In awe of snakes

The other week I visited the garden of Dave Shearing to take part in some filming we were doing to promote a new survey of garden reptiles and amphibians. The garden was a wildlife haven, a formal area stocked with bird feeders and then a gate through into open woodland complete with nestboxes, wildlife pond and corrugated tin plates. The tin provided shelter for Grass Snakes and Slow-worms, both of which proved to be present in the garden in good numbers.

With a careful approach and lifting of the tin it was possible to take a close look at these two less commonly encountered creatures. While some of the snakes made a swift retreat into one of the many woodpiles that dotted the garden, others remained and seemed just as inquisitive about us as we were of them. By being able to watch the snakes in this way I was really impressed by the range of adaptations they displayed.

Snakes are not unique amongst the reptiles in being limbless but this feature does form the cornerstone of their anatomy. The long thin body places constraints on its internal structure and many of the internal organs are highly modified (or absent - most snakes have just a single functional lung). Many organs are elongated and paired organs are often arranged one behind the other, rather than side-by-side; the left kidney, for example, sits behind the right. Each of the vertebrae (and there are usually between 160 and 400 of these) has a pair of ribs attached to it. The ribs themselves articulate and can be swung forward, allowing the snake to flatten out its body to soak up more of the sun’s warmth (I often see Adders doing this) or to allow the passage of a large prey item down the digestive tract. The skull is also adapted to aid the passage of large prey, the two lower jaws not joined at the chin and allowing them to move independently of one another as well as pull apart. This is why even some of the smaller individuals we watched could have tackled an adult frog.

The survey of garden reptiles and amphibians is being organised by the British Trust for Ornithology, Froglife and the Herpetological Conservation Trust. The researchers want to find out which factors influence whether or not particular species of reptile and amphibian will use a garden. As such, they want to hear from anybody who has a garden, regardless of whether or not it contains any reptiles or amphibians. A free survey pack and identification chart can be requested by calling the BTO, by emailing gbw@bto.org or by writing to Reptile Survey, BTO, The Nunnery, Thetford, Norfolk, IP24 2PU.