Trachycephalus venulosus is a large frog, with adult males 70 to 101 mm and adult females 93 to 114 mm in snout-vent length. The head is wider than long, with a round and blunt snout and medium-sized eyes. The tympanum is distinct and rather large, having a diameter 50 to 80% of the diameter of the eyes, and is larger in females than males. The body is robust. The dorsal skin is thick and glandular, with the highest concentration of glands near the back and sides of the head. Dorsal skin texture is strongly tuberculate in juveniles and may be tuberculate or smooth in adults. Ventrally, the skin is quite areolate on the throat, venter, and posteroventral area of the thighs. Fingers are short and robust and have large expanded finger discs, with the third finger disc being larger than the tympanum. Fingers are moderately webbed, while the toes have a large amount of webbing. The hand has an enlarged thenar tubercle pad and a bifid distal subarticular tubercle underneath the fourth finger; the palmar tubercle is lacking. The foot has an ovoid, average-sized inner metatarsal tubercle, a small, conical outer metatarsal tubercle and a very clear tarsal fold. Males have paired, lateral, expandable vocal sacs (unique among Costa Rican hylids), located behind the angles of the jaw when not inflated. Males also have a tan nuptial pad, lacking spines, on the base of the thumb. Bones are green, as in other frogs of the genus Trachycephalus, distinguishing this genus from other hylids (Savage 2002; this genus was formerly named Phrynohyas). Green bones are also present in centrolenid frogs.
This species can be distinguished from other treefrogs by its uniformly colored flanks and green bones, and the lack of dark vertical barring on the lip; additionally, males can be distinguished by the paired lateral vocal sacs, one on either side of the head behind the angle of the jaw (Savage 2002).
Dorsally, the frog is yellowish tan, tan, reddish brown, or pale gray in color. The ventral surface may be dirty light brown to cream. Adults typically have a large, dark olive tan to brown mark on the back that takes up almost the whole dorsal surface. Occasionally light spots are present on the dorsum, broken by transverse bands of the body color. Limbs tend to have transverse dark bars on the upper surfaces, though some individuals lack barring. Vocal sacs are pale or olive brown when inflated, but look dark brown or black when deflated. Irises are golden bronze with tiny splotches of black (Savage 2002).
Tadpoles of Trachycephalus venulosus are large, with a robust body measuring 41 mm in total length (Savage 2002). The tadpoles have a pond type body form with a forward facing mouth (anteroventral), eyes that are facing laterally and deep, high fins tapering to the end of the pointed tail (Zweifel 1964). Nostrils are anterolateral. The spiracle is lateral and on the left (sinistral) and the vent tube is medial (located in the middle of the body; Savage 2002). The younger tadpoles have complete beaks that gradually become poorly developed as the tadpole grows larger (Zweifel 1964). Oral discs are very small compared to the body, with the diameter being only about 44% of the body, and the edges are able to fold up make a shape like a triangle which closes the mouth (Zweifel 1964). Papillae are present, but not above the mouth, being located laterally and ventrally with the lowest row or two fragmented (Savage 2002). Beaks are finely serrated (Savage 2002). Tooth rows in the tadpoles may be 3-4 rows on the top and 4-6 rows on the bottom (Zweifel 1964; Savage 2002). Zweifel (1964) described a large space in the first row of upper denticles, and many spaces in the lower denticle rows (Zweifel 1964). Savage's (2002) description mentions A1 and A2 being present only laterally, and usually fragmented, with a slight median gap in the row just above the mouth (A2 or A3), and sometimes the row just below (P1) also with a narrow median gap. This tooth formula varies greatly from the typical Hyla larvae that have a 2/3 tooth row, and those species with more tooth rows do not have the gaps that T. venulosus has (Zweifel 1964).
Tadpoles have a brown dorsum and a creamy tan ventral surface with small brown splotches. The body has a brown stripe down the body lengthwise. Fins have small dark flecks of coloration and developed legs have a lengthwise dark stripe. The iris is a pale brown (Savage 2002).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Argentina, Belize, Bolivia, Brazil, Colombia, Costa Rica, Ecuador, French Guiana, Guatemala, Guyana, Honduras, Mexico, Nicaragua, Panama, Paraguay, Peru, Suriname, Trinidad and Tobago, Venezuela
This species has a wide range in Central and northern South America. It lives in lowland forests which may be dry, moist, or wet, at an elevation of 2-285 m (Savage 2002).
Life History, Abundance, Activity, and Special Behaviors
This is a nocturnal frog typically found perching on tree branches and vegetation while foraging at night. It shelters in bromeliads, tree holes, under tree bark of both living and dead trees, or in banana or heliconia sheaths during the dry season. During the rainy season, which is also the breeding season, these frogs are found near temporary ponds (Savage 2002).
Males call from the breeding site, while floating in the shallow water, their inflated lateral vocal sacs noticeable on either side of the head (Savage 2002). The advertisement call is described as a loud growl, repeated at regular, short intervals. Notes are repeated 42 to 69 times per minute with each note lasting between 230 and 400 ms (Savage 2002). The dominant frequency is from 1.39 to 2.5 kHz, and the call has 12 to 14 harmonics (Duellman 1970; Lee 1996). Males can be heard calling in groups of 5-10, or rarely in larger groups of 20-40 (Gottsberger and Gruber 2004). Most calls occur during the first night of explosive breeding (Gottsberger and Gruber 2004).
Trachycephalus venulosus also has a distinct distress call. The call starts with a 'squeaklike' sound that probably comes from constricted airways, followed by three bursts of sound lasting between .29 and .38 seconds (Leary and Razafindratsita 1998). Analysis of a recorded call shows that the sound bursts were separated by intervals of 1.405 and 3.014 seconds (Leary and Razafindratsita 1998). The first two sound bursts had a fundamental frequency of 260 Hz with a dominant frequency of 3.27 to 5.67 kHz while the third had a higher dominant frequency of 4.75 and 7.08 kHz (Leary and Razafindratsita 1998). After the distress call, many frogs were observed coming out of hiding in trees and going towards the calling frog; shortly after the frog escaped, the responding frogs returned to their hiding places (Leary and Razafindratsita 1998).
Breeding is explosive after heavy rains (Savage 2002). After amplexus occurs in the water, females lay eggs as a film on the water surface, with the film covering a total of 1.5 square meters (Zweifel 1964). Eggs were recorded to be developing at temperatures ranging from 27 to 33 degrees Celsius (Zweifel 1964). The eggs, which have a diameter of 3.5 mm, hatch after one day into free-living tadpoles at stage 18, with a length of 3.8 to 4.4 mm (Savage 2002). Metamorphosis into an adult takes between 37 to 47 days (Zweifel 1964; Pyburn 1967). Some aspects of larval coloration are retained initially, such as a dark leg stripe and green bones, but are quickly lost within a few days and replaced by the full adult coloration (Savage 2002).
The tadpoles have very large gills, most likely as an adaptation to living in warm water with a low oxygen level (Zweifel 1964). Tadpoles have been observed to spread out the gills at the surface of the water (Zweifel 1964). Combined with the large lungs, these tadpoles are well suited for life in small ponds (Zweifel 1964). The larvae feed by scraping surfaces underneath the water (Savage 2002). In the wild, tadpoles consume planktonic algae (Rossa-Feres et al. 2004). In the laboratory, tadpoles were fed successfully with canned spinach and sometimes boiled lettuce (Zweifel 1964).
Adults of this species have granular glands in the skin, concentrated in the dorsal pustules and in the interorbital, occipital, supratympanic, and anterior dorsal areas (McDiarmid 1968). These glands can secrete a large amount of sticky white, volatile, poisonous, alkaline, water-insoluble mucus, when the frog is handled (Savage 2002). The glands along the side of the neck look normal during the wet season (from late June onwards), but in the dry season (February and March) they become greatly enlarged and can cover most of the tympanum (McDiarmid 1968). The mucus deters predators; in one documented case, a frog released a large amount of milky white mucus on an attacking snake's head, causing the snake to release the frog because it was so covered in the thick mucus it could not close its mouth or see (Leary and Razafindratsita 1998). The mucus is also sticky and water-insoluble, so frogs may make use of it to combat desiccation during the dry season by reducing water loss through the skin (Savage 2002). Some may even line tree holes with the secretion to help keep moist, as is the case for South American members of this genus (Savage 2002; Veillardi 1948).
These frogs also have a highly developed ability to parachute from trees (Cott 1926). One was observed gliding for 27 m, after being dropped from a height of 43 m (Cott 1926). The frog was not simply falling, because it consistently descended with the back facing upwards and the legs spread out laterally (Oliver 1951).
Trends and Threats
Currently, this species is listed as Least Concern (IUCN 2006). In one study, no individuals of Trachycephalus venulosus were found over a 3 year period, but since the previous study had only found 3, it is not necessarily declining (Eterovick et al. 2005). More likely it has always been present in very low numbers in that area of Brazil (Eterovick et al. 2005). Furthermore, this species is very widespread in Central and South America, so the populations there are most likely not in any danger of declines (IUCN 2006).
Relation to Humans
This frog produces sticky, insoluble, noxious secretions that cause severe reactions, ranging from irritation, swelling, and pain to temporary blindness if the secretions end up in the eyes or on any mucous membrane (Savage 2002). It is called the 'pepper treefrog' in Belize because it is thought to cause sneezing (Meyer and Foster 1996).
This species was treated as Phrynohyas venulosa in Savage (2002).
The karyotype is 2N = 24; all chromosomes are metacentric or subtelocentric (Bogart 1973).
A Spanish-language species account can be found at the website of Instituto Nacional de Biodiversidad (INBio).
Bogart, J. P. (1973). ''Evolution of anuran karyotypes.'' Evolutionary Biology of the Anurans: Contemporary Research on Major Problems. J. L. Vial, eds., University of Missouri Press, Columbia.
Cott, H. B. (1926). ''Observations on the life-habits of some batrachians and reptiles from the lower Amazon: and a note on some mammals from Marajo Island.'' Proceedings of the Zoological Society of London, 1926, 1159-1178.
Eterovick, P. C., Carnaval, A. C. O. Q., Borges-Nojosa, D. M., Silvano, D. L., Segalla, M. V., and Sazima, I. (2005). ''Amphibian declines in Brazil: an overview.'' Biotropica, 37(2), 166-179.
Gottsberger, B., and Gruber, E. (2004). ''Temporal partitioning of reproductive activity in a neotropical anuran community.'' Journal of Tropical Ecology, 20, 271-280.
IUCN, Conservation International, and NatureServe. (2006). Global Amphibian Assessment: Trachycephalus venulosus. www.globalamphibians.org. Accessed on 12 May 2008.
Leary, C., and Razafindratsita, V. (1998). ''Attempted predation on a hylid frog, Phrynohyas venulosa, by an indigo snake, Drymachon corais, and the response of conspecific frogs to distress calls.'' Amphibia Reptilia, 19, 442-446.
McDiarmid, R. W. (1968). ''Populational variation in the frog genus Phrynohyas Fitzinger in Middle America.'' Contributions in Science of the Natural History Museum of Los Angeles County, 134, 1-25.
Meyer, J. R. and Foster, C. F. (1996). A Guide to the Frogs and Toads of Belize. Krieger Publishing Company, Malabar, Florida.
Oliver, J. A (1951). '''Gliding' in amphibians and reptiles, with a remark on an arboreal adaptation in the lizard, Anolis carolinensis carolinensis Voigt.'' The American Naturalist, 85(822), 171-176.
Rossa-Feres, D. C., Jim, J., and Fonseca, M. G. (2004). ''Diets of tadpoles from a temporary pond in southeastern Brazil (Amphibia, Anura).'' Revista Brasileira de Zoologia, 21(4), 745-754.
Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago and London.
Vellard, J. (1948). ''Batracios del chaco argentino.'' Acta Zoologica Lilloana, 5, 137-174.
Zweifel, R. G. (1964). ''Life History of Phrynohyas venulosa (Salientia: Hylidae) in Panama.'' Copeia, 1, 201-208.
Written by Kristina Prus (kprus AT fas.harvard.edu), Harvard
First submitted 2008-05-14
Edited by Kellie Whittaker (2009-11-02)
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