Roland Wauer"s Butterflies of the Lower Rio Grande Valley is the only field guide to cover all the reported species in what he calls the "number one butterfly area" in the country. His book includes a description of each species, when and where they can be found, a comparison of similar species, and additional remarks on natural history and nomenclature. Full-color photographs of almost all of the butterflies accompany the text. The book covers the area along the Rio Grande River in a band up to twenty miles north, beginning at the Gulf of Mexico and running 135 miles west to Falcon Dam. More like semitropical Mexico than anywhere else in the United States, the mild winters and hot, humid summers result in a rich diversity of plants and, therefore, butterflies, many of which do not occur farther north. The book begins with a guide to the twenty best sites for butterfly watching in the Valley, including the North American Butterfly Association"s International Butterfly Park, located near Bentsen-Rio Grande Valley State Park. The first facility of its kind, the park has a series of gardens designed to attract butterflies and, according to the author, "is destined to become the single most important butterfly viewing site in North America."