Bothrops atrox — also known as the common lancehead, fer-de-lance, barba amarilla[3] and mapepire balsain — is a highly venomous pit viper species found in the tropical lowlands of northern South America east of the Andes, as well as the Caribbean island of Trinidad.

[4] The common lancehead was one of the many reptile and amphibian species described by Carl Linnaeus in the landmark 1758 10th edition of his Systema Naturae, where it was given the binomial name Coluber atrox.

In Ecuador and Panama, these x-like markings have led to the snake simply being referred to as equis (the Spanish name of the letter 'x').

The body markings are highly variable, as is the degree of contrast: in some specimens the pattern is very well defined, while in others it may be virtually absent.

In general, however, the body pattern consists of a series of dorsolateral blotches, rectangular or trapezoidal in shape, which extend from the first scale row to the middle of the back.

They also have pale borders, which in some cases may be prominent, and may be invaded from below by tan or gray pigment, occasionally dividing them into pairs of ventrolateral spots.

The head usually does not have any markings other than a moderately wide postocular stripe that runs from behind the eye back to the angle of the mouth.

The main diet includes mostly small mammals (such as rodents and opossums) and birds, but also frogs, lizards, smaller snakes, fish, centipedes, and tarantulas.

At birth, the young are about 30 cm (12 in) in total length, more brightly colored than adults, and have yellow or beige tails.

Three species of the Neotropical pit viper Bothrops atrox group were confirmed to undergo facultative parthenogenesis on the basis of captivity information and by the use of molecular markers (heterologous microsatellites).

Their venom is hemorrhagic, damaging the vascular endothelium and consuming coagulation factors in a mechanism known as “venom-induced consumption coagulopathy”.

[21] The Common lancehead has an LD50 of 1.1 to 4.9 mg/kg, the venom of juveniles is more inflammatory, lethal, hemorrhagic and kills more quickly than that of adults, people bitten by neonates are more likely to develop coagulopathy.

[citation needed] The enzyme reptilase (batroxobin), derived from this snake's venom, is used in modern medical laboratories to measure fibrinogen levels and blood coagulation capability.