Gardens shelter snakes and lizards

I know that my garden supports a small number of frogs and toads. While the frogs were quick to lay claim to my new wildlife pond, spawning in the first spring after the pond had been dug, the toads show a more terrestrial existence, most often appearing on the patio on damp nights to frighten the dogs. The fact that our garden is walled on three sides and located in the middle of town, is probably sufficient reason for the lack of any other amphibians or reptiles. It is known that only the common frog readily penetrates the urban landscape, possibly because of its greater dispersive powers or, more likely, because it is assisted by householders moving spawn from one pond to another.

It seems that the range of reptiles and amphibians you can attract into your garden is, to a greater extent, determined by where your garden is located and the nature of the habitats that surround it. There are some gardens, recently built on former heathland sites in Dorset, that have visiting Adders and Smooth Snakes, the latter a rare species these days. Other rural gardens might support a thriving population of Great Crested Newts or Grass Snakes, and I know of gardens in Norfolk that have both. Less common in most Norfolk gardens is the Slow-worm, not a worm but a legless lizard, with a beautifully patterned body (in the case of the adult males).

Recent research has underlined that the features you have within your garden can also have an influence on which amphibian and reptile species you can support. Open compost heaps are used by Grass Snakes, the elevated temperatures within the mound of decomposing vegetable material help the Grass Snake’s eggs to develop, while stacks of logs and piles of rubble provide shelter for this and other species. There is a garden just down the road from here where the owner has placed sheets of corrugated tin at various points around his large, wooded garden, He now has an impressively large population of Grass Snakes and Slow-worms.

If you are an active gardener like me, then you are more likely to stumble across one of these garden-dwelling reptiles or amphibians but in many gardens they will go unnoticed. Having said this, cat owners sometimes find that their pet has delivered some unfortunate frog, Slow-worm or Grass Snake, which would otherwise have gone unnoticed. The impact of cat predation on some of our reptile and amphibian species might be quite significant, at least in terms of the numbers killed each year. There are likely to be other risks (lawn mowers and garden chemicals to name but two) so the garden can be a difficult place for some species.

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.

A fortunate find

The Slow-worm is one of those creatures which I rarely stumble across these days, perhaps because it spends the greater part of the year hiding underground or in deep cover. Being ‘cold-blooded’ the Slow-worm tends to thermoregulate by keeping its body in contact with warm surfaces. While our three snakes tend to bask out in the open, the Slow-worm will often warm itself by settling under a piece of tin or other refuse that absorbs the sun’s warmth. Of course, it is with the snakes that the Slow-worm is sometimes confused; despite its cylindrical body and absence of external legs, the Slow-worm is not a snake but a harmless ‘legless’ lizard. Unfortunately, ignorant householders, panicked by the ‘snake-like’ appearance, may soon dispatch any Slow-worm that turns up in their garden. This is not only bad for the Slow-worm but also for the gardener, because Slow-worms eat good numbers of common garden pests, like slugs. Slow-worms differ from snakes in having a visible eyelid and smooth body scales. In addition, the cylindrical body shape is uniform along most of its length, whereas in a snake there is a clear narrowing behind the head to produce a discernable ‘neck’.

Hibernation ends in March and throughout the spring adult Slow-worms indulge in breeding. Mating is a fairly aggressive affair, with the adult males grabbing and holding females by their head. The resulting young are ‘born’ in September or October, hatching from their eggs almost immediately they are laid, giving the appearance of live birth. These young Slow-worms are just eight or nine centimetres in length and have the colour of newly minted metal. As adults they become a shiny metallic grey-brown, like well-aged bronze, often with thin longitudinal stripes of chocolate brown. Some of the older males are adorned by a pattern of pale blue spots, scattered along their head and flanks.

My most recent Slow-worm encounter happened just the other week and was unusual in that the lizard was out in the open, part way across a gravel track. I normally encounter them when turning over sheets of corrugated tin or refuse on areas of rough grassland or heathland. This particular individual had clearly shed its tail at some point in the past, either lost during courtship or shed to distract a would-be predator. The tail is physically shed (as opposed to being pulled off) by the lizard, muscular contractions pulling apart the tail at a point of fracture within the vertebrae. Once shed, the tail will flex and spasm for several seconds, sufficient distraction for the lizard itself to slip away. I managed to take a few photographs and then the Slow-worm was gone, disappearing into thick cover.