Anacondas are among the heaviest snakes on Earth, lurking in the rivers and swamps of South America where their weight is no burden at all. Despite their fearsome reputation, most of what people "know" about anacondas is exaggerated movie myth.
Here are the real, verified facts about these massive constrictors, from their true top size to a genuinely strange reproductive trick some females can pull off.
The green anaconda (Eunectes murinus) is the heaviest snake in the world; large females can weigh 300-500+ pounds, with the biggest confirmed individuals near 550 pounds.
Most green anacondas measure well under 20 feet; claims of individuals up to 29-30 feet exist in extreme, less-rigorously-verified reports, but a scientifically confirmed specimen ("Ana Julia") measured about 20.7 feet and weighed 441 pounds.
Anacondas live in the rainforests, rivers, and swamps of tropical South America, including the Amazon and Orinoco basins.
Anacondas are not venomous. They kill prey by constriction, tightening their coils each time the prey exhales until it can no longer breathe.
They are ambush predators that spend much of their time submerged, with their eyes and nostrils positioned on top of the head so they can watch and breathe while almost entirely underwater.
Anacondas are strong swimmers and can hold their breath and stay submerged for around 10 minutes at a time.
Adult anacondas have very few natural predators aside from jaguars and caimans on rare occasions; humans (through hunting and habitat loss) are their main threat.
Female anacondas are significantly larger than males, a trait known as sexual size dimorphism that is unusually pronounced in this species.
Anacondas are cold-blooded (ectothermic), relying on their environment rather than internal metabolism to regulate body temperature.
They are most active in the evening and at night, spending much of the day resting in water or along the banks.
Anacondas have a somewhat prehensile tail that helps them anchor themselves while resting partly submerged or along the water's edge.
Their teeth are small, sharp, and curved backward, ideal for gripping struggling prey rather than chewing it.
Anacondas can go weeks between meals thanks to a slow metabolism, and very large individuals can sometimes go months without eating after a big meal.
They prey on fish, birds, capybaras, deer, and occasionally caimans, using their bulk and strength to overpower animals larger than many other predators would attempt.
Wild anacondas typically live around 10 years, though captive individuals have lived considerably longer, sometimes past 20-30 years, under managed care.
Anacondas are largely solitary and typically only come together during the breeding season, when multiple males may compete for a single female in a "breeding ball."
Anacondas have remarkably flexible jaws connected by stretchy ligaments, letting them swallow prey much wider than their own head.
In 2017, DNA analysis confirmed a green anaconda at a Japanese zoo gave birth via facultative parthenogenesis, producing offspring with no father after years of isolation from males, a genuine rare case of asexual reproduction in this species.
Their olive-green bodies are marked with large black blotches, camouflage that works especially well in murky water and dappled riverbank light.
As apex predators in their ecosystem, anacondas help keep populations of fish, birds, and other prey animals in check.
Anacondas are not aggressive toward humans by nature and typically only strike if cornered, threatened, or accidentally provoked.
Female anacondas give birth to live young, typically producing 20 to 40 babies per litter after retaining fertilized eggs internally for several months.
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