The oldest form of the name is eft, which is still used for newly metamorphosed juveniles, but according to the Oxford English Dictionary it changed for unknown reasons first to euft and then to ewt. For some time it remained as an ewt, but the "n" from the indefinite article an shifted to form a newt.
The three common European genera are the crested newts (Triturus sp.), the smooth newts and palmate newts (Lissotriton sp.) and the banded newts (Ommatotriton sp.). Other species present in Europe are the Iberian ribbed newt (Plurodeles waltl), which is the largest of the European newts, the pyrenean brook newt (Calotriton sp.); the European brook newt (Euproctus sp.) and the Alpine newt (Mesotriton alpestris).
In North America, there are the Eastern newts (Notophthalmus sp.), of which the red-spotted newt (Notophthalmus viridescens) is the most abundant species, but it is limited to the area east of the Rocky Mountains. The three species of coastal or Western newts are the red-bellied newt, the California newt, and the rough-skinned newt, all of which belong to the genus Taricha, which is confined to the area west of the Rockies.
In Southeast Asia and Japan, species commonly encountered in the pet trade include the fire belly newts (Cynops sp.), the paddletail newts (Pachytriton sp.), the crocodile newts (Tylototriton sp.), and the warty newts (Paramesotriton sp.). In the Middle East there are the middle eastern newts (Neurergus sp.).
Like all members of the order Caudata, newts are characterised by a lizard-like body with four equal sized limbs and a distinct tail. Aquatic larvae have true teeth on both upper and lower jaws and external gills. They have the ability to regenerate limbs, eyes, spinal cords, hearts, intestines, and upper and lower jaws. The cells at the site of the injury have the ability to de-differentiate, reproduce rapidly, and differentiate again to create a new limb or organ. One theory is that the de-differentiated cells are related to tumour cells since chemicals which produce tumours in other animals will produce additional limbs in newts. Many newts produce toxins in their skin secretions as a defense mechanism against predators. Taricha newts of western North America are particularly toxic; the Rough-skinned newt (Taricha granulosa) of the Pacific Northwest produces more than enough tetrodotoxin to kill an adult human. In order to cause harm, the toxins have to enter the body by being ingested or entering a break in the skin.
The main breeding season for newts is between the months of February and June. After courtship rituals of varying complexity, which take place in ponds or slow moving streams, the eggs are fertilised outside the female's body and attached, singly, to the leaves of aquatic plants. The plant leaves are usually folded over and adhered to the eggs to protect them. The tadpoles, which resemble fish fry but are distinguished by their feathery external gills, hatch in about three weeks. After hatching they eat algae, small invertebrates or other tadpoles. During the next few months the tadpoles undergo metamorphosis, during which they develop legs, and the gills change into air-breathing lungs.Some species, such as the North American newts, also become more brightly coloured during this phase. Once fully metamorphosised they leave the water and live a terrestrial life, when they are known as "efts". Only when the eft reaches adulthood will the North American species return to live in water, rarely venturing back onto the land. Conversely, most European species live their adult lives on land and only visit water to breed.
Although newts have a toxin on their skin, most newts can be safely handled, provided that the toxins they produce are not ingested or allowed to come in contact with mucous membranes or breaks in the skin. After handling, proper hand-washing techniques should be followed due to the risk from the toxins they produce and bacteria they carry, such as salmonella. . It is, however, illegal to handle or disturb Great Crested Newts in the UK without a licence. A 29-year-old man in Coos Bay, Oregon, who had been drinking heavily, swallowed a rough-skin newt Taricha granulosa for a dare. He died later that day despite hospital treatment.
Folklore held that pigs in England could eat newts with impunity, while their French porcine cousins would die a horrible death from the same ingestion.. Some Native Americans of the Pacific Northwest used Taricha newts to poison their enemies.
In Europe, nine newts are listed as "strictly protrected fauna species" under appendix II of the Convention on the Conservation of European Wildlife and Natural Habitats:
The remaining European species are listed as "protected fauna species" under appendix III.