In old European tradition the adder is the snake in the heather. It is read as hidden danger on a familiar path and as caution in the open countryside of life.
Does the traditional reading fit your dream, or did it mean something else to you?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.