adders

Temperature

Snakes, like many other animals, are affected by temperature. They are poikilothermic, meaning that they cannot regulate their temperature by internal means. They are therefore dependent on their surroundings and on external sources of heat. If the external temperature is too low, they cannot continue to live, and that is one reason why their geographical distribution is limited. Britain, for example, has only three snake species, one of which, the smooth snake, is extremely localised and rare. One of Britain’s three lizard species, the sand lizard, is in a similar state. The adder is unusual among snakes in its tolerance of cold, and is found further north than any other species of snake.

The optimum temperature range for seeing adders in Britain is very roughly 10 C to 16 C, though local conditions may affect the behaviour greatly. Adders do not like wind, but if they can find sheltered spots, they may be found even on very cold days, sometimes even when there are icy puddles nearby. The crucial point is whether they can gain more radiated heat from the sun than they lose through radiation, convection (increased by wind) and conduction (to the ground). Direct sunshine is not essential, as infra-red radiation and visible light can penetrate cloud.

Reptiles can gain heat energy by basking, which looks like lazy behaviour, but is a necessary behaviour. Basking adders may be quite reluctant to give up, and may occasionally be seen in light rain, still optimistically lying in a favourite spot. This may involve some balancing of probability as to whether the conditions are likely to improve soon enough to make remaining a better option than departure. Human sunbathing is utterly different from basking: because we have internal mechanisms for temperature control, basking has much less benefit for us than for reptiles. Of course, a warm day is better than a very cold one, in that less energy is required to balance heat losses, but above a certain point, increasing the temperature is counter-productive, and we may need to sweat to lose heat.

Please see the page about temperature control.