As of 2010, wild axolotls were near extinction due to urbanization in Mexico City and consequent water pollution, as well as the introduction of invasive species such as tilapia and perch. Axolotls are used extensively in scientific research due to their ability to regenerate limbs. Axolotls were also sold as food in Mexican markets and were a staple in the Aztec diet. Just a month later, two wild ones were spotted in a network of canals leading from Xochimilco. The city is working on conserving axolotls by building «axolotl shelters» and conserving remaining and potential habitats for the salamanders