Newts

Like salamanders, newts have a complex life cycle, the stages of which are egg, larva, and adult. Some species of newts can be distinguished from salamanders in that the newts have two distinct adult stages.

In the case of the red-spotted newt (Notophthalmus viridescens) of North America, the red eft is the stage that occurs after transformation of the aquatic larva. The red eft is bright red or orange, and is a pre-reproductive adult stage. The red eft wanders widely in forests, sometimes for several years, and is most common on moist nights. Eventually, the red eft migrates to an aquatic habitat, changes to a yellowish color, develops a broad, adult tail fin, and becomes a sexually mature, breeding adult. The migration of red efts to water has been shown to be stimulated by the presence of the pituitary hormone prolactin.

Not all populations of red-spotted newts display this type of life cycle, for some coastal populations bypass the terrestrial red eft stage, and produce breeding adults directly from larvae. These adults may retain some larval characteristics, such as gills, which is an example at neoteny, or paedomorphosis.

Courtship in some species of newts involves elaborate aquatic displays by the male. These displays are designed to entice the female newt to pass over sperm-containing spermatophores that the male has previously deposited onto the surface of the sediment. If the male is successful, the female newt picks up the spermatophore with her cloacal lips and stores the spermatophore internally, which then fertilizes her ova as they are laid singly on surfaces in the aquatic habitat.

The red eft stage of the red-spotted newt contains toxic, bad-tasting chemicals in its skin. As a result, many potential predators learn to avoid this animal, and will not eat red efts. The range of the red salamander (Pseudotriton ruber) overlaps part of the larger range of the red-spotted newt in the eastern United States. It appears that the superficially similar but non-toxic red salamander may be a mimic of the color of the red eft, taking advantage of the fact that many predators avoid this animal as food.

Newts have been shown to have a keen ability to find their way home to their natal or home pond. After they were displaced during an experiment, red-bellied newts (Taricha rivularis) studied in California proved to be capable of returning to their home stream within only one year, over a distance of up to 4.96 mi (8 km).