Anacondas belong to the genus Eunectes, a group of large, non-venomous boa species native to the tropical river systems and wetlands of South America. The name Eunectes comes from ancient Greek, translating roughly to “good swimmer,” highlighting their highly aquatic lifestyle. These snakes are renowned for their size, making them some of the largest reptiles on Earth. Traditionally, four species of anacondas have been recognized, distinguished by their size, coloration, and geographical distribution.
The Green Anaconda
The Green Anaconda, Eunectes murinus, is the most famous member of the genus and holds the title of the world’s heaviest snake. Adult females are much larger than males, typically reaching 4.6 meters (15 feet) and weighing between 30 to 80 kilograms (66 to 176 pounds). This species is considered the largest snake by weight and circumference. Their coloration is an olive-green base with large, dark, circular blotches running along the body, providing excellent camouflage in murky water.
These apex predators are found primarily in the Amazon and Orinoco river basins, thriving in the slow-moving rivers, swamps, and seasonally flooded grasslands, or llanos. Their eyes and nostrils are positioned on the top of their heads, allowing them to remain almost completely submerged while waiting in ambush for prey. The diet of the Green Anaconda is varied and opportunistic, including fish, birds, capybaras, caimans, and even large mammals like deer and tapirs, which they kill by constriction.
Reproduction involves a “breeding ball,” where a single female is courted by multiple smaller males for several weeks. Females are ovoviviparous, retaining eggs internally and giving birth to live young after a gestation period of six to seven months. A single female can produce a large litter, averaging 20 to 40 offspring, which are born already capable of swimming and hunting.
The Yellow and Dark-Spotted Anacondas
The Yellow Anaconda, Eunectes notaeus, is a large constrictor, with adults typically growing to an average of 3.7 meters (12 feet). They are characterized by a yellowish, golden-tan, or greenish-yellow background color overlaid with black or dark brown blotches and streaks. This species occupies a southern range, primarily inhabiting the Parana and Paraguay river basins, including the Pantanal wetlands and parts of Argentina, Paraguay, and Bolivia.
Like all anacondas, the Yellow Anaconda is highly aquatic, preferring swamps, marshes, and the brush-covered banks of slow-moving streams. Their reproductive habits are similar to the Green Anaconda, with the female giving birth to live young, though their litters are typically smaller. Their smaller size also results in a proportionally smaller prey base, consisting mainly of birds, small mammals, and aquatic animals.
The Dark-spotted Anaconda, Eunectes deschauenseei, reaches a maximum length of about three meters. Its distribution is restricted to the northeastern coastal regions of South America, specifically coastal French Guiana and northern Brazil. This snake is named for its unique and prominent dark spotting pattern against a drab background.
This species is closely related to the Yellow Anaconda, and its taxonomic status has been a subject of debate. It inhabits the seasonally flooded wetlands and swamps of its limited range. Due to its rarity, specific details about its diet and reproductive cycle in the wild are not as well documented as the other species.
Defining the Fourth Species and Taxonomic Updates
The four historically recognized species included the Green, Yellow, Dark-spotted, and Bolivian Anacondas (E. beniensis). The Bolivian Anaconda, restricted to the Beni region, can reach up to four meters in length. It was initially thought to be a hybrid between the Yellow and Green anacondas before being recognized as a distinct species in 2002.
The understanding of the genus Eunectes is not fixed, and recent scientific discoveries have complicated the classic “four types” classification. A major genetic study published in 2024 revealed that the traditional Green Anaconda is actually two genetically distinct species. The newly identified species, named the Northern Green Anaconda (Eunectes akayima), inhabits the northern parts of the range, including the Orinoco basin.
This discovery means the Southern Green Anaconda retains the name Eunectes murinus, while the northern population is now E. akayima. The same research proposed unifying the Bolivian and Dark-spotted Anacondas with the Yellow Anaconda, suggesting they are variations of a single species. While people commonly cite four types, modern taxonomy now recognizes a minimum of five anaconda species, with E. akayima being the most recent addition to the genus.