Hyla regilla is a small frog, about 3/4 to 2 inches, that has expanded toe disks and a black eye-stripe (Stebbins 1985). The stripe runs from the tip of the snout posteriorly through the eye to the forelimb insertion (Grismer 2002). The stripe is hard to see in dark frogs, but it is always present. The dorsal coloration is highly variable, and could be gray, tan, green, brown, or black, and it may change color from dark to light within a few minutes. It often has a triangular dark spot on the head and dark spots on the back and legs, and the clarity of these spots changes as the frog changes its color phase. Its limbs are crossbanded or blotched with dark color, and the posterior has a yellow or orange color, especially on the under surfaces of the limbs, the rear of the femur, and in the groin. Males have a wrinkled and dusky throat. When the males vocal sac is deflated, often 8 to 12 longitudinal folds are present (Stebbins 1985). It has webbed hind toes with a margin of the web between successive toes. Skin is usually smooth with a few tubercles but occasionally quite rough. It has a round tympanum, that is anywhere from 1/4 to slightly over 1/2 the size of the eye opening, located in the eye stripe. The thenar tubercle is elongated and ovoid, while the palmar tubercle is made of 3 small, closely associated tubercles totaling the size of the thenar tubercle (Stebbins 1951).
A similar species, Hyla cadaverina, the California Treefrog, usually does not have an eye-stripe, has larger toe pads, and more fully webbed hind toes. H. cadaverina is also rarely green. Another similar species, Hyla eximia, the Mountain Treefrog, the eye-stripe extends beyond the shoulder and webbing is reduced (Stebbins 1985).
It is certain that there are isolated populations of H. regilla in many unexplored canyons of the Sierra la Giganta that harbor hidden permanent springs. In some water systems west of San Ignacio, there is evidence that H. regilla is being displaced by the bullfrog, Rana catesbeiana (Grismer 2002).
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- Grismer, L. L. (2002). Amphibians and Reptiles of Baja California. University of California Press, Berkeley.
- Livezey, R. L., and Wright, A. H. (1947). ''A synoptic key to the salientian eggs of the United States.'' American Midland Naturalist, 37, 179-222.
- Smith, R.E. (1940). ''Mating and oviposition in the Pacific Coast tree toad.'' Science, 92(2391), 379-380.
- Stebbins, R. C. (1972). Amphibians and Reptiles of California. University of California Press, Berkeley, Los Angeles, London.
- Stebbins, R. C. (1985). A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.
- Stebbins, R.C. (1951). Amphibians of Western North America. University of California Press, Berkeley.