A sunny day in April is good. I've seen males in combat around April/May in Yorkshire. Can't remember the actual date Keith is referring to although I was with him on the day as it was a BF meet. Keith will know.
they are quite common in my part of the world, also grass snakes, which are larger and olive green, and will also rise up and hiss if cornered, although harmless. Common lizards and slow worms as well, and rarer sand lizard and smooth snake.
Adders usually get out of your way, the danger lies in treading on one, or attempts to pick the snake up. They can be a bit dopy at the beginning and the end of their active season (due to cool days), so care needs to be taken then. While not necessary lethal to humans, an adder bite can be fatal to a dog.
I know one person bitten by an adder, the tennis net had been taken down in preperation for the winter, and a sudden shower occurred, so he picked up the net to put it under cover. An adder must have taken refuge in the net, and becoming trapped, bit him. Noone saw the snake, but the bite marks were there, and his arm swelled up.
yes, I know someone whose dog was bitten by an adder, as soon as the vet was contacted, the order was "bring the dog to the surgery IMMEDIATELY" and was waiting in the car park with a syringe of antidote.
The weather we are having now is just the sort where care needs to be taken - they have been lured out of hibernation by the warm spell, now the temperature has suddenly dropped