Arran has been an island for longer than the British mainland, and the absence of a number of species from the local fauna reflects this. Grass snakes are one such notable absence, and frogs and newts are likely to be relatively recent introductions. However, the mild climate favours cold blooded creatures, and some species, such as the adder, have flourished in a habitat lacking in competitive predators such as foxes, stoats and weasels.

Moorland habitats are particularly important for reptiles and amphibians, with ample upland bog and lochains for common toads, and an abundance of field voles and insect prey for adders. On warm summer days common lizards and adders can be found basking in the sun in south facing glens such as Glen Rosa.