The Adder about to strike my lens as a means of defence. The Adder is the only venomous snake native to Britain, a highly developed venom injecting mechanism. The Adder is not a aggressive snake, but when its trap or caught or trodden on then it will strike. The effects from a bite are nausea and drowsiness, followed by severe swelling and bruising around the area of the bite. So treat Adders with respect and leave them alone. So when out walking in woods or heathland or the golf course take care where you walk.