Notophthalmus, the genus comprising the eastern newts, inhabits eastern North America. A different genus, Taricha, comprises the western newts along the Pacific coast of North America. Unlike other salamanders, the skin of newts is rough-textured, not slimy. Eastern newts are primarily aquatic; western newts are terrestrial.
The life cycle of eastern newts is complex. Females deposit their eggs into shallow surface waters. After hatching, the larvae remain aquatic for 2 to several months before transforming into brightly colored terrestrial forms, called efts. Post larval migration of efts from ponds to land may take place from July through November.
But the timing varies between populations. Efts live on land (forest floor) for 3 to 7 years. They then return to the water and assume adult characteristics. In changing from an eft to an adult, the newt develops fins and the skin changes to permit aquatic respiration.
Occasionally newts omit the terrestrial eft stage, especially in the species located in the southeast coastal plain and along the Massachusetts coast. These aquatic juveniles have the same adaptations (i.e., smooth skin and flattened tail) as the aquatic adults but are not sexually mature.
Under favorable conditions, adults are permanently aquatic; however, adults may migrate to land after breeding due to dry ponds, high water temperatures, and low oxygen tension. The life cycle of western newts does not include the eft stage.
The eastern newt (Notophthalmus viridescens) has both aquatic and terrestrial forms. The aquatic adult is usually yellowish-brown or olive-green to dark brown above, yellow below. The land-dwelling eft is orange-red to reddish-brown, and its skin contains tetrodotoxin, a neurotoxin and powerful emetic.
There are four subspecies of eastern newts:
- N. v. viridescens (red-spotted newt; ranges from Nova Scotia west to Great Lakes and south to the Gulf states).
- N. v. dorsalis (broken-striped newt; ranges along the coastal plain of the Carolinas).
- N. v. louisianensis (central newt; ranges from western Michigan to the Gulf).
- N. v. piaropicola(peninsula newt; restricted to peninsular Florida).
Neoteny occurs commonly in the peninsula and broken-striped newts. In the central newt, neoteny is frequent in the southeastern coastal plain. In the red-spotted newt, neoteny is rare. Adult eastern newts usually are 6.5 to 10.0 cm in total length. In North Carolina, N. v. dorsalisefts ranged from 2.1 to 3.8 cm snout-to-vent length (SVL).
That excludes the tail, and adults ranged from 2.0 to 4.4 cm SVL. The aquatic juveniles 1 year of age to range from 2.0 to 3.2 cm SVL. Adult eastern newts weigh approximately 2 to 3 g. Whereas the efts generally weigh 1 to 1.5 g. Neotenic newts are mature and capable of reproduction but retain the larval form, appearance, and habits.
Habitat
Larval and adult eastern newts are found in ponds, especially those with abundant submerged vegetation, and in weedy areas of lakes, marshes, ditches, backwaters, and pools of shallow slow-moving streams or other unpolluted shallow or semi-permanent water. Terrestrial efts inhabit mixed and deciduous forests and are found in moist areas, typically under damp leaves, brush piles, logs, and stumps, usually in wooded habitats. Adequate surface litter is important, especially during dry periods, because efts seldom burrow.
Eastern Newt Food Habits
Adult eastern newts are opportunistic predators that prey underwater on worms, insects and their larvae (e.g., mayfly, caddisfly, midge, and mosquito larvae), small crustaceans and mollusks, spiders, amphibian eggs, and occasionally small fish. Newts capture prey at the surface of the water and on the bottom of the pond, as well as in the water column.
The shed skin (exuvia) is eaten and may comprise greater than 5 percent of the total weight of food items of both the adult and eft diets. Snails are an important food source for the terrestrial eft. Efts feed only during rainy summer periods. In late August and September, efts often were found clustered around decaying mushrooms feeding on adult and larval dipterans. In a northern hardwood-hemlock forest in New York, the most prey of adult migrants and immature efts were from the upper litter layer, soil surface, or low vegetation.
Temperature regulation and daily activities
Adult newts are often seen foraging in shallow water, and efts are often found in large numbers on the forest floor after it rains. Efts may be found on the open forest floor even during daylight hours, but they rarely emerge if the air temperature is below 10C.
Hibernation
Most adults remain active all winter underwater on pond bottoms or in streams. Some adults overwinter on land and migrate to ponds during the spring to breed. If the water body freezes to the bottom, adults may be forced to hibernate on land or to migrate to another pool. Efts hibernate on land, burrowing under logs and debris. It is observed that efts migrated to ponds for the first time in the spring and fall.
Breeding activities and social organization. In south-central New York, breeding takes place in late winter or early spring, usually in lakes, ponds, and swamps. Ovulation and egg deposition occur over an extended period. Females overwintering on land can store sperm for at least 10 months.
Spawning underwater, the female deposits eggs singly on leaves of submerged plants, hiding and wrapping each in vegetation. The time to hatching depends on temperature. Smith (1961) found typical incubation periods to be 14 to 21 days in Illinois, whereas the incubation period observed 21 to 56 days.
Growth and metamorphosis
In late summer or early fall, the larvae transform into either aquatic juveniles or terrestrial efts that low larval density stimulated neoteny in larvae under experimental conditions. Larval growth rates were higher in ponds with low larval densities. Growth rates for aquatic juveniles are highest in the spring; however, maximum seasonal growth for the terrestrial efts occurs between June and September when the temperature is optimal for active foraging.
Home range and resources. For adult newts, the distance between capture and recapture sites to be about 7 m, indicating small home ranges. It did not find any defined home range or any territoriality for males. Most efts around a pond in Pennsylvania remained within 1.5 m of the shore. The home range for terrestrial efts in a Massachusetts woodland to be 270 m2 and located approximately 800 m from the ponds where the adults and larvae were located.
Population density. Populations of aquatic adults may reach high local densities, whereas terrestrial efts exhibit lower population densities. Recorded population densities for terrestrial efts range from 34 per hectare (ranging from 20 to 50 efts per hectare) in a North Carolina mixed deciduous forest to 300 per hectare in a Massachusetts woodland. The density of 1.4 adult newts per m2 (14,000 adult newts per hectare) in a shallow pond in North Carolina in the winter, whereas the summer population density was only 0.2 adults per m2 (2,000 adults per hectare).
Many populations of the eastern newt reach sexual maturity when the eft stage returns to the water and changes to the adult form. However, under certain conditions such as low larval density, most of the larvae present have been shown to metamorphose directly into adults or even into sexually mature larvae.
In experimental ponds, densities of 22 larvae per m2 resulted in metamorphosis to eft by the majority, while a density of 5.5 larvae per m2resulted in metamorphosis directly to the adult form or sexual maturation without metamorphosis (Harris, 1987). Adult density also influences reproduction.
The doubling adult density resulted in a reduction of offspring produced to one-quarter that produced by adults at the lower density (i.e., from 36 offspring per female in tanks containing 1.1 females per m2 to 9.7 offspring per female in tanks containing 2.2 females per m2). The adult life expectancy 2.1 breeding seasons for males and 1.7 breeding seasons for females. Amphibian blood leeches (ectoparasites) are likely to be a primary source of mortality for adults; they also prey directly on larvae.
Similar Species
The black-spotted newt (Notophthalmus meridionalis) is similar in size (7.5 to 11.0 cm) to the eastern newt. It has large black spots and is found in south Texas in ponds, lagoons, and swamps. There is no eft stage.
The striped newt (Notophthalmus perstriatus) is smaller (5.2 to 7.9 cm) than the eastern newt and ranges from southern Georgia to central Florida. It is found in almost any body of shallow, standing water.
The western newts (Taricha) are found along the Pacific coast. They do not undergo the eft stage but rather transform into land-dwelling adults that return to the water at breeding time.
Other small salamanders are similar but vary by having slimy skin and conspicuous costal grooves. They differ in life history, however; in the family Plethudontidae, all are lungless and breathe through thin, moist skin. Many are completely terrestrial.
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