Live birth is the rule among pit vipers, and rattlesnakes, lanceheads and copperheads all deliver fully formed young. Lachesis is the exception in the Americas: females deposit a clutch of roughly a dozen eggs, often in an abandoned burrow or under forest debris, and remain coiled around them through incubation.
The species is also the largest viper anywhere, with credible records above three metres and exceptional individuals reported longer. Size does not translate to encounters. Bushmasters occur at low density, require large tracts of undisturbed forest, hunt at night and spend long periods motionless, so bites are rare even where the snake is present.
That dependence on intact forest is why the species is assessed as at risk while many of its relatives are not. Estimates of population size are weak, since standard survey methods find very few animals, and much of what is claimed about bushmaster behaviour rests on captive observation rather than field study.