There have been a number of adders sightings across the UK in recent months resulting in the deaths of numerous dogs.
There are only three types of snakes native to the UK - an adder, grass snake and a smooth snake.
Adders are the most dangerous as they are the only venomous one out of the three.
This article will help you be able to tell them apart whilst you are out and about and keep you and your canine friends safe. 
@Samox24 thank you for this enlightening article as snakes are prevalent across the World right now (except in Ireland and Hawaii) so we should all be on the lookout. Our home backs up to woods so my husband is always finding them in the yard when doing lawn work. I am scared to death of them, but he has taken to coming and getting me to look at them so I can try to learn the difference between a āgood snakeā and a ābad snakeā. So far the only one I am truly comfortable with is the King Snake which is black and white with rings on itās body. They are known to kill the ābad snakesā so I welcome them, although they are startling to run up on.
I will always believe a snake is what truly brought demise to my black lab a few years back. We took him to the emergency vet after he suddenly had a large lump (huge exactly) on his chest that appeared out of nowhere. I thought I could see fang marks but the emergency vet said it was a blocked nipple on his chest. I wish I had taken him for a second opinion as he died not too long after that.
As sitters, and as just people who enjoy the outdoors, please keep aware of you and your petās surroundings.
@Debbie-L Iām so sorry to hear that. One of our previous dogs was bitten by an adder on a morning walk and started to go downhill quickly so John coaxed and carried her back to the car and took her straight to the vets. They put her on a drip all day and had her there all day and she had to have supervision all night because grapefruit size swellings appeared on her body and moved. If one had constricted her breathing we would have had to give her the kiss of life. Very scary and she was very wary of anything snake like after that.
Yikes. I have such a fear of snakes that my instinct for any and all is to RUN.