Mexican free-tailed bats, Tadarida brasiliensis, occupy a wide variety of habitats, ranging from desert communities through pinion-juniper woodland and pine-oak forests at elevations from sea level to 9,000 feet or more. The largest U.S. populations of free-tailed bats live in the West, with the densest concentrations found in Texas where they form maternity colonies numbering in the millions. They are found throughout Mexico and most of the western and southern U.S. The largest maternity colonies are formed in limestone caves, abandoned mines, under bridges, and in buildings, but smaller colonies also have been found in hollow trees. It is estimated that 100-million Mexican free-tailed bats come to Central Texas each year to raise their young. Nursing females require large quantities of insects that are high in fat, which they obtain by consuming egg-laden moths.
The 100 million free-tailed bats living in Central Texas caves consume approximately 1,000 tons of insects nightly, a large proportion of which are agricultural pests. Researchers using Doppler weather radar watch emerging bats ascend to altitudes of 1,000-10,000 feet to feed on migrating cotton boll worm moths, army cut-worm moths, and other costly agricultural pests that migrate north from Mexico. These migratory moths hopscotch across the country each year, reaching rich agricultural land as far north as the Canadian border. The cotton boll-worm moth (a.k.a. corn ear-worm moth) alone, costs American farmers a billion dollars annually. Although the ecological and economic impacts of large colonies are most obvious, even small colonies of bats can significantly impact local insect populations. Mexican free- tailed bats also consume enormous quantities of insects over woodlands and forests, likely including many additional pests. (Source: Bat Conservation International)
Mexican free-tailed bat By U.S. Fish and Wildlife Service Headquarters - Uploaded by Dolovis, Public Domain, Link
Map By PraiseTheAlmightyHelixFossil - Own work, CC BY-SA 3.0, Link