The Taj Mahal in Agra, India is an architectural icon and tourist destination. People are alarmed when its white marble turns green. What causes the green slime? A chain of events that involve insects. The green slime is waste, fly specks left by hordes of mating Chironomid midges of the genus, Goeldichironomous. The midge immatures live in nearby Yamuna River where they feed on algae. The midges excrete chlorophyll in their waste that colors the fly specks green. In the past, midge numbers were small and the small amount of droppings went unnoticed. The midge hordes with enough droppings to form a noticeable coating is a recent occurrence. The fly populations are much larger than in the past because the river has experienced large algal blooms. The algal blooms create plentiful food and habitat for the midges. The algal blooms are fed by dumping organic waste in the river and providing the algae with abundant fertilizer.
Work is underway to clean the green slime from the white marble. However, the longer term solution is to improve the water quality by reducing the level of pollutants entering the river and its tributaries. Pollution abatement could limit the algal blooms and reduce the swarms of midges to more historical and less damaging levels.