Eggs hatch into gilled aquatic larvae in spring. Rather than becoming aquatic adults directly, most larvae transform into the red eft, a terrestrial juvenile with rough, dry-looking skin and vivid orange colouration. Efts leave the pond and live in moist woodland for a period usually given as one to several years, foraging by day in ways aquatic newts do not.
The eft then undergoes a second transformation, returning to water with a laterally compressed swimming tail and smoother skin, and breeding as an adult. The orange colouration is aposematic: eastern newts carry tetrodotoxin in their skin, and the eft stage is more toxic than the adult, which fits an animal exposed to predators in the open.
The three-stage pattern is not obligatory. In some populations, particularly where ponds are permanent or habitat is unsuitable on land, the eft stage is shortened or skipped, and some populations retain gills into adulthood. Efts are also often mistaken for a separate species.