Reports of giant anacondas date back as far as the European colonization of South America, when sightings of giant anacondas began to circulate amongst colonists. The size of the largest anacondas has been the subject of debate ever since among cryptozoologists and zoologists.
Anacondas have been verified to grow to sizes of 5.5 metres (18.0 ft), and 100 kilograms (220.5 lb). In particular, the green or common anaconda is the heaviest and largest among all extant snakes in terms of robustness, and it is also the second-longest.
While the longest reputably-measured and confirmed anaconda was about 5.5 metres (18.0 ft) long, extreme lengths far in excess of this have been reported for this species, without verification. Some claims describe anacondas ranging from 8 metres (26.2 ft) to 12 metres (39.4 ft), although these remain unverified.
The first recorded sightings of giant anacondas were from the time of the colonization of South America, when early European explorers entered the dense jungles and claimed to have seen giant snakes measuring up to 18 metres (59.1 ft) long. Natives also reported seeing anacondas upwards of 10 metres (32.8 ft) to 18 metres (59.1 ft). Anacondas above 5 metres (16.4 ft) in length are rare. The Wildlife Conservation Society has, since the early 20th century, offered a large cash reward for live delivery of any snake of 30 feet (9.1 m) 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 17 feet (5.2 m) 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 (37.4 ft) in length, but its claim has never been proven.
Scientist Vincent Roth claimed to have shot and killed a 10.3 metres (33.8 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 (62.3 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. Historian Mike Dash writes of claims of even larger anacondas, alleged to be as long as 45 metres (147.6 ft), with some of the sightings supported with photos (although the photos lack scale). Dash noted if reports of a 18 metres (59.1 ft) anaconda strains credulity, then a 120 feet (36.6 m) long specimen would be an impossibility.
Anacondas have been featured in many stories around Latin America, such as those written by Uruguayan writer Horacio Quiroga, who also founded group of Argentine and Uruguayan intellectuals around 1920 called the Anaconda Association. He also published a book named Anaconda around 1921. Willard Price, famous author of many children's books in the early 1900's, wrote about a 10 meter Anaconda in "Amazon Adventure".
An anaconda was featured in an episode of Lost Tapes called "Megaconda".
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