A newt is a semiaquatic amphibian of the family Salamandridae, although not all aquatic salamanders are considered newts. Newts are classified as a part of the salamandrid subfamily Pleurodelinae, and can be found in North America, Europe and Asia.
Newts metamorphose through three distinct developmental life stages: aquatic larva, terrestrial juvenile (called an eft), and adult. Adult newts have lizard-like bodies and may be either fully aquatic, living permanently in the water, or semiaquatic, living terrestrially, but returning to the water every year to breed.
Newts are found across Europe, North America, Asia and Japan but a number of populations are threatened due to pollution or destruction of their breeding sites and terrestrial habitats.
The Old English name of the animal was efte, efeta (of unknown origin), resulting in Middle English eft; this word was transformed irregularly into euft, evete, or ewt(e). The initial 'n' was added from the indefinite article 'an' by provection (juncture loss) by the early 15th century.The form 'newt' appears to have arisen as a dialectal variant of eft in Staffordshire, but entered Standard English by the Early Modern period (used by Shakespeare in Macbeth iv.1). The regular form eft, now only used for newly metamorphosed specimens, survived alongside newt, especially in composition, the larva being called "water-eft" and the mature form "land-eft" well into the 18th century, but use of the simplex "eft" as equivalent to "water-eft" has been in use since at least the 17th century.
Dialectal English and Scots also has the word ask (also awsk, esk in Scots) used for both newts and wall lizards, from Old English āþexe, from Proto-Germanic *agiþahsijǭ, literally "lizard-badger" or "distaff-like lizard" (compare German Eidechse and Echse, both "lizard"; *agi- is ultimately cognate with Greek ὄφις "snake", from Proto-Indo-European *h₁ogʷʰis). Latin had the name stellio for a type of spotted newt, now used for species of the Stellagama genus. Ancient Greek had the name κορδύλος, presumably for the water newt (immature newt, eft). German has Molch, from Middle High German mol, wikt:olm, like the English term of unknown etymology.
Newts are also known as Tritones (viz., named for the mythological Triton) in historical literature, and "triton" remains in use as common name in some Romance languages, in Greek, and in Russian. The systematic name Tritones was introduced alongside Pleurodelinae by Tschudi in 1838, based on the type genus named Triton by Laurenti in 1768. Laurenti's Triton was renamed to Triturus ("Triton-tail") by Rafinesque in 1815. Tschudi's Pleurodelinae is based on the type genus Pleurodeles (ribbed newt) named by Michahelles in 1830 (the name meaning "having prominent ribs", formed from πλευρά "ribs" and δῆλος "conspicuous").
The three common European genera are the crested newts (Triturus spp.), the smooth and palmate newts (Lissotriton spp.), and the banded newts (Ommatotriton spp.). 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 spp.) and the alpine newt (Ichtyosaura alpestris).
In North America, the eastern newts (Notophthalmus spp.) include the red-spotted newt (Notophthalmus viridescens), which 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 spp. and Hypselotriton spp.), the paddle-tail newts (Pachytriton spp.), the crocodile newts (Tylototriton spp.), and the warty newts (Paramesotriton spp.). In the Middle East are the spotted newts (Neurergus spp.).
Newts share many of the characteristics of their salamander kin, Caudata, including semipermeable glandular skin, four equal-sized limbs, and a distinct tail. The newt's skin, however, is not as smooth as that of other salamanders. 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 Japanese fire belly newt can regenerate its eye lens 18 times over a period of 16 years and retain its structural and functional properties. The cells at the site of the injury have the ability to undifferentiate, reproduce rapidly, and differentiate again to create a new limb or organ. One hypothesis is that the undifferentiated cells are related to tumour cells, since chemicals that produce tumours in other animals will produce additional limbs in newts.
The main breeding season for newts is (in the Northern Hemisphere) in June and July. After courtship rituals of varying complexity, which take place in ponds or slow-moving streams, the male newt transfers a spermatophore, which is taken up by the female. Fertilized eggs are laid singly and are usually attached to aquatic plants. This distinguishes them from the free-floating eggs of frogs or toads, which are laid in clumps or in strings. Plant leaves are usually folded over and attached to the eggs to protect them. The tadpoles, which resemble fish fry but are distinguished by their feathery external gills, hatch out in about three weeks. After hatching, they eat algae, small invertebrates, or other tadpoles.
During the subsequent few months, the tadpoles undergo metamorphosis, during which they develop legs, and the gills are absorbed and replaced by 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.
Many newts produce toxins in their skin secretions as a defence 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, and some Native Americans of the Pacific Northwest used the toxin to poison their enemies. However, the toxins are only dangerous if ingested, and the newts can easily and safely live in the same ponds or streams as frogs and other amphibians, or be safely kept as pets. The only predators of Taricha newts are garter snakes, some having developed a resistance to the poison. Most newts can be safely handled, provided 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.
About two-thirds of all species of the family Salamandridae, comprising these genera, are commonly called "newts":
- Calotriton Spanish brook newts
- Cynops firebelly newts
- Echinotriton spiny newts
- Ichthyosaura alpine newts
- Lissotriton small-bodied newts
- Neurergus spotted newts
- Notophthalmus eastern newts
- Ommatotriton banded newts
- Pachytriton paddle-tail newts
- Paramesotriton warty newts
- Pleurodeles ribbed newts
- Taricha Pacific newts
- Triturus crested newts
- Tylototriton crocodile newts
The term "newt" has traditionally been seen as an exclusively functional term for salamanders living in water, and not a systematic unit. The relationship between the genera has been uncertain, although they have been suggested to constitute a natural systematic unit and newer molecular analyses tend to support this position. Newts only appear in one subfamily of salamanders, the Pleurodelinae (of the family Salamandridae), however, Salamandrina and Euproctus, which are sometimes listed as Pleurodelinae, are not newts. Whether these are basal to the subfamily (and thus the sister group of the newt group) or derived, making the newts an evolutionary grade (an "incomplete" systematic unit, where not all branches of the family tree belong to the group) is currently not known.
Some newt populations in Europe have decreased because of pollution or destruction of their breeding sites and terrestrial habitats, and countries such as the UK have taken steps to halt their declines. In the UK, they are protected under the Wildlife and Countryside Act 1981 and the Habitat Regulations Act 1994. It is illegal to catch, possess, or handle great crested newts without a licence, or to cause them harm or death, or to disturb their habitat in any way. The IUCN Red List categorises the species as ‘lower risk’ Although the other UK species, the smooth newt and palmate newt are not listed, the sale of either species is prohibited under the Wildlife and Countryside Act, 1981.
In Europe, nine newts are listed as "strictly protected 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.
Newts, as with salamanders in general and other amphibians, serve as bioindicators because of their thin, sensitive skin and evidence of their presence (or absence) can serve as an indicator of the health of the environment. Most species are highly sensitive to subtle changes in the pH level of the streams and lakes where they live. Because their skin is permeable to water, they absorb oxygen and other substances they need through their skin. Scientists study the stability of the amphibian population when studying the water quality of a particular body of water.
Chinese warty newts, Chinese fire belly newts, eastern newts, paddletail newts, Japanese fire belly newts, Chuxiong fire-bellied newts, Triturus species, emperor newts, Spanish ribbed newts (leucistic genes exist), and red-tailed knobby newts are some commonly seen newts in the pet trade. Some newts rarely seen in the pet trade are Rough-skinned newts, Kaiser's spotted newts, Banded newts and Yellow-spotted newts.