Last April, I spent a morning hiking along the San Pedro River, just NW of Bisbee, AZ; the caterpillars were astoundingly abundant. When I stopped, I could hear them munching on leaves all around--a surround-sound of crunching, the aural fecundity of spring.
Between Sierra Vista and Bisbee, the high grassland highway slowly slopes down to this cottonwood-lined river--one of the few free-flowing rivers left in the Desert Southwest. This ribbon of forest stretches from the Mexican border up towards the lower-elevation desert, providing a flyway for migrating birds and even habitat for the occasional jaguar (very rare).
In the late 1980's, this area was made a National Conservation Area, and it's a nice shady walk in what can often be sun-blasted country.