The 44-second long video, filmed near Portling, shows the adder near a beach in August - but the video has only recently started gaining views online.
In the video, the adder can be heard hissing as a bystander wonders aloud if it might be pregnant.
Adders are normally found across the UK, with the exception of Scottish islands.
Britain’s only venomous snake, the adder is of little danger to humans.
Its bite can be painful and leave a nasty inflammation but adders are generally dangerous to the very young, ill, or elderly.
They are relatively shy animals who will keep themselves to themselves, and will only attack when trodden on or picked up.