The male scratches the female's skin with his teeth, possibly allowing secretions from his mental gland to enter the female's bloodstream. It is hypothesized that these secretions may stimulate courtship behavior in the female. Adult and larval Northern two-lined salamanders also exhibit antipredation behavior. Garter snakes constitute a significant predatory force on the adults. Different populations and individual adults within a population display unique behavioral patterns to snake contact.
Adults touched by the body or head of a snake typically remain immobile.
However, if touched by the snake's tongue, adults may demonstrate running or jumping behavior as an alternative to an immobile response. Adults that run after touching a snake tongue also run faster than other adults in the absence of a predator. Larvae also evade predators by altering their behavior. Aquatic larvae utilize chemical cues in the water to detect the presence of predatory fish. If fish are present, larvae seek shelter and may hide for days even after the fish are no longer present.