The Ashdown Forest Conservators say one of their regular dog walkers reported her dog was bitten by an adder on Tuesday.
The dog was taken to the vet. Conservators say people should be aware that as the weather improves the adders start to stir.
They are slow and sluggish as they warm themselves on the edges of firebreaks, ponds and bare patches of ground.
As they are slow they can’t get out of the way if sniffed or trodden on - so they bite in defence - so please keep your dogs in close observation at all times just in case.
Also never try and pick up an adder - it will bite.