The Berg Adder has blotches down the back that are usually paired and triangular (resembling a butterflies open wings) and often they have a pale line bordering the blotches. The head has an arrow shaped pattern on the top (this can be quite feint in some of the colour forms)

Puff Adders have chevron markings (>>) down the body, becoming bars towards the tail section. They have a line between the eyes on the top of the head.

It’s easy to confuse a Berg Adder with a Puff Adder. The graphic below illustrates how to recognize the key differences between the two species.