Why do rats live in sewers? - briefly
Rats occupy underground drainage networks because they provide plentiful food waste, protection from predators, and consistent moisture and temperature conditions.
Why do rats live in sewers? - in detail
Rats occupy underground drainage networks because these environments satisfy several physiological and ecological requirements. The tunnels provide constant darkness, which reduces exposure to aerial predators such as hawks and owls. The temperature inside the pipes remains near 20 °C year‑round, eliminating the need for seasonal thermoregulation and allowing continuous activity. Moisture levels are high, preventing dehydration in a species that loses water rapidly through respiration.
Food sources are abundant. Human waste, spilled food, and organic debris accumulate in sewers, creating a reliable supply of calories. Decomposing matter releases nutrients that support both the rats and the microbial communities they feed on. In many cities, the flow of wastewater carries organic particles directly to the rats’ foraging grounds, reducing the distance they must travel to locate sustenance.
Structural features of the system aid movement and shelter. Pipes are smooth, allowing rapid locomotion and escape from threats. Junctions and manholes act as entry points, while the labyrinthine layout offers numerous nesting niches. Cracks, joints, and sediment pockets serve as protected sites for breeding colonies, where litters can develop with minimal disturbance.
Physiological adaptations reinforce the suitability of these habitats. Rats possess a highly developed sense of smell and whisker sensitivity, enabling navigation in total darkness. Their incisors continuously grow, allowing them to gnaw through soft materials such as plastic, rubber, and thin metal, which facilitates access to hidden food caches and new tunnel sections.
Population dynamics are reinforced by reduced competition. The scarcity of other mammals that can thrive in such moist, confined spaces limits interspecific rivalry. Consequently, rat colonies can expand rapidly, especially when sanitation infrastructure provides consistent waste input.
In summary, underground drainage systems offer rats a combination of stable climate, abundant food, predator avoidance, structural shelter, and limited competition, all of which collectively support their persistence and growth in urban environments.