A Colony Two Million Strong
Inside caves of the Shwe Settaw Wildlife Sanctuary lives Myanmar's largest known bat colony. Over two million wrinkle-lipped free-tailed bats (Chaerephon plicatus) roost here. Each evening, they emerge to hunt insects, flying up to 50 kilometers from their roosts. This species is an important agent of pest control across Southeast Asia. A single bat can eat 50-100% of its body weight in insects every night. Studies on similar colonies in neighboring countries show they feed heavily on agricultural pests like plant-hoppers, which are known to cause significant damage to rice harvests. The collective appetite of the Shwe Settaw colony removes many tons of insects from the local environment nightly, providing an enormous, free pest-control service that benefits regional agriculture.
The Guano Archives
The floor of the bats' cave provides a unique scientific record. Centuries of accumulated bat droppings, or guano, have formed deposits reaching up to three meters deep. This dense layering of guano is a historical archive of ecological change. Scientists can analyze the insect fragments—bits of wings, legs, and exoskeletons—preserved in different layers of the deposit. This technique, often combined with DNA metabarcoding, allows researchers to identify the specific types of insects the bats consumed at different points in the past.
Changes in the bats' diet over time reveal changes in the landscape itself. For example, a shift in the insect record from forest-dwelling beetles to moths and planthoppers associated with rice farming would indicate a period of deforestation and agricultural expansion. By dating the guano layers using isotopes, scientists can correlate these dietary shifts with historical events and climate patterns. The guano, therefore, is waste; it is a detailed environmental history book written in the language of insect parts.