Anacondas are among those animals whose true size is often blurred by legends and movie portrayals. Although there is no reliable evidence of anacondas measuring dozens of metres long, real specimens can still grow to impressive proportions. The largest species, the green anaconda, is considered the heaviest living snake in the world.
The largest anacondas can weigh approximately 227 to 250 kilograms. One reliably recorded, exceptionally large specimen weighed 227 kilograms, measured 8.43 metres long, and had a circumference of 1.11 metres at its thickest point. Most anacondas are considerably smaller, however, and record sizes are reached primarily by adult female green anacondas.
How much does an anaconda weigh?
An anaconda’s weight depends on its species, sex, age, food availability, and habitat. When people refer to an anaconda without specifying the species, they usually mean the green anaconda. This is the species that reaches the greatest weight.
Expert zoological sources put the weight of the largest specimens at approximately 227 to 250 kilograms. The figures differ mainly because some are based on recorded measurements, while others represent the species’ estimated maximum possible size. Exceptionally large anacondas are also rare, and weighing them accurately in the wild is difficult.
The heaviest specimen mentioned by London’s Natural History Museum weighed 227 kilograms. It measured 8.43 metres long and had a circumference of 1.11 metres. Smithsonian’s National Zoo states that the largest green anacondas can reach approximately nine metres in length and weigh around 250 kilograms.
Females are significantly larger than males
Anacondas display one of the most pronounced differences in size between the sexes among snakes. An adult male green anaconda is often about three metres long, while a large female can reach five to six metres. The largest females may weigh several times as much as adult males.
A large body gives females a reproductive advantage. A bigger female can produce more young and has greater energy reserves during the approximately seven-month gestation period, when she may eat very little or nothing at all.
Why can’t an anaconda’s weight be determined from its length alone?
Two anacondas of the same length may not weigh the same. Weight is strongly influenced by body thickness, muscle mass, sex, age, and whether the snake has recently eaten large prey. An anaconda that has swallowed a capybara or another large animal may temporarily be considerably heavier.
Large females have broad, powerful, muscular bodies. This is why an anaconda can be significantly heavier than a longer python. When comparing records, it is therefore important to distinguish between the longest and the heaviest snake.
Is the anaconda the world’s largest snake?
The green anaconda is considered the heaviest living snake in the world. The record for length, however, generally belongs to the reticulated python, which may grow longer but has a more slender body. By comparison, the anaconda is considerably more massive.
It is estimated that an anaconda measuring approximately 5.2 metres may weigh about as much as a reticulated python around 7.3 metres long. The difference is mainly due to the anaconda’s much broader torso, which is adapted for moving through water and hunting robust prey.
The designation “largest snake” therefore depends on what is being compared:
- the heaviest living snake is the green anaconda,
- the longest living snake is generally the reticulated python,
- the largest confirmed anacondas can weigh more than two adults,
- unverified stories of anacondas measuring 15 to 30 metres have no reliable scientific basis.
How long can an anaconda grow?
The largest credibly documented anacondas reach approximately eight to nine metres in length. Reports of longer specimens appear in historical accounts, stories told by local people, and the media, but they often lack a body, an accurate measurement, or any other verifiable evidence.
Measuring large snakes is not easy, even after they have been captured. A live snake writhes, contracts its muscles, and can change its body position. Old skins may also stretch after being removed and processed, so they do not provide a reliable indication of the animal’s original length.
An ordinary adult is therefore not nine metres long. Males tend to be significantly shorter and lighter, while females most commonly measure approximately four to six metres. Specimens approaching eight metres are exceptional.
What is an anaconda?
Anacondas are semi-aquatic snakes of the genus Eunectes, which belongs to the boa family. They live in South America and are close relatives of boas. They are not venomous and kill prey using their powerful, muscular bodies.
The name Eunectes can be translated roughly as “good swimmer.” This describes the anaconda’s way of life far better than its movie portrayal as a lumbering monster moving across land.
The best-known anacondas include:
- green anaconda – Eunectes murinus,
- yellow anaconda – Eunectes notaeus,
- Bolivian anaconda – Eunectes beniensis,
- dark-spotted anaconda – Eunectes deschauenseei.
In 2024, scientists proposed classifying northern populations of the green anaconda as a separate species, Eunectes akayima. However, this taxonomic division remains a subject of scientific debate. The Reptile Database currently provisionally treats the name as a synonym of Eunectes murinus, so the number of recognised species may differ between sources.
Where do anacondas live?
Anacondas occur naturally in tropical and subtropical regions of South America. The green anaconda primarily inhabits the Amazon and Orinoco basins, the flooded Llanos, swamps, slow-moving rivers, lakes, and flooded grasslands.
It is found in countries and territories including Brazil, Venezuela, Colombia, Peru, Ecuador, Bolivia, Guyana, Paraguay, and French Guiana, as well as on the island of Trinidad. The species have different ranges, with some restricted to much smaller areas.
Although anacondas can climb onto riverbanks and smaller individuals may also be found in vegetation, much of their lives is closely associated with water. Their massive bodies are buoyed by the water, allowing them to move more smoothly and stealthily than on solid ground.
Its eyes and nostrils are positioned on top of its head
An anaconda’s eyes and nostrils are positioned high on its head. This allows the snake to remain almost entirely submerged, with only a small part of its face above the surface. Similar adaptations are seen in crocodilians and other animals that hunt in water.
Its olive-green colouring and dark spots provide effective camouflage among aquatic plants, mud, and the shadows of waterside vegetation. As a result, prey may not notice the enormous snake until it attacks.
What do anacondas eat?
The anaconda is a carnivore and an opportunistic predator. Rather than specialising in a single type of prey, it hunts animals it can overpower and swallow. Smaller anacondas feed mainly on fish, amphibians, birds, turtles, and small mammals.
Large adult females can capture considerably bigger prey. Their diet may include:
- capybaras,
- caimans,
- deer and other hoofed animals,
- larger waterbirds,
- turtles,
- fish,
- smaller snakes,
- domestic animals that venture near the water.
Anacondas do not hunt every day. They have slow metabolisms and may spend several weeks digesting a large meal. Substantial prey provides enough energy to sustain them for a long period, during which they do not need to risk hunting again.
How does an anaconda kill its prey?
An anaconda first seizes its prey with its mouth and then wraps one or more coils of its body around it. Its muscles gradually exert powerful pressure that disrupts the prey’s blood circulation. Constrictors were traditionally thought to kill by suffocation, but research on boas has shown that the decisive mechanism may be the rapid restriction of blood flow to the heart and brain.
The snake may also respond to the prey’s heartbeat and adjust the strength of its grip. Once the animal has been immobilised, the snake swallows it whole, usually head first.
An anaconda does not dislocate its jaw
A widespread myth claims that a snake dislocates or detaches its jaw when swallowing large prey. In reality, its jaws do not dislocate. A snake’s skull consists of several movably connected bones, while the two halves of the lower jaw are joined by flexible tissue.
This structure allows the snake to open its mouth widely and gradually move each side over the surface of its prey. Backward-curving teeth help hold the food in place and prevent it from slipping out while being swallowed.
Are anacondas dangerous to humans?
An anaconda is an exceptionally powerful wild snake, so people should not approach one or attempt to catch it. Despite its fearsome reputation, however, attacks on humans are not a normal part of its behaviour. Anacondas generally try to avoid conflict and escape into water or mud when threatened.
A large female could theoretically inflict serious or even fatal injuries on an adult. However, expert zoological sources do not cite any reliably documented cases of a green anaconda killing and then swallowing a person.
This does not mean that anacondas are harmless. They have backward-curving teeth, a powerful grip, and extremely muscular bodies. Danger arises primarily when people handle the snake, try to protect livestock, or put the anaconda in a situation where it feels cornered.
How do anacondas reproduce?
Anacondas do not lay eggs in a nest like many other snakes. The young develop inside eggs within the female’s body and are born live. The gestation period lasts approximately seven months.
During the breeding season, a single female may be surrounded by several males. This creates what is known as a mating ball, which observations suggest may contain as many as 13 males. Mating and competition for access to the female may continue for several weeks.
A female usually gives birth to approximately 20 to 40 young, although considerably larger litters have also been recorded. The largest reported litter contained 82 young. The number of offspring is related to the female’s size and physical condition.
The young may measure approximately 60 to 90 centimetres at birth and are immediately independent. Their mother neither feeds nor protects them after birth. Despite being fairly large, young anacondas may fall prey to caimans, larger birds, wild cats, and other predators.
A female may eat a male
Sexual cannibalism has also been observed in anacondas. After mating, a large female may consume one of the smaller males. This does not happen after every mating, but it may provide the female with energy needed during the demanding gestation period.
The pronounced difference in size between the sexes means that an adult male may be manageable prey for a large female. Females need a long time to recover after reproducing, which is why anacondas often breed only every other year.
How long do anacondas live?
The average lifespan of a green anaconda in the wild is estimated at approximately ten years. Many young individuals do not reach adulthood because they are eaten by predators or die as a result of environmental changes.
Anacondas can live considerably longer in human care. Some individuals have been recorded living for more than 20 to 30 years. In captivity, they are not threatened by natural predators, periods of drought, or a shortage of prey, but they require sufficient space, a suitable temperature, and an aquatic area.
An anaconda is not a suitable pet. It grows quickly, requires specialised care, and an adult can be dangerous even to an experienced keeper. International trade in anacondas and products made from their skins is also regulated.
How does an anaconda locate its prey?
An anaconda does not rely on sight alone. It uses its forked tongue to collect chemical particles from its surroundings and transfers them to the Jacobson’s organ in the roof of its mouth. This allows it to detect the presence of prey or another anaconda.
It is also highly sensitive to vibrations in the ground and water. Heat-sensitive pits along its upper lip help it detect the warmth produced by the bodies of mammals and birds. These abilities are exceptionally useful in murky water and at dusk, when visibility is limited.
Anacondas are usually most active in the late afternoon and evening. They often wait hidden in the water and strike only when prey comes within close range.
Can an anaconda survive the dry season?
Anacondas living near large rivers may remain active throughout the year. Those in seasonally flooded areas, however, must seek out the remaining bodies of water during the dry season.
If they cannot find suitable water, they may burrow into wet mud and greatly reduce their activity. This allows them to conserve energy and protect their bodies from drying out and from high temperatures. Once the rains return and the landscape floods again, they become more active and resume hunting.
The most common myths about anacondas
Anacondas grow to lengths of 20 or 30 metres
No anaconda of this length has been reliably documented. Stories of gigantic snakes may arise from incorrect estimates of distance, stretching of a removed skin, or the gradual exaggeration of an original sighting.
An anaconda can swallow anything
Even a flexible mouth and mobile skull have their limits. The snake must assess whether it can safely kill and swallow its prey. An animal that is too large or dangerous may injure the anaconda, which is why even large individuals often feed on much smaller prey.
Anacondas hunt people
Humans are not normal prey for anacondas. Conflicts are possible, but movies greatly exaggerate the snake’s willingness to pursue people. The anaconda is an ambush predator that prefers prey naturally found in its habitat.
An anaconda crushes all of its prey’s bones
The purpose of constriction is not to crush the skeleton. The pressure primarily restricts the prey’s blood circulation and movement. Fractures may occur, but they are not the main cause of the animal’s rapid immobilisation.
Video: The anaconda, a heavyweight among snakes
Footage from National Geographic shows the green anaconda’s massive build and how it moves through an aquatic environment.
Interesting facts about anacondas
- The green anaconda is the heaviest living snake, but not always the longest.
- Females may weigh several times as much as males.
- Its eyes and nostrils are on top of its head, allowing it to remain submerged.
- It does not use venom, but constricts its prey with its muscular body.
- It swallows prey whole and cannot chew it.
- After a large meal, it may not need to hunt for several weeks.
- It gives birth to live young that are independent from birth.
- A single litter may contain several dozen young.
- It can detect chemical trails with its tongue, as well as vibrations and the body heat of prey.
- It lives for approximately ten years in the wild and may survive for more than 30 years in human care.
- It is considerably more mobile and agile in water than on land.
- During the dry season, it may shelter in mud and reduce its activity.
- Reports of anacondas measuring dozens of metres long have not been scientifically confirmed.
Summary
The largest anacondas can weigh approximately 227 to 250 kilograms and measure more than eight metres long. Record sizes are reached primarily by female green anacondas, which are significantly more massive than males. The anaconda may not be the world’s longest snake, but its broad, muscular body makes it the undisputed record holder by weight.
Despite its cinematic reputation, the anaconda is not a creature that deliberately hunts people. It is a perfectly adapted aquatic predator whose strength, camouflage, senses, and reproductive behaviour make it one of the most remarkable snakes on Earth.
Sources
- Smithsonian’s National Zoo – Green anaconda
https://nationalzoo.si.edu/animals/green-anaconda citeturn737646view0turn737646view1turn737646view2 - Natural History Museum – What is the biggest snake in the world?
https://www.nhm.ac.uk/discover/what-is-the-biggest-snake-in-the-world.html citeturn401123view3 - Animal Diversity Web, University of Michigan – Eunectes murinus
https://animaldiversity.org/accounts/Eunectes_murinus/ citeturn737646view3turn737646view4turn737646view5 - San Diego Zoo Wildlife Alliance – Anaconda
https://animals.sandiegozoo.org/animals/anaconda citeturn401123view2 - The Journal of Experimental Biology – Snake constriction rapidly induces circulatory arrest in rats
https://journals.biologists.com/jeb/article/218/14/2279/14389/Snake-constriction-rapidly-induces-circulatory citeturn271789search0 - Natural History Museum – Snakes: Super senses, stretchy jaws and deadly venom
https://www.nhm.ac.uk/discover/snakes-senses-stretchy-jaws-deadly-venom.html citeturn660523search0 - Diversity – Description of the Northern Green Anaconda: What Is in a Name?
https://www.mdpi.com/1424-2818/16/7/418 citeturn401123view4 - The Reptile Database – Eunectes murinus
https://reptile-database.reptarium.cz/Eunectes/murinus citeturn356452search0
Jana
I like turning curiosity into words, and writing articles is my way of capturing ideas before they slip away — and sharing them with anyone who feels like reading.
