The bats started making their home under the red roof during Khmer Rouge rule, when the museum was vacant. By the early 1990s, curators were desperate to evict them as droppings—up to a ton a month—coated the artifacts below and threatened to collapse the second-floor ceiling. A putrid stench distracted gallery patrons, and on one memorable occasion, bat lice in the air elicited an allergic reaction from a visiting Thai princess.
But conservationists protested. The four species of bats living at the museum are unusual: scientists say the Cambodian Free-Tailed Bat, in particular, can be found nowhere else in the world. In addition, the museum's 2 million bats were messy but useful: they were credited with eating an estimated 17 tons of insects each night, helping reduce mosquito-borne malaria. So the government scrapped its plan to eradicate the bats. (Another factor was that the museum makes $250 a month selling bat guano.) A second, wooden ceiling, installed in 1995, failed to keep the excrement out of the gallery, so the New York City-based Wildlife Conservation Society is trying to raise $1 million to replace it with a concrete one.
Museum director Khun Samen resents the attention the bats receive—he would rather have the public focus on his collections, a centerpiece of which is the original Leper King statue from the Angkor Thom region, rare partly because the ancient sculpture is nude. Still, when travelers trade tips about the National Museum on the Internet, they usually describe how best to view the dusk drama. Which, of course, drives the administration batty.