The Fer-de-lance is a highly venomous pit viper species found from southern Mexico to northern South America. It is the most dangerous snake of Central and South America and is the main cause of fatal snakebite incidents within its range. These snakes can be distinguished by their broad, flattened heads which are set apart from the rest of their bodies. Their head is light to dark brown or even black in color. The underside is most often pale yellow. This species has different patterns and colors on its dorsal and ventral. The ventral side is yellow, cream, or a whitish-gray, with dark blotches that are more frequent closer to the posterior end. Some individuals may have a yellow zig-zag-shaped line on each side of the body. There is a great variety of colors on their dorsal side: olive, gray, light brown to dark brown, tan or sometimes nearly black. Females have thick, heavy bodies and grow significantly larger than males. They also have heads two or three times the size of males relative to their size and proportionally bigger fangs (typically 2.5 cm), as well.
Fer-de-lances are found in eastern Mexico and Central America, including Guatemala, Belize, Honduras, Nicaragua, Costa Rica, and Panama. An isolated population occurs in southeastern Chiapas (Mexico) and southwestern Guatemala. In northern South America, these snakes are found in Colombia, Ecuador, Guyana, and Venezuela. Fer-de-lances like moist environments. They can be found in the premontane forest in Costa Rica, the cloud forest of Guatemala and Mexico, or the lower montane wet forest in the Caribbean Region of Colombia and Ecuador. They chiefly inhabit tropical rainforest and evergreen forest, but will also occur in drier areas of tropical deciduous forest, thorn forest, and pine savannah near lakes, rivers, and streams.
Fer-de-lances are nocturnal and solitary snakes. They are less active in colder and drier periods. They are 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. Juveniles are often semiarboreal, and even adults can sometimes be seen in bushes and low trees. Juveniles also exhibit caudal luring, a use of their differently colored tail tips to lure prey. Although both males and females display this behavior, only males have bright coloured tail tips. These snakes are excitable and unpredictable when disturbed. When cornered or threatened, Fer-de-lances can be very defensive and may exhibit an S-coiled defense display. They can, and often will move very quickly, usually opting to flee from danger, but are capable of suddenly reversing direction to vigorously defend themselves. Adult specimens, when cornered and fully alert, are dangerous. When cornered or threatened, Fer-de-lances can be very defensive and may exhibit an S-coiled defense display.
Fer-de-lances are carnivores and feed on birds, amphibians, reptiles, and small mammals, mainly rats, and mice. Juveniles consume small frogs, lizards, and even large insects.
Fer-de-lances have are polyandrous which means that females mate with more than one male during mating season. The breeding season of these snakes varies according to location. In some parts, mating takes place between September and November, with females giving birth between April and June. Some populations may mate in March, and give birth in September-November. The average number of offspring is 5-86 live young. In both populations, gestation time ranged from 6 to 8 months. Snakelets are born fully-developed and don't need parent care.
The main threat to Fer-de-lances is habitat loss due to deforestation, agriculture, and urbanization. These snakes also suffer locally from environmental changes and the decline of their prey species.
Fer-de-lances are important predators in the ecosystem they live in as they control populations of species they prey on.