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Forget your favourite nightclub, Friday night in the Amazon is the place to be. It’s the weekly ‘Caiman Cruise’, where I take my student groups out in the canoe to search for caiman by torchlight. My favourite part is looking up in the trees overhanging the river and seeing the golden eye shine of one of my favourite snakes, the Amazon tree boa (Corallus hortulanus). After that it’s just a simple jump from the boat to an overhanging branch and heading up to take a closer look… It’s the only climbing practice I get!

The Amazon tree boa is a slender, arboreal snake, found commonly throughout the Amazon basin. I’ve seen more than I can remember, but I never get tired of them. Juveniles in particular exhibit a wide range of colours and almost every single one I’ve encountered has had a different pattern.

Amazon tree boa (Corallus hortulanus) with ‘flame’ colouration

The boas like to hang out in the trees over the river where they hunt for their main prey source, bats. They have also been reported eating birds, lizards and even primates! They use the infrared sensing heat pits in the labial scales around the mouth to help catch their prey.

Another juvenile with yellow colouration. The infrared heat pits are the indentations visible around the mouth.

Using a scanning electron microscope, some researchers examined the scale micro-ornamentation and compared scales from the dorsal, lateral and ventral (top, side and bottom) of the snake. They also measured the frictional properties of the different parts of the snake. They found that the dorsal and lateral scales have a net like pattern and were similar to each other in their frictional properties.

Large adult boa found in the roof of our dining area

In contrast, the ventral scale micro-ornamentation forms a series of ridges running in the same axis as the length of the snake. When moving forwards, in line with the ridges, the friction is very low, allowing efficient movement through the trees. Amazon tree boas are almost exclusively arboreal, so climbing is an important aspect of their ecology. These snakes can climb vertical branches by wrapping their coils around them, perpendicular to the direction of movement (video at the bottom). This is where the micro-ornamentation comes into its own, causing high friction for upwards movement in this perpendicular position. A good analogy for this is a comb, flowing smoothly through the hair when in line with the ridges going forwards, but difficult to move sideways.

Perhaps I’m missing a trick when climbing up to catch these snakes – next time I’ll coil myself around and slither up…

https://www.youtube.com/watch?v=Z523grPS4L4

Quick facts:

  • Arboreal species found throughout the Amazon basin.

  • Uses infrared sensing heat pits to help catch prey.

  • Scale micro-ornamentation differs between the ventral scales and the dorsal and lateral scales.


Further reading:

  • Berthé, R. A.,Westhoff, G., Bleckmann, H., & Gorb, S. N. (2009). Surface structure and frictional properties of the skin of the Amazon tree boa Corallus hortulanus (Squamata, Boidae). Journal of Comparative Physiology A, 195(3), 311-318.
  • This is the paper is the one looking at the scale micro-ornamentation. They placed pieces of snake on a ramp that slowly raised until the piece started to move. They tested the pieces in different orientations and on different surfaces to obtain friction coefficients. There are also some good photos of the patterns of the ornamentation on the scales.

  • Ribeiro-Júnior,M. A., Ferrari, S. F., Lima, J. R. F., da Silva, C. R., & Lima, J. D.(2016). Predation of a squirrel monkey (Saimiri sciureus) by an Amazon tree boa(Corallus hortulanus): even small boids may be a potential threat to small-bodied platyrrhines. Primates, 57(3), 317-322.
  • This paper describes a case of an adult Amazon tree boa eating a squirrel monkey in Brazil. It has some photos of the monkey it ate which was 95% of the snake’s body weight!







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