Adult: Species description based on Grant (2004). A small frog, males to 27 mm, females to 28 mm. The third finger is swollen in adult males. Dorsal: The dorsal surface is dark brown with no lighter dorsolateral striping. Ventral: The ventral surface differs between males and females. In males, the ventral surface is white or has some faint mottling. In females, the throat has extensive darker mottling not typically present in males. The bright white vocal sac of males may be a visual signal of territorial defense (Wells 1980a). Concealed surfaces: The lateral surface is dark brown, interrupted by a thin white line extending from the groin to halfway to the armpit along the side of the body. Distinguishing characteristics: Bright gold or yellow coloration is present in the armpit, groin, and concealed surfaces of the hind limbs. Extremities: The feet are moderately webbed.
Breeding season: In a January to November study, C. panamansis was reproductively active in every month except April, but reproduction slowed in the wettest months late in the rainy season (Wells 1980a). Reproduction peaks in May and June (Wells 1980a). Egg: Eggs are laid on land, and then females carry tadpoles (up to 40 at one time) on their backs to streams to continue development (Wells 1980a & b). Some tadpoles remain on the backs of females for up to 9 days (Wells 1980a & b). During that time, they gain length by feeding on yolk reserves, and possibly by feeding from the female's back when she enters small pools of water (Wells 1980b). Metamorph juvenile: Frogs reach maturity 4-6 months after metamorphosis (Wells 1980a). The bright yellow coloration present in adults is undeveloped in juveniles (Grant 2004).
Habitat: Lowland rainforest to 800 m. Ecology: Colostethus panamansis populations have likely begun to decline east of the Panama Canal due to outbreaks of chytrid fungus (Woodhams et al 2008). Call: A short trill (Wells 1980a). Colostethus panamansis also produces an aggressive call, a long peep (Wells 1980a). Close encounters elicit an aggressive chirp (Wells 1980a). Behavior and communication: Colostethus panamansis defends territories (Duellman 1966, Wells 1980a). Both males and females show aggressive behavior, and territorial defense is strongest in the dry season, when suitable habitat and resources are scarce (Wells 1980a). This species even shows aggression towards other species, particularly Colostethus pratti (Wells 1980a). An excellent description and photographs of aggressive, courtship and reproductive behavior can be found in Wells (1980a). Type locality: El Valle de Anton in the northwestern corner of the Province of Panama