American snout butterfly
Libytheana carinenta. The reason for the common name is evident. This is the only North American species of the snout butterflies, an ancient subfamily of Nymphalidae (Nymphalidae are butterflies distinguished by having reduced or absent forelimbs, hence apparently having only four legs.) In the southwest United States snouts often appear in enormous numbers.
The flowers are bee-brush, Eysenhardtia texana.
Photo taken at McKinney Falls State Park near Austin.