The terciopelo (Bothrops asper)[note 1] is a species of pit vipers, found from north-east Mexico to northern South America.

The specific epithet, asper, which is a Latin word meaning 'rough' or 'harsh', may allude to the species' keeled dorsal scales.

[8] Some of the common names applied to this snake are terciopelo ("velvet" in Spanish), fer-de-lance,[3] mapepire balsain (Trinidad), carpet labaria (Guyana), barba amarilla (Guatemala, Honduras, Nicaragua; "yellow beard"), equis (Ecuador and Panama; "x"),[9] talla equis , mapaná (Colombia), mapanare (Venezuela), nauyaca (México; from Nahuatl nahui, four, and yacatl, nose; "four noses"),[10] and yellow-jaw tommygoff (Belize)."

[11] In their seminal opus on the venomous reptiles of the Western hemisphere, Campbell & Lamar stated: "The name fer-de lance, widely used in North America with reference to B. asper and B. atrox, has no legitimate origin of use in regions inhabited by this snake.

"[3] In an effort to establish standardized names for the amphibians and reptiles of North America, the Society for the Study of Amphibians and Reptiles (SSAR), a not-for-profit organization and one of the largest international herpetological societies, applied the following nomenclature:[4][5] In recent decades, herpetologists have preferred the name 'terciopelo' for Bothrops asper,[16][17][18][19] although the term fer-de-lance is still common in popular usage.

The ventral side is yellow, cream, or a whitish gray, with dark blotches that are more frequent closer to the posterior end.

As a result, great confusion between it and other related species, most notably Bothrops atrox, which is similar in color but usually has yellow or rust-like tones and rectangular or trapezoidal blotches.

[3] It is found on the Gulf - Atlantic versant of eastern Mexico as far north as the state of Tamaulipas, southward through the entire Yucatán Peninsula extending into Central America, including Guatemala, Belize, Honduras, Nicaragua, Costa Rica and Panama.

[2][22] This is mostly a lowland species that, in Mexico and Central America, occurs from about sea level to 1,200 to 1,300 meters (3,900 to 4,300 ft) altitude.

[3] According to Campbell and Lamar (2004), its range in Ecuador extends as far south along the Pacific coast as El Oro Province and the Vilcabamba area of the Río Catamayo Valley.

[3] This species is reported to occur from seven (Bolívar, Carchi, Chimborazo, Esmeraldas, Guayas, Los Ríos and Pichincha) of the fourteen provinces along the Pacific slope of Ecuador.

[3] B. asper occurs throughout the inter-Andes valleys of Colombia across the Caribbean coastal plain through central Venezuela north of the Orinoco as far east as the Delta Amacuro region.

[3] Due to the casual and informal application of the name "Fer-de-lance" being applied to any number of species of Latin America pit vipers in the genus Bothrops, there is much confusion and misunderstanding, particularly in popular literature, as to proper nomenclature.

[14][15] This species likes moist environments, and occurs in most life zones located at low or middle elevations (up to 600 metres (2,000 ft)), excluding those with strong seasonal dry periods.

This species is often found near rivers and streams, basking in the sun during the day and lying still while well camouflaged in leaf litter or under forest cover waiting to ambush prey such as rats and mice that come within range during the night.

In a review of bites from this species suffered by field biologists, Hardy (1994) referred to it as the "ultimate pit viper".

[22] Just a few of the documented ectothermic prey items include: small to moderately-sized centipedes (specifically Scolopendra angulata), beetles (Coleoptera), grasshoppers (Orthoptera), flies (Diptera), hemipterans (Hemiptera), ants (Formicidae), crayfish (Astacidea), eels (Synbranchus); caecilians (Dermophis), frogs (Eleutherodactylus, Leptodactylus, Lithobates, Pristimantis, Rhinella, Smilisca), toads (Rhinella), amphisbaenians (Amphisbaena), lizards (Alopoglossus, Ameiva, Anolis, Ctenosaura, Gonatodes), and snakes (Bothrops, Dipsas, Erythrolamprus, Ninia).

[26] Endothermic prey species include: bay wren (Cantorchilus nigricapillus), grey-headed tanager (Eucometis penicillata), wren (Troglodytes), blue-black grassquit (Volatinia jacarina), Central American woolly opossum (Caluromys derbianus), common opossum (Didelphis marsupialis), Desmarest's spiny pocket mouse (Heteromys desmarestianus), dusky rice rat (Melanomys caliginosus), black rat (Rattus rattus), Rothschild's porcupine (Coendou rothschildi), Brazilian cottontail (Sylvilagus brasiliensis), and least shrew (Cryptotis parva).

[22][27] The timing of the reproductive cycle and the litter size of this species vary according to location: in some parts of Costa Rica, for example, it is more prolific than in others.

It is considered the most dangerous snake in Costa Rica, responsible for 46% of all bites and 30% of all hospitalized cases; before 1947, the fatality rate was 9%, but this has since declined to almost 0% (Bolaños, 1984), mostly due to the Clodomiro Picado Research Institute,[30] responsible for the production of snake antiophidic sera (which are also exported to other countries in Latin America and Africa) and scientific research on serpents and their venoms, as well as educational and extension programs in rural areas and hospitals.

[31] Bite symptoms include pain, oozing from the puncture wounds, local swelling that may increase for up to 36 hours, bruising that spreads from the bite site, blisters, numbness, mild fever, headache, bleeding from the nose and gums, hemoptysis, gastrointestinal bleeding, hematuria, hypotension, nausea, vomiting, impaired consciousness and tenderness of the spleen.

[21] The venomous bite of B. asper has been suggested to have been a factor in the choice of certain Mayan settlements, such as Nim Li Punit, Belize Central America, where the thick jungle inhabited by these snakes was used as a defensive boundary.