Cold-blooded Snakes

02 October, 2011

White-lipped Snake, <i>Drysdalia coronoides</i>
White-lipped Snake, Drysdalia coronoides
Image: Peter Robertson
Source: Wildlife Profiles Pty Ltd

Question: Are snakes really cold blooded? Are you more likely to see them on hot or cold days?

Answer: Snakes are commonly referred to as cold blooded, but this term is misleading.

Snakes are Ectothermic. This means that their body temperature is determined by the temperature of their surroundings.

However, snakes do have control over their body temperatures; they can move in and out of the sun, or retreat into the shade or underground. This is called thermoregulation. A snake's body temperature can therefore be quite different from the ambient air temperature. For example, a dark-coloured snake lying in the sun on a cool day will be much warmer than the air temperature.

As a very general rule, snakes like to have a body temperature of between 20 and 35˚c. When their body temperatures drop below 20˚c, they will try and find somewhere warmer; when their body temperatures are getting close to 35˚c, they will seek a cooler retreat sites.

Snakes are much more able to tolerate cold temperatures than hot temperatures. If a snake gets too hot, it can suffer tissue and brain damage. It is therefore crucial that snakes have access to cool retreat sites in hot weather.

When it gets cold, their metabolism and movement slows down. This is not a problem if they are in a safe retreat site, but a slow-moving snake could be in great danger if a predator came along. In winter, when there are few opportunities to warm up and less food available, many snakes simply hunker down and remain inactive until spring.

You're therefore most likely to see a snake when it's cool enough that snakes want to warm up. At these times, snakes will seek open sunny spots such as on walking paths or exposed rocks. You're very unlikely to see a snake on a very hot day; they'll be under thick rocks or underground. Snakes are also rarely seen on very cold days when there is little reason to be active.

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