Once, several years ago, walking alone between North Wraxall and Castle Combe on a muddy footpath in a damp valley lined with moss and hart’s tongue ferns, I saw a grass snake coiled on the path.

In my memory, it was huge – as thick as my forearm, darkish green, looped like a piece of rope. They are the largest British reptile and can reach 80cm in length so perhaps my remembering is not too far off, though I vividly remember the shock of the encounter and the almost out of body sensation, recognising that this was not the cosy countryside, but a natural world where other inhabitants, stranger to me than deer or foxes, led their lives.

What I should have done – and what I would do now if I happened to be lucky enough to see another grass snake – is recorded the sighting with the Wiltshire & Swindon Biological Records Centre (WSBRC).

The centre and the Wiltshire Amphibian and Reptile Group have recently published The Herpetofauna of Wiltshire – the first document to outline the distribution of the county’s reptile and amphibian populations. But this first edition is just the beginning. They hope it will increase understanding of the current distribution in the county and focus future survey and recording efforts. Lead author and consultant ecologist Gareth Harris wants to find out more about the county’s snakes, lizards, frogs, toads and newts and for this, the WSBRC needs the keen eyes of gardeners and nature enthusiasts.

“Some organisations have published nice glossy hard-backed books that can be sold,” he said. “And that’s good. However, in my opinion, within weeks these books are out of date and they can be quite expensive. Our atlas can be continually and easily updated when we receive new data.”

Much of the data in the atlas had been supplied by ecological consultants who undertook surveys as part of a planning application, so it is possible the data reveals more about the distribution of developments than the distribution of herpetofauna, he explained. So the more data the centre can gather from across the county, the more accurate a picture will be.

Wiltshire supports the four species of native common and widespread reptiles found in the UK, which are the slow worm, common lizard, grass snake and adder, as well as all five species of native amphibian - the common frog, common toad, smooth newt, palmate newt and great crested newt. At least three non-native species have been recorded including American bullfrog, Alpine newt and red-eared terrapin.

“We need to know more!” Gareth said. “We need to be engaging with the community, with gardeners and converting what they know into records we can use.”

The distribution of the adder, for example, seems relatively sparse judging by the data in the atlas. But Gareth said he had heard anecdotal evidence they were had been observed more widely than the official information suggested.

“There’s a very big question mark over the adder,” he said. “In the New Forest they are doing pretty well, but we do not seem to have them on Salisbury Plain. They have been seen in Savernake Forest – more adder watching is needed.”

He said the Great Crested Newt was also doing fairly well, having been recorded in the water park and along the Bristol Avon valley.

These clay valleys are also providing a good habitat for grass snakes, while Salisbury Plain has a good number of common lizards. Slow worms have also been observed frequently in the Swindon area – perhaps because they like warmth and can often be found snuggled up in a cosy compost bin.

“Wiltshire offers diverse habitats for each of the common and widespread species in the UK, ranging from the ponds of the clay vales for great crested newt, the wetlands of the Cotswold Water Park for toad and grass snake, the ephemeral ponds of the Salisbury Plain chalk plateau for common toad and great crested newt, and the chalk hilltops for common lizard,” Gareth said.

The work of Ian Perkins, of the Imber Conservation Group, contributed data on the surprisingly large number of toads and fairy shrimp on Salisbury Plain – and helped develop understand of how the species had adapted to a changing environment.

“There are dew ponds where the cattle would drink, and so would carry eggs from the fairy shrimp around the place on their legs. Now we think they are moved by the tracks of tanks,” Gareth said. The tanks have also contributed long ruts which create temporary puddles. Some have grown big. They are puddles and do dry up. But they support fairy shrimps.”

Over 10,000 records, covering the period 1996 to 2017, have gone into atlas, offering the most up-to-date assessment of the county’s herpetofauna to date. But more information is needed. Perhaps you have a visiting toad or frog in a wildlife pond in the garden, or you are part of a community group that regularly sees reptiles in a local wood. The more comprehensive a picture the WSBRC has, the more accurate the information they can provide to researchers, students, conservationists and developers – which all helps to protect habitats and their non-human inhabitants. You need to remember four essentials in order to provide a useful record – the precise species with its Latin and English name if you can, a precise location with a grid reference, the day, month and year of the sighting, and the name of the person who identified the creature.

The WSBRC, based at Wiltshire Wildlife Trust, is the county’s local environmental records centre and has been operating since 1975. It gathers, manages and interprets detailed information on wildlife, sites, habitats and geology and makes this available to a wide range of users. This information comes from a variety of sources including published reports, commissioned surveys and data provided by voluntary and other organisations. The new atlas was supported by Wiltshire Natural History Publications Trust.

The atlas can be downloaded, free-of-charge from the WSBRC website, wsbrc.org.uk/herpetofaunaofwiltshire. If you wish to join the effort to build a better picture of Wiltshire’s wildlife and record a sighting, visit wsbrc.org.uk.