment within a functioning sewer is frequently wet, subject to strong, unpredictable flows, and contains potentially toxic gases such as hydrogen sulfide, making it an unsuitable den site. Instead of serving as a home, underground pipes are utilized as temporary travel corridors or foraging spots.
They primarily seek secure, dry, and temperature-controlled den sites for sleeping during the day and for raising their kits, which are born in the early spring. Preferred urban dens include attics, uncapped chimneys, sheds, under porches, and hollow logs, all of which offer warmth, safety, and protection from predators. Their presence underground is typically transient, driven by immediate needs.
Why Raccoons Enter Underground Infrastructure
Raccoons enter underground infrastructure, particularly storm drains and sewer access points, for several opportunistic reasons. These systems provide a sheltered route for nocturnal movement, allowing them to avoid high human traffic and other predators. The pipes also offer a stable thermal environment, being cooler during summer heat waves and warmer when winter temperatures drop.
The primary motivation for entering these spaces is often foraging, as raccoons are omnivorous scavengers. Food scraps, grease, and other organic matter wash into the drains, creating a concentrated food source. The underground environment also offers easy access to standing water, which is important for both drinking and for their characteristic behavior of manipulating food.
Health Risks Associated with Raccoon Presence
The presence of raccoons near and within human infrastructure introduces specific public health risks, mainly through the contamination of surfaces and soil with their feces. A significant concern is the Raccoon Roundworm (Baylisascaris procyonis), a parasite that is widespread in raccoon populations, with infection rates up to 90% in juveniles. The roundworm eggs are shed in feces, often deposited in communal outdoor defecation areas called latrines, which can include flat surfaces like decks, rooftops, and tree bases.
If these microscopic eggs are accidentally ingested by humans, the larvae can migrate through the body, causing a severe and potentially fatal condition known as neural larva migrans. This involves damage to the brain and central nervous system. The eggs are highly resilient and can remain viable in the environment for years, posing a long-term hazard. Raccoons also carry the bacteria that causes leptospirosis, which is shed in their urine and can contaminate water sources, leading to kidney or liver damage in humans and pets.
Exclusion and Prevention Strategies
Minimizing raccoon access to properties is the most effective way to reduce the risk of them using nearby drains or sewer openings. Securing all outdoor food sources is primary, requiring the use of heavy-duty garbage cans with tightly secured, raccoon-proof lids or storing cans inside a garage or shed. Pet food and bird seed should be removed from outdoor areas every night, as these are strong attractants.
Exclusion efforts should focus on sealing potential den sites around the home. This involves inspecting and sealing all exterior openings, such as gaps in the roofline, vents, and crawl spaces, using durable materials like heavy-gauge wire mesh. For infrastructure prevention, ensuring that storm drain grates are securely fitted and undamaged eliminates easy entry points into the underground system. Regular inspection for signs of raccoon activity, particularly latrines, allows for prompt and careful removal of contaminated materials.