Reports of giant anacondas date back as far as the discovery of South America, when sightings of anacondas upwards of 50 metres (164 feet) began to circulate amongst colonists, and the topic has been a subject of debate ever since among cryptozoologists and zoologists. Anacondas can grow to sizes of 6 metres (20 ft) and beyond, and 150 kilograms (330 lbs.) in weight. Although some python species can grow longer, the anaconda, particularly the green or common anaconda, is the heaviest and largest in terms of diameter of all snakes, and it is the second-longest extant snake in the world behind the reticulated python. The longest reputably-measured and confirmed anacondas are about 7.5 metres (25 feet) long. Lengths of 50–60 feet have been reported for this species, but such extremes lack verification. The only real reliable claims that can be found describe measured anacondas ranging from 26 to 39 feet, although these remain unverified.
The first recorded sightings of giant anacondas were from the time of the discovery of South America, when early European explorers entered the dense jungles and claimed to have seen giant snakes measuring up to 18 metres (59 ft) long. Natives also reported seeing anacondas upwards of 10.5 metres (34 ft) to 18 metres (59 ft). Anacondas above 7 metres (23 ft) in length are rare. The Wildlife Conservation Society has since the early 20th century, offered a large cash reward (currently US$50,000) for live delivery of any snake of 9 metres (30 ft) or more in length, but the prize has never been claimed, despite the numerous sightings of giant anacondas. In a survey of 780 wild anacondas in Venezuela, the largest captured was 5 metres (16 ft) long. A specimen measured in 1944 exceeded this size when a petroleum expedition in Colombia claimed to have measured an anaconda which was 11.4 metres (37 ft) in length, but its claim has never been proven.
Scientist Vincent Roth claimed to have shot and killed a 10.3 metres (34 ft) specimen, but like most other claims, it lacks sound evidence. Another claim of a large anaconda was made by British adventurer Percy Fawcett. Following his 1906 survey of the Bolivia/Brazil border, Fawcett wrote that he had shot an anaconda that measured some 19 metres (62 ft) from nose to tail. Once published, Fawcett’s account was ridiculed. Decades later, Belgian cryptozoologist Bernard Heuvelmans came to Fawcett's defence, arguing that Fawcett's writing was generally honest and reliable. In Fawcett's favour is the fact that he was conducting a field survey and would have had at his disposal suitable measuring instruments. In an earlier part of his diary, he suspects a claim that an anaconda of 17.67 m. (58 ft.) was discovered was "exaggerated" until his own discovery of the larger snake.
Historian Mike Dash writes of claims of even larger anacondas, alleged to be as long as 45 metres (148 ft), with some of the sightings supported with photos (although the photos lack scale). Dash noted if reports of a 18 metres (59 ft) anaconda strains credulity, then a 120 feet (37 m) long specimen would be an impossibility.
Perhaps the most well-known film portrayal of a giant anaconda in popular fiction is the 1997 film Anaconda, which featured a giant anaconda hunting and killing several crew members from National Geographic, and its sequel Anacondas: The Hunt for the Blood Orchid. Another two sequels, Anaconda 3: Offspring and Anacondas: Trail of Blood, were produced as made-for-television films in 2008.
It was featured in an episode of Lost Tapes called "Megaconda".
On the episode "Amazon Assassins" of River Monsters, Jeremy Wade was trying to find and catch a large Arapaima when locals told him about the "Cobra Grande", a giant snake different from the anaconda. The witnesses took him to the spot where they first found the snake, apparently basking. The witnesses claim to have shot the snake three times and that they later found three lumps of lead on the spot where the snake was basking. The witnesses showed Wade a large burrow which they claim the snake escaped into after they shot at it. While he did not find the snake itself, the entrance to the burrow was littered with shed snakeskin.
During an expedition in the Peruvian Amazon in 2009, a Belfast father and his son claim to have captured a giant anaconda on camera. One interpretation of the photograph claims the "snake" has tentacles; as a result one alternative explanation is that it is an unknown species of giant caecilian, see Minhocão.
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