Eunectes notaeus
yellow anaconda

Yellow anacondas occur in southern South America, including Paraguay, southern Brazil, northeastern Argentina, and Bolivia. (Burton, 1967)

Yellow anacondas can be found in swamps and marshlands with slow-moving rivers or streams. They can also be observed in forests searching for large game, such as brocket deer or peccaries. During droughts they can be found using caves for shelter and along river banks in holes that retain water. During the rainy months, yellow anacondas can be found in flooded, treeless areas, where they hunt for aquatic species such as fish or caimans (Caiman). (Burton, 1967)

Although yellow anacondas are much smaller than green anacondas (Eunectes murinus, the world's largest snakes) they do reach lengths of up to 4.6 meters (typical adult range 3 to 4 m). Yellow anacondas have yellowish-green scales with brown or blackish bands and overlapping spots that wrap around the entire body. This provides camouflage in murky water or in forest vegetation. Females grow longer than males and generally weigh more as well. Male yellow anacondas can reach up to 3.7 m in length while a female can reach a length of 4.6 m. (Mattison, 1986; Owen, 2004)

Females, after a 6 month gestation period, give birth to fully-developed live young. These young are immediately able to live on their own. Yellow anacondas seem to have indeterminate growth. (Leen, 1978)

Most mortality in yellow anacondas occurs as young, when they are smaller and vulnerable to predation. Once they reach adult sizes, yellow anacondas have few natural predators. The typical lifespan for yellow anacondas in the wild is from 15 to 20 years. In captivity yellow anacondas can live up to 23 years. Humans greatly influence the lifespan of yellow anacondas in the wild, as poaching has decreased the number of yellow anacondas to a dangerously unstable level. (Leen, 1978; Simon, 1992)

Yellow anacondas are strictly solitary, found only with other yellow anacondas for mating. Yellow anacondas may spend up to several months in courtship and mating, but separate once mating is complete. Most of their time is spent in aquatic habitats, hunting prey, although they venture onto land for mating, moving to other water bodies, or hunting occasional terrestrial prey. In times of drought yellow anacondas actively seek swamps and marshes with enough water in which to hunt. They are considered timid snakes and normally try to escape from predators, such as humans, but they will defend themselves when threatened. (Crompton, 1893; Leen, 1978)

Home Range

No information is available on home range size. Yellow anacondas do not seem to defend territories. (Simon, 1992)

Yellow anacondas are solitary animals, except in breeding season. Females attract mates through pheromones. Male anacondas will follow this pheromone trail and, once the potential mates encounter one another, they communicate by rubbing one another and proceed with courtship. All anacondas (Eunectes) have heat-sensing pits located along their mouths. These pits are used to find prey by detecting body heat given off by warm blooded animals. Like most snakes, yellow anacondas do not hear well, although they can pick up vibrations through their jaws. Yellow anacondas, like most snakes, rely heavily on their fork-like tongues and chemosensation to navigate their environment and help find prey. The tongue is flicked in and out of the mouth to taste the air, chemicals collected by the tip of the tongue are deposited in the vomeronasal organ on the top of the mouth. (Mattison, 2007)

Yellow anacondas are generalist carnivorous, preying mainly on animals found in wetland and riparian areas throughout their range. Their diet consists of birds, bird eggs, small mammals, turtles, lizards, occasional fish or fish carrion, and caimans. Wading birds may be their most common prey in some areas. They can reach sizes sufficient to take larger prey, such as brocket deer, peccaries, or capybaras. Yellow anacondas are considered ambush hunters and constrictors. They lay in wait in the water or in vegetation and strike at prey that pass. When prey are grabbed, they begin to wrap their body around the prey and begin constriction. With each exhalation of the prey, the constrictor can squeeze tighter, eventually causing asphyxiation. They may also pull the prey under water during constriction. Yellow anacondas then swallow prey head first by unhinging their jaws, as do other snakes. Along with their incredible jaw flexibility, yellow anacondas have more than a 100 recurved teeth that help to hold and swallow prey. Their digestive system is relatively slow and yellow anacondas may eat only every few days or months, depending on the size of their last prey item. Like other snakes, yellow anacondas can survive long periods without prey. In the wild most predation occurs from June to November, during the relatively dry periods when wetlands areas have shrunk. (Linley, 1993; Parker, 1963; Strussmann, 1997)

Adult yellow anacondas have no natural predators. Humans are their main predators and they are hunted for their skin, for the zoo and pet trade, persecuted out of fear, and their habitats are destroyed. Predators of juvenile yellow anacondas include crab-eating foxes (Cerdocyon thous), tegu lizards (Tupinambis merianae), caimans (Caiman crocodilus), and larger anacondas (Eunectes). In order to avoid predation, young anacondas are camouflaged, as their dark-spotted patterns hides them in the vegetation. ("Anaconda", 1971; Parker, 1963)

Adult yellow anacondas are keystone species; they are one of the top predators in the ecosystems they inhabit. Yellow anacondas influence the number of prey animals, which influences the populations of other prey animals and predators. Ticks from the family Ixodidae are found on yellow anacondas. However, yellow anacondas produce an odor that deters ticks from attaching themselves. ("Anaconda", 1971)

Yellow anacondas are large and aggressive snakes that can inflict damage on humans if approached or threatened. They may even pose a predation risk to small children, but attacks on humans by yellow anacondas are exceptionally rare. ("Anaconda", 1971)

Yellow anacondas are hunted for their skin to make merchandise such as purses, shoes, and belts. Yellow anacondas are also taken for the pet trade. However, anacondas are unpredictable and dangerous and few people take on the challenge of keeping an anaconda as a pet. Yellow anacondas are kept by zoos, where they are a popular attraction. People are intrigued by these species and also terrified by them. ("Anaconda", 1971)

Yellow anacondas are on the IUCN Red List as threatened due to poaching. It is illegal to hunt yellow anacondas in most of South America. This law has helped population numbers to increase, but pet trading and zoos still threaten their survival. ("Anaconda", 1971)