Reptiles
Bushmaster
Lachesis muta · also called South American bushmaster, pit viper, mapepire
The bushmaster is the giant of the American pit vipers — up to three and a half metres of heavy, rough-scaled, patterned snake, the longest venomous serpent in the Western Hemisphere and the longest viper in the world. It lies in wait on rainforest trails for weeks at a time, and, alone among the big vipers of the Americas, it lays eggs and stays to guard them.
Overview
Bushmasters live in remote, undisturbed lowland rainforest in the Amazon basin and Brazil’s Atlantic Forest, with related species reaching Central America. They are nocturnal, solitary, and terrestrial, hunting rodents — spiny rats especially — along the forest floor. They occur at naturally low densities and are rarely seen.
The ultimate ambusher
A bushmaster hunts by sit-and-wait taken to an extreme: it may stay coiled in the same spot beside a trail or log for two to three weeks, perfectly still and camouflaged, waiting for prey to pass. Like all pit vipers it detects warm animals with heat-sensing pits on its face, and it vibrates its tail in the leaf litter when alarmed, making a dry rattle despite having no rattle.
The egg-layer
Nearly every viper gives live birth — the bushmaster is one of the few that lays eggs. The female coils around a clutch of 5–20 eggs in a burrow and guards it for the ~10-week incubation, a rare degree of snake parental care.
The venom
A bite delivers a large dose of hemotoxic venom through long fangs, causing severe pain, swelling, bleeding, a drop in blood pressure, and kidney failure. Historically bushmaster bites had a high fatality rate; modern antivenom improves it. Bites are uncommon because the snake is remote, nocturnal, unaggressive, and motionless.
Status
The bushmaster is Vulnerable and declining. It is a primary-forest specialist that does not tolerate logging or fragmentation and is one of the first snakes to disappear from disturbed rainforest, on top of being killed on sight.
Bushmaster: common questions
How big does a bushmaster get?
Most adult bushmasters are 2 to 2.5 metres, but they can exceed 3 metres, and the largest reliable record is around 3.6 metres. That makes the bushmaster the longest venomous snake in the Americas (longer than any rattlesnake or coral snake) and the longest pit viper anywhere in the world — only the king cobra, among all venomous snakes, is regularly longer. It is a heavy-bodied snake with a large triangular head, keeled scales that give it a rough texture, and a distinctive raised ridge of scales down the spine.
Is it true a bushmaster lays eggs? Vipers give live birth.
Almost all vipers, including all the other American pit vipers, give birth to live young. The bushmaster is one of a small handful of exceptions — it lays eggs. A female produces a clutch of roughly 5 to 20 eggs in a burrow (often an abandoned mammal burrow) and then coils around them, guarding the clutch and staying with it for the whole incubation of about ten weeks. This parental attendance is itself unusual for a snake. Why the bushmaster and a few relatives retained or re-evolved egg-laying while their close cousins went to live birth is not fully understood.
How dangerous is a bushmaster bite?
Very, but bites are rare because of where and how the snake lives. Its venom is delivered in a large quantity through long fangs and causes intense local pain, massive swelling, blistering, bleeding from the bite and internally, a dangerous drop in blood pressure, and acute kidney failure. Historical case reports gave bushmaster bites a high fatality rate, though modern antivenom and intensive care have improved outcomes substantially where they are available. The reason bites are uncommon is that the bushmaster lives in remote primary rainforest, is nocturnal, is not aggressive, and spends most of its time motionless and camouflaged; most bites are to people who step on or very near a coiled snake in dim light, or who are handling one.
Why is the bushmaster declining?
It is a specialist of large, intact, undisturbed lowland rainforest. It hunts by lying in ambush for long periods along the trails of forest rodents, it needs specific microhabitats for its egg clutches, it occurs at naturally low densities, and it reproduces slowly. When forest is logged, fragmented, or converted to farmland, the bushmaster is one of the first snakes to vanish — it does not adapt to disturbed or edge habitat the way the fer-de-lance does. Combined with killing on sight by people who fear it, this has led to it being assessed as Vulnerable, with populations shrinking across much of its range, especially in Brazil's heavily cleared Atlantic Forest.