Bolivian Anaconda (Eunectes beniensis)

Bolivian Anaconda

Eunectes beniensis, commonly known as the Bolivian anaconda or Beni anaconda, is a species of non-venomous, aquatic snake in the boa family (Boidae). It is endemic to the Beni wetlands in northern Bolivia and was only formally recognized as a distinct species in 2002. Closely related to the green anaconda (Eunectes murinus), the Bolivian anaconda occupies a narrow transitional zone within the Amazon Basin and exhibits physical traits that are intermediate between the green and yellow anacondas.

Taxonomy and Classification

The genus Eunectes includes the four known species of anacondas:

Eunectes murinus (green anaconda)

Eunectes notaeus (yellow anaconda)

Eunectes deschauenseei (dark-spotted anaconda)

Eunectes beniensis (Bolivian anaconda)

The Bolivian anaconda was long thought to be a regional population or a possible hybrid of green and yellow anacondas. However, a study published in 2002 based on morphological and genetic data provided strong evidence that E. beniensis is a distinct species. It occupies a unique geographic and ecological niche, and its genetic makeup confirms its separation from the other three species.

Description

The Bolivian anaconda is a large, muscular snake that closely resembles the green anaconda in overall body shape and size, but with subtle differences in coloration and patterning. Adults can reach lengths of 3.5 to 4.5 meters (11.5 to 15 feet), though some individuals may exceed this range. While not quite as massive as the largest green anacondas, they are still among the heaviest snakes in the world.

Coloration and Pattern

The coloration of the Bolivian anaconda is considered to be intermediate between the green anaconda (E. murinus) and the yellow anaconda (E. notaeus). Its dorsal surface is generally olive green or dark brown, with large dark blotches or spots along the body. These markings are more distinct than those of the green anaconda but less vivid than the bold black patterns of the yellow anaconda. Its ventral surface is pale, often with scattered dark markings. The head is relatively large and broad, with distinctive stripes that extend from the eyes toward the jawline.

Distribution and Habitat

Eunectes beniensis is endemic to the Beni wetlands, a vast and seasonally flooded region of northern Bolivia that lies within the southwestern portion of the Amazon Basin. The Beni wetlands, also known as the Llanos de Moxos, are characterized by a mosaic of rivers, floodplains, lakes, savannas, and forests. This region is extremely biodiverse and supports a wide variety of aquatic and semi-aquatic species.

The Bolivian anaconda is particularly associated with slow-moving rivers, oxbow lakes, swamps, and marshes. It is highly aquatic, spending the majority of its time in water. During the rainy season, when the wetlands expand dramatically, the snakes may disperse over a wide area. In the dry season, they often retreat to more permanent water bodies.

Behavior and Ecology
Aquatic Lifestyle

Like other anacondas, E. beniensis is a powerful swimmer and is well-adapted to life in water. Its eyes and nostrils are located on the top of its head, allowing it to remain almost entirely submerged while stalking prey or avoiding detection. On land, it is more sluggish and vulnerable, preferring to stay close to water at all times.
Diet

The Bolivian anaconda is a non-venomous constrictor that feeds on a variety of vertebrate prey. Its diet includes:

Fish

Amphibians

Birds

Reptiles

Mammals (such as capybaras and small deer)

Anacondas kill by wrapping their muscular bodies around the prey and constricting until suffocation occurs. They then swallow the prey whole, aided by their flexible jaws.

Juvenile anacondas tend to feed on smaller prey like frogs, fish, and aquatic rodents, while adults are capable of taking down much larger animals. The ability to remain hidden in murky water makes them effective ambush predators.

Reproduction

Bolivian anacondas are ovoviviparous, meaning they give birth to live young rather than laying eggs. Mating typically occurs during the dry season when snakes are concentrated around dwindling water sources. Males may engage in "breeding balls," where multiple males coil around a single female in competition for mating rights.

Females have a long gestation period that may last up to 6–7 months. Litters can range from 10 to over 40 neonates, depending on the size and health of the mother. Newborns are typically around 60–70 cm in length and are independent from birth.

Conservation Status

As of now, the International Union for Conservation of Nature (IUCN) has not separately evaluated the conservation status of Eunectes beniensis. Due to its recent classification and limited distribution, there is relatively little known about its population numbers or long-term threats. However, the Beni wetlands are under increasing pressure from human activity, including agriculture, cattle ranching, and infrastructure development.

Habitat degradation, pollution, and climate change pose potential threats to the species. Furthermore, like other large snakes, Bolivian anacondas may be persecuted out of fear or killed for their skin.

Human Interactions

Because the Bolivian anaconda lives in relatively remote wetlands, it has limited direct contact with humans. Nonetheless, as human settlement expands and tourism in the region increases, sightings of the species are becoming more common. These snakes are not considered dangerous to humans, though their large size and strength mean that caution is always advised when encountered in the wild.

Cultural attitudes toward anacondas vary widely, with some local communities viewing them with superstition or fear, while others respect them as important members of the ecosystem. In Bolivia, efforts are being made to preserve the ecological integrity of the Beni wetlands, which would also benefit E. beniensis and other endemic species.

Discovery and Recognition

The Bolivian anaconda was first distinguished as a potentially unique population in the 1990s, but it was not until a detailed study by researchers Jesus Rivas, Gordon Schargel, and others in 2002 that the species was formally described. The research included both morphological comparisons and genetic analyses, which showed that E. beniensis is genetically distinct from both E. murinus and E. notaeus. This discovery contributed to a better understanding of anaconda diversity and the biogeography of South American snakes.

Fun Fact

Despite its large size and imposing appearance, the Bolivian anaconda remained hidden from science for centuries. It wasn’t until the 21st century that it earned its rightful place as the fourth recognized species of anaconda. This is a testament to how much of the natural world remains unexplored, even in relatively well-known regions like the Amazon.

See Also

Eunectes murinus (Green anaconda)

Eunectes notaeus (Yellow anaconda)

Amazon rainforest

Beni wetlands

Constriction (zoology)