Legless lizards: Snakes of the Wet Tropics

Skyrail Nature Diary: September 2010

If you are visiting the Wet Tropics, it is common to encounter one or more species of snakes. Though the mention of a snake may make you quiver, these predators play a vital role in assisting with the life cycle in rainforests.

Snakes are reptiles and are closely related to lizards. In fact, lizards are considered to be the ancestors of modern day snakes. Adaptations to the lizard have occurred over time. First the legs disappeared. The reason for this has to do with the snakes' ancestors moving underground. Moving in tight tunnels makes legs not only cumbersome but they also get in the way. To compensate for the loss of limbs, the snakes have lengthened their bodies and modified the scales on their bellies for better grip. External ears were also lost to avoid filling with dirt. While underground, it is easier for the snake to feel for vibrations.

Snake's eyes are covered in a special translucent film, which protects their eyes when digging. Though snakes have very poor eye site, their excellent sense of smell compensates for their loss of site. Partly due to reduced mobility, many snakes developed powerful venoms to incapacitate their victims.

Red-bellied Black Snakes (Pseudechis porphyriacus) are without a doubt the most commonly seen snake in the rainforest (image 1). They often bask in the sun early in the morning before they head off to hunt. Despite the name, the northern race of these snakes have either a yellow or white belly. These snakes are quite flat and broad, with no noticeable neck and are generally quite docile. Despite being venomous, they rarely bite and even then they don't always inject venom. They are an unusual species of snake because they are the only tropical Australian snakes to give birth to live young. It's believed to be an adaptation from a time when the Wet Tropics was located further south in the temperate zone. Eggs were then kept inside the body and kept warm during basking. There is no real advantage of this adaptation.

Taipans and Keelback Snakes (Tropidonophis mairii) are also commonly seen bathing in the rainforest sunlight. Taipans are the second most venomous snakes in the world. They have small hollow fangs and are easily identified. As adults they are one of the larger snakes and usually have a head that is lighter in colour than the rest of the body. They prey on rodents, making them useful for controlling vermin in rainforests.

Keelback Snakes are usually seen near water and are excellent swimmers. They have rear fangs and are mildly venomous. Due to their medium size, they are unable to inject humans. Their diet consists of frogs and fish and are Australia's only snake able to eat cane toadlets without causing any harm to themselves. This makes them extremely valuable in keeping cane toad populations down.

Amethystine Pythons (Morelia amethistina) are Australia's largest snake. In the Barron Gorge National Park (North Queensland, Australia), they grow between three to five metres long (image 2 & 3). They have thick bodies covered in diamond shaped blotches. Unlike most snakes, pythons have two spurs just in front of their tails, which are the remains of their original hind legs.

Pythons kill their victims by constriction. They don't squeeze their prey to death, but rather coil around them as tight as possible. When their prey exhales, they squeeze tighter, eventually killing it.

Like all snakes pythons can loosen their jaws and stretch their bodies around their food, eating their prey whole.