Green and black stains have again started appearing on the marble walls of the Taj Mahal due to insect attack. The Archaeological Survey of India's (ASI) superintending archaeologist (Agra circle) Vasant Swarankar said the issue has become a permanent problem as filth in the Yamuna river provides a perfect breeding ground for insects to breed.

from Times of India https://timesofindia.indiatimes.com/city/agra/insects-invade-taj-again-leave-green-black-stains-on-marble/articleshow/70368723.cms