The 81 species of ants collected in the Chisos Mountains, Texas showed high diver- sity and low dominance. Twelve taxa were new records for Texas. Characteristic ant assemblages were recognized for lechuguilla grasslands, canyons, pinyon-juniper-oak and high forest associa- tions. The Chisos offer an island of woodland in north-south distribution of ant species, and the availability of these woodlands may result in the recorded large number of ant species per unit area. Most species prefer relatively thick canopy, some leaf litter, a gentle slope, and nest under rock or with a crater. The Chisos Mountains rise from the succulent Chihuahuan Desert within a few miles of the Big Bend of the Rio Grande, in the Big Bend National Park, Brewster County, Texas. These mountains are historically important, acting as landmarks and camping sites for both Apaches and Commanches, for Spanish explorers, and for Mexican and American settlers and smugglers. They are ecologically unique, for within their small area (approximately 50 mi2 or 130 km2) the lower woodland of pinyon-juniper- oak gives way to a higher forest of ponderosa pine, Douglas fir and Arizona cypress. A similar habitat does not occur for several hundred miles to the north, and fifty miles to the south. The Chisos are a mountain island on a north-south distribution pathway for forest or high canyon species. Below the forest and the woodland lie the desert grassland belt, character- ized by grass and sotol, and, at the lowest elevations the shrub desert leading to the river flood plain. The high forest (Moist Chisos Woodland, 1768-2195 m) located at Boot Canyon is characterized by Douglas fir, Arizona cypress and ponderosa pine. The woodland (1128-2377m) below is separated into two vegetational types. The lower washes include some grassland species, but are character- ized by black walnut and Mexican buckeye. The deeper, higher canyons are characterized by several species of oak and by Texas madrone. The most extensive vegetational type of the woodlands is the open pinyon-juniper-oak association. Several species of grasses are present. The lechuguilla-sotol-grass association (975-1676 m) forms a belt below the woodland of the Chisos. Sotol, cacti, lechuguilla, nolina and Big Bend agave are typical of this lowest portion of the mountains. Below this associ- ation lies the Chihuahuan Desert. For thorough discussion of the ecological communities of this area, see Taylor et al. (1944), Denyes (1956) and Wauer (1971). Wauer's analysis of communities for the distribution of birds fits best the data in the present study. A bibliography of all published and some typescript papers on bio- logical research done in the Big Bend National Park is included in Wauer