People
The last place you would think to find people living is a sewer. But many homeless people are driven by freezing temperatures into underground pipes to survive. In Mongolia, some homeless people climb through manholes to find shelter. They use cardboard, trash, heating pipes and clothing to keep warm. In 2004, officials in Italy found 100 immigrants living in a sewer system below Rome's railway system. Many were children who had escaped from Afghanistan.
Rats
Rats live outdoors and can burrow into sewers. They are good swimmers, resilient and excellent scavengers, making sewers a luxurious home for them. The sewer system is also a convenient track for them to follow. But rats, which can burrow a hole more than 3 inches across, can cause structural damage to sewers and spread disease.
Worms
In North Carolina, annelid worms were filmed living in a sewer. This was unusual because normally Tubifex lives in soil and along the edges of polluted streams. However, in this instance, the worms had coiled around each other to stay alive and were feeding off the sewer pollution.
Bacteria and Organisms
Numerous types of organisms and bacteria live in sewers. One of the most significant of these is the fecal coliform bacterium. It lives in the intestinal tracts of animals and ends up in sewers when it is passed. Presence of coliform bacteria can lead to the development of pathogenic bacteria, viruses and parasites.
Alligators and Snakes
It is a bit of a myth that alligators and snakes live in sewers. However, there are reports of people encountering reptiles, frogs and snakes in their toilets. For example, in New South Wales, Australia, frogs were blamed for blocking up the cisterns of toilets. In the United Kingdom, it was reported that a boa constrictor popped out of a toilet after escaping from its owners and living in the sewers for three months. Snakes in toilets have also been reported in Singapore and Malaysia.