Hyloxalus insulatus (Duellman 2004)

Males of this moderately small species of Colostethus attain a snout-vent length of 22.2 mm, females, 26.0 mm. The discs on the fingers and toes are expanded, half again the width of the penultimate phalange. Finger I is longer than Finger II, and Finger III is not swollen in males. Lateral fringes are present on the fingers and toes. An outer tarsal fold and tarsal tubercle are absent; the inner tarsal fold is curved and distinct on the distal half of the tarsus. The toes are webbed basally. The dorsum is reddish brown with dark brown middorsal marks, the anterior two or three of which are broadly chevron-shaped, and the posterior two usually are round, quadrangular, or elongate. The upper lips and proximal dorsal surfaces of the upper arms are white; the rest of the forearms are brown with diffuse grayish white mottling. Dorsolateral and ventrolateral stripes are absent. The oblique lateral stripes are creamy white; the flanks are gray mottled with brown. The dorsal surfaces of the thighs are dull brown with darker brown markings ranging from irregular spots to transverse bars; the anterior surfaces of the thighs are brown with a narrow creamy-white longitudinal stripe connected to an oblique lateral stripe in the groin. The throat is gray with a pair of black spots; the belly is creamy white, and the ventral surfaces of the hind limbs are pale gray with a diffuse, dull orange spot on the proximal ventral surface of each shank. The digital scutes are white to pale gray, in contrast to the brown digits; the iris bronze is with black flecks. A median lingual process is absent, and the testes are white (Duellman 2004). The tadpole at Stage 34 has a body length of 13.0 mm and a total length of 38.8 mm. The body is globular, wider than high. The snout is rounded in dorsal view and in profile. The moderately large eyes are situated and directed dorsolaterally and not visible from below. The spiracle is sinistral, short, and attached for its entire length to the body wall; the spiracular opening is directed posterodorsally well below midline at about midlength of the body. The cloacal tube is short, dextral, and attached to the ventral fin. The caudal musculature is robust and about equal in height throughout the proximal half of tail, whereupon it diminishes gradually to a pointed terminus. The dorsal fin originates on the base of the caudal musculature, reaches its greatest height at about midlength of the tail, and diminishes to a bluntly rounded tip; the ventral fin originates on the body wall and reaches its greatest height just posterior to the midlength of the tail. The oral disc is directed anterolaterally. The median half of the anterior labium is bare; elsewhere the labia bear a single row of slender, pointed marginal papillae. The labia are infolded laterally; a few small, round papillae are present in the folds. The jaw sheaths are moderately slender and coarsely serrate; the anterior sheath forms a broad arch, and the lower sheath is broadly V-shaped. The labial tooth row formula is 2(1)/3; A2 is the longest, P3 the shortest, and other rows equal in length. The body is olive brown, and the tail is brown with olive flecks; the iris is pale bronze. Recently metamorphosed young are colored like adults except they are slightly paler and lack dark spots on throat.

Hyloxalus insulatus inhabits the middle Río Marañón Valley in northern Peru, where it is known from elevations of 1260 to 2600 m. This region supports dry scrub forest, which in some areas is dominated by cacti. A few small streams cascade down the steep slopes from the adjacent highlands of the Cordillera Occidental and Cordillera Central. This species occurs around small streams and associated waterfalls, or seepage areas.

Hyloxalus were found by day on and under rocks adjacent to streams and especially in spray zones of waterfalls; others were under rocks in seepage areas or adjacent to small spring-fed streams. Tadpoles were found in quiet pools in the streams.