Can you remember seeing an adder? If you do then the Adder Adder national survey of one of Britain's few snakes would like you to take part, writes ELIZABETH EDWARDS

"I remember seeing an adder lying on the stones at the top of that narrow lane that we walked on that hot sunny day in. Now, just when was that?" If anybody has pondered distant and more recent memories of seeing an adder, then Dr Tony Gent would like to hear from you.

He is researching how adder numbers may have dropped over recent decades and needs this past information in order to be able to make a comparison between the past and the present.

Dr Gent is from the Herpetological Conservation Trust, a national charity which specialises in the conservation of amphibians and reptiles (herpetofauna) and their habitats. The HCT has set up a website, www.adder.org.uk, on which to leave these memories to what is called Adder Adder to help build up information on the present status of the snake.

Although found all over Britain, the adder is becoming rare in some areas and is a concern for the HCT, which manages 80 nature reserves, mostly on heathland in southern Britain. It works in partnership with other national and international organisations to encourage more people to understand and appreciate herpetofauna.

This is a survey that can be done the easy way - anywhere and at any time, talking about past countryside experiences, particularly with older friends and family members who may have memories going back a long time.

Incidents are certainly likely to have been on sunny days, for Dr Gent describes adders as being "solar-powered".

"They like to get their body temperature up to 20 to 30 degrees - at 15 degrees they find if difficult to digest food," he said. "They aim to maintain their heat at 20-plus degrees, but not over 30, so they will not be out in the hottest part of the day, and not in the midday sun.

"The most likely time to see them basking, possibly in groups, is when it is reasonably warm, but not too hot. By spreading themselves out in the sun they maximise the heat cover. Several may bask together. After the dormant winter period they have to get their physiology into good condition. Body temperature is the absolute key."

They warm up very quickly in the sun and are nervous of predators and movement so don't like windy conditions and they will move away if they see an observer move. They like places with shelter in which they can hide themselves from any threat, but where they can see approaching danger.

Adders vary in colour and markings, but their dark zigzag line along the back and the V-marking on the back of the head are characteristic. The main body colour can be reddish-brown, greenish-yellow, grey or creamy buff, with the female duller and more brown, and juveniles reddish-brown. The females are longer and more plump than the males.

They shed their skins from time to time and the skins are a sign of their presence. They eat small mammals such as mice and voles, as well as lizards, frogs and toads if nothing else is available.

Adders are a protected species. Although people often have a fear of them, they bite only in defence. They may hiss if distressed or agitated.

A bite does not usually have serious consequences, but medical attention should always be sought.

Abundance of prey and of natural cover, as well as lack of human disturbance, are key factors in where they are to be found.

The HCT began collecting records about two years ago. So far around 1,780 reports have been received.

From Oxfordshire, there have been only nine. The earliest is from 1940, in the east of the county. A sighting in 1984 was in the north, and the others, all from more recent times, give a spread across the west and south as well, and within a few miles of Oxford.

In neighbouring counties, the numbers have been higher - with 24 in Berkshire, more than 40 in Buckinghamshire and as many as 75 in Gloucestershire. Searching back through their memories, people have recalled details of encounters with adders from clues such as "It was when war had just been declared", and "It was as I got off the train at x' station".

A particularly unusual memory was of an occasion when RSPCA and police officers, wearing waders, went into a swimming pool to gather up an adder.

"What we have so far received clearly does not represent all the information that is available," said Dr Gent. "We are trying to get people to send in more records.

"We have no clear idea of how adders are faring on a nationwide basis. A lot of things have happened in the countryside during the past century - changes in agriculture, increased housing, quarrying, and road and railway building. We can predict that widespread changes will have resulted."

The changed are most likely in the southeast and the Midlands.

The preferred habitat of adders is tussocky grass, such as on ungrazed paddocks, and where there are hedges where they can find prey. The wide field margins left when farmers take part in environmental stewardship schemes are helpful to adders. In more open country, heaths, moors, scrub-covered hills and coastal dunes are all favoured places.

An adder can have a quite wide range in its own territory, up to as much as a mile. The more damp places, which offer better feeding opportunities, are often sought out, and for the benefits for basking that it can provide, a south-facing railway embankment is ideal.

"It is said that many people have never seen a snake - and probably that is not far wrong," said Dr Gent. "It would be interesting to know what the percentage is. It may be only about 50 per cent, and then people may only have seen a snake once or twice, and that a long time ago.

"But we do want people to send in more reports. We want data that may even be secondhand. All these stories will help in piecing things together; the more records that people can give us, the better."

Looking back on historical associations, Dr Gent and his colleagues have researched the relevance of place name to the species they study.

Oxfordshire might be thought to have a village that once swarmed with adders, but they found that Adderbury takes its name from having been the stronghold in earlier times of a lady landowner by the name of Eadburgh. On the other hand, Netherfield in Sussex may well have been a stronghold of adders, as the Old English word for adder is naeddre', and an earlier name of the village was Nedrefelle.

Any reports of adders in Oxfordshire, or of colonies, will be welcomed at the Herpetological Conservation Trust. They will help to relate the present status of the adder to that of its past and towards consideration of conservation programmes for the future.