These snakes often occur in areas popular with walkers and dog owners in Cornwall, Devon and Dorset.
From as early as March to late Autumn visitors to moors, coastal regions and heathlands are warned to keep an eye out for them.
Adders are normally of no threat to people if left alone but if accidently trodden on or feeling threatened they will bite.
Mostly they go unnoticed and will avoid people given the option.
However, in the Spring they commonly emerge from hibernation to warm up in sheltered places and on bare ground such as paths.
It is not unusual for walkers to come across them curled up on or beside the South West Coast Path.
In most cases Adders are likely to sense approaching walkers and quickly disappear into the surrounding heather or gorse.
Nevertheless, walkers should keep an eye out ahead of them and if straying off the path check where they put their feet.
The biggest danger is to dogs off the lead and every year vets in the south west treat pets for snake bites.
When roaming off the path dogs are prone to suprising basking Adders by stepping too close to them and being bitten.
Any owner hearing their dog yelp while out walking should check for a snake bite.
This may not be immediately obvious but swelling and any discomfort shown by the dog should be treated seriously.
If in doubt dog owners should immediately take their animals to a local vet for treatment.