... ...

Episode 296: Gigantic Green Anaconda

Listen on Apple Podcasts


The Green Anaconda (image from www.houstonzoo.org)

Slithering through the jungles of South America is the heaviest snake in the world, the green anaconda, with historical records reporting individuals as large as 9 metres, although this has never been officially proved. The largest proven snake ever found in the wild was 5.21 metres and weighed 97.5 kilograms, unearthed by Dr Jesus Antonio Rivas, a world leading anaconda scientist who has observed over a thousand of the snakes. In captivity, this record was beaten by a female anaconda in Pittsburgh Zoo, who reached the grand old size of 6.27 metres. Currently, there is a $50,000 reward for anyone who can catch an anaconda larger than this size, but thanks to the remote locations these snakes reside in and the difficulty in transporting a snake for confirmation has made this particularly challenging for any aspiring snake hunters out there.

Semi-aquatic, anacondas can be found throughout the swamps and slow-moving streams of the Amazon and the Orinoco River basins, and at least one individual has been found in the Florida Everglades, suggesting these snakes are becoming invasive in the United States. They are specially adapted with their eyes positioned on the top of their head, enabling them to keep an eye out for prey whilst keeping submerged out of sight.

Lifestyles of the Amazon Giants

Green Anacondas are primarily nocturnal and spend most of their lives in or around water. They will eat virtually anything they can overpower, and constrict the prey between their powerful muscles, crushing them to death. The largest snakes can take down prey as large as capybara, tapirs and caimans, although this can be risky for the snake, resulting in injury or even in extreme cases, death. One meal will keep an anaconda going for several months thanks to their extremely low metabolism. Although there are many legends that paint the green anaconda as a man-eater, there is little to no evidence to prove this, although some field researchers have reported being attacked whilst on surveys in the depths of the jungle. However, there are many reports of anacondas cannibalizing their own, usually a female attacking and eating a male. No one knows exactly why they do this, but some researchers have suggested that as females require extra nutrition for making their eggs, the male just unfortunately makes for a handy snack.

Shrinking green: the plight of the Amazon rainforest

The amazon basin as seen from a satellite image (image from fineartamerica.com). The basin is over 7 million square kilometres and is the largest river drainage in the world. The green anaconda, as well as a multitude of other species, call these freshwaters and jungles home.

Although the Green Anaconda is listed as Least Concern on the IUCN red list, its rainforest home is under enormous pressure. Currently, the level of Amazon deforestation is estimated at 17%, which brings the rainforest dangerously close to its tipping point of 20-25%. This is classed as the point at which the Amazon will not generate its own rainfall and support its own ecosystems. High levels of illegal logging and gold mining, unchecked agricultural expansion and a lack of effective law enforcement are pushing the Amazon to its limit. Of particular relevance for the Anaconda, the river basins of the Amazon and their freshwater ecosystems are under threat and often their conservation is neglected. Dam building, mining and land use change are all affecting the Amazon basins hydrological connectivity; the movement of water throughout the rainforest and the nutrients it carries. Dams can alter the position and timing of floodplains and land use change, which is most often due to the conversion of prime habitat into vast agricultural monocultures, can change the amount of water that drains into rivers and is taken up by plants. This affects not only the species that rely on the Amazon rivers and their basins, like the Anaconda, but the rainforest ecosystem as whole. Temperatures of rivers and streams can change as the flow of the Amazon rivers are redirected around dams and other blockages. Many indigenous people rely on the waters of the Amazon for their survival and livelihoods, fishing the vast diversity of aquatic life and using the waterways to trade between villages. Much of the policy regarding the management of rivers around the Amazon simply isn’t strong or consistent enough to tackle the damage being done. In order to be effective, policies have to be applied to the whole river basin and enforced strongly.

Conservation optimism

Although the situation in the Amazon is dire, the importance of conserving this giant rainforest has long been understood, and many heavy hitters, like the WWF, have had long standing conservation plans in place. Many charities are solely focused on the mammoth task of protecting the Amazon, such as Amazon Conservation.

This conservation charity was founded in 1999 by two local conservationists, initially supporting Brazil Nut farmers to grow their business sustainably, whilst protecting the ecosystem they were so reliant upon. They believe in pragmatic conservation, enabling locals to run successful businesses without costing the rainforest. They have three stations throughout the Amazon, where they conduct vital research that drives their conservation interventions.

You can see the fruits of their labor at www.amazonconservation.org/what-we-do/our-results/and learn more about how they conserve both the ecosystem and the lives of the people that rely on it.

To take action alongside Amazon Conservation, you can donate to fund their essential work on their website at https://live-amazon-conservation.pantheonsite.io/take-action/donate, spread the word on social media (check out @AmazonConservation on Instagram), research or volunteer through their field stations, and if you fancy a once in a lifetime holiday, you can even arrange a visit to see their action in person, with all money spent going straight back into their conservation operations.

The WWF have a specialized freshwater conservation plan in place for the development of dams, which you can check out at https://www.wwf.org.uk/what-we-do/projects/finding-balance-between-hydropower-and-nature.

Awesome videos!


Castello, L. (2021) ‘Science for conserving Amazon freshwater ecosystems.’ Aquatic Conservation.

Castello and Maced. (2015) ‘Large scale degradation of Amazonian freshwater ecosystems.’ Global Change Biology.


Rivas, J.A. (1998) ‘Predatory attacks of green anacondas on adult human beings.’ Herpetological Natural History.

Rivas, J.A. (2000) ‘The life history of the Green Anaconda with emphasis on its reproductive biology.’ PhD thesis, University of Tennessee.




September 14, 2022
Scroll to top