Adders come out of hibernation in the spring and the recent spell of warm weather means they are already active in parts of Scotland
The snake breed is not aggressive, according to the SSPCA, but they can bite when threatened which can be painful, but rarely fatal.
In some cases, adder bites have killed dogs.
SSPCA chief superintendent Mike Flynn said: “Adders are the only venomous snake in the UK.
"Females can grow up to 750mm and males are normally slightly smaller.
“Adders come out of hibernation in spring so the recent milder weather may have caused them to be active.
“Adders are not aggressive snakes and only tend to use their venom as a last resort, for example if they are stepped on or cornered. If anyone does come across an adder while out walking we’d simply advise them to give the snake plenty of space and leave it alone.”
According to the Scottish Wildlife Trust, adders, which are a protected species, are relatively small, stocky snakes and prefer woodland, heathland and moorland habitat.
They normally hibernate from October to March, and during the warmer months they can be spotted basking in the sun on a log or under a rock.
They hunt lizards and small mammals, as well as ground-nesting birds such as skylark and meadow pipit.
A police spokesman also issued a warning about the species emerging from hibernation and said sightings have already been noted in the Tarbert area.