Rare. Data on the population abundance of Lachesis muta is scarce in the literature. Furthermore, the likelihood of encountering this species is known to depend on local environmental conditions [8]. For instance, in southern Orinoco River, Venezuela, Barrio-Amorós et al. [14] reported finding only three individuals over three months of sampling. In contrast, within the Turimiquire massif (also in Venezuela), the same sampling effort yielded 12.3 individuals, indicating a higher density than in the Atlantic Forest, where only one individual was reported per 32.5 hours of search effort [8]. Conversely, an 18-month snake inventory in northern Bahia, Brazil, failed to detect any individuals in the field, with a single specimen recorded only from museum collections [15].
Although rigorous population studies are still lacking, these reports suggest that L. muta can be sighted with relative frequency in some primary forests, while in other parts of its range, it is considered rare. Consequently, the species is generally regarded as uncommon across its overall distribution [8]. A significant knowledge gap exists regarding the natural history of L. muta in Colombia, as it has not been the subject of any local scientific research.
Lachesis muta is a nocturnal, terrestrial species that primarily inhabits forest floors with abundant leaf litter. It can also be found, though less frequently, in secondary forests or adjacent open areas [8,9]. There are also documented reports of this species within cocoa plantations [15]. During the day L. muta individuals are typically in a torpor state, even though during the breeding season the males adopt an aggressive attitude and remain in a combative posture with each other, even during daylight hours. Individuals of this species often stay under fallen trees or in burrows built by mammals, mainly agoutis (Dasyprocta spp.), pacas (Agouti paca), spiny rats (Proechimys spp.), and armadillos of the genera Dasypus y Priodontes, or in rocky cavities [9].
This snake mainly feeds small and medium-sized mammals that are usually between 200-525 g [16], including rodents (rats, mice, spiny rats, squirrels, porcupines) and marsupials, of the taxa Akodon, Oryzomys, Proechimys, Sciurus, Coendu melanurus y Monodelphis brevicaudata [9]. To capture their prey, they employ ambush as a strategy (sit-and-wait), while this is a species that can be considered very active compared to other pitvipers such as Bothrops species, and Crotalus durissus, and that feeds frequently due to the relatively small size of their prey [16].
Lachesis muta is an oviparous species and represents the only confirmed clade of New World pitvipers to exhibit both egg-laying and parental care [9,21]. The average clutch size is estimated to be 6-11 eggs [9], though considerable variation exists. Records from captive breeding report clutches of 6 to 20 eggs [10,16,22, 23], while data from wild specimens indicate a range of 3 to 14 eggs [20]. Currently, no positive correlation between female body size and clutch size or egg dimensions has been demonstrated.
The four nominal species of Lachesis have similar gestation and incubation periods. Reported values (in days) are L. acrochorda: gestation (g)= 110, incubation (i)= 93 [24]; L. stenophrys: g= 100-115, i= 60-90 [9,25–28]; L. melanocephala: g= 101, i= 66-75 [26]; L. muta: g= 70-100, i= 60-79 [9,10,17,22, 23]. It is critical to note that these data originate from captive individuals, where varying incubation protocols involving temperature and moisture—factors fundamental to embryonic development—can significantly affect incubation duration [21]. Combining gestation and incubation, females may spend up to seven months without feeding.
The reproductive phenology of L. muta appears to vary geographically. Some sources propose an absence of distinct seasonal reproduction, citing records of eggs, neonates, and gravid females throughout the year without a clear modal pattern [17,18]. These sources also suggest that sexual activity is stimulated by cold fronts and storms [17,18]. In contrast, studies of Brazilian populations in the Atlantic and Amazon Forests demonstrate marked seasonality, with copulations occurring from April to September—the driest and coldest season in the Amazon—and oviposition from November to February. Neonate emergence then takes place between January and April, coinciding with the onset of the rainy season [19,20].
This apparent contradiction reflects the limited consolidated knowledge of its reproductive biology. Furthermore, truly a seasonal reproduction is rare in tropical snakes [40], suggesting that the reported continuous reproduction in this species is likely an artifact of insufficient data rather than a genuinely atypical reproductive strategy.
Neonates measure 40–54.2 cm in total length. Males reach sexual maturity at approximately 122–129 cm in total length, while females mature at about 112–164 cm, typically within 1–2 years. Under human care, individuals have been known to live for up to 16 years and potentially longer [41]
Given its wide distribution, it is likely that L. muta employs different reproductive strategies in response to local environmental conditions. This plasticity may be facilitated by the female's ability to store sperm, allowing for fertilization at the most suitable time for offspring survival [19], although this hypothesis has not yet been formally assessed.
