Newts belong to an order called the Urodeles, containing those species commonly described as the ‘tailed’ amphibians, as opposed to the frogs and toads that are the ‘tail-less’ amphibians.
The Urodeles consists of newts and salamanders. In a strict zoological sense these two terms are rather ill-defined, although those species that have a laterally compressed tail, making it flat and oar-shaped, are usually referred to as newts. Those that have a tail that is round in section are usually referred to as salamanders. The three native British species; the smooth newt Lissotriton vulgaris, the palmate newt Lissotriton helveticus, and the great crested newt Triturus cristatus, all belong in the family Salamandridae, but with their laterally compressed tails are universally referred to as newts.
The annual cycle is similar for all three species. The winter months are spent in hibernation which, for the majority, occurs on land, although a few individuals may over-winter in the bottom of ponds. Emergence begins early in the year and newts make their way to their breeding ponds. The number of newts in the ponds gradually builds as spring progresses, so that by early to mid-April, the breeding season peaks. During the early days of spring when the males first arrive at the ponds, they undergo a transformation. Their crests and other sexual ornamentation develop and their colours are enhanced, bringing them into full breeding condition.
Whilst the primary function of the crest is to impress the females, it probably also serves a secondary function. In common with other amphibians, after metamorphosis newts breathe via lungs and have to periodically visit the water surface for a gulp of air. However, they also have permeable skins and can respire underwater through their skin. During periods when the newts are quiescent underwater this ‘cutaneous respiration’ can provide sufficient oxygen to allow them to remain submerged indefinitely allowing them, for example, to hibernate in water. It is when they are active, particularly in warm water, that they have to make frequent visits to the surface. Male newts are highly active underwater during courtship and the increased surface area of skin provided by the large crest probably allows them additional time between visits to the surface. This ensures courtship rituals need not be interrupted at the cost of losing the female to a competitor!
Unlike frogs and toads, fertilization of newt eggs occurs internally. The elaborate courtship ritual involves much posturing and tail-fanning by the male to waft his secretions towards the female. If she is receptive to his advances, the male will deposit a spermatophore, a small package of sperm cells wrapped in a membrane, on the bottom of the pond. He will then encourage her to position herself over the spermataphore, at which point she will open her cloaca and absorb the spermatophore into her body. Spawning begins soon afterwards.
Unlike the spawning behaviour of frogs and toads, newt eggs are not all laid in one explosive event. Instead they are laid individually, each being carefully wrapped in the submerged leaf of an aquatic plant for protection. The female carefully selects a suitable leaf that will be broad enough to completely envelop the egg; yet flexible enough that she will be able to fold it. The egg is covered in a sticky secretion that ensures that once laid it will adhere to the leaf. She then manipulates the leaf with her hind feet, folding it over the egg and sticking it down. Grass blades are often favoured for this purpose, evidently providing the correct shape and flexibility and it is not uncommon to find blades of aquatic grasses that have had eggs laid along their entire length, the multiple folds resulting in a characteristic concertina shaped blade, often useful for surveyors determining the presence of newts in a pond.
Only a few eggs are laid each night, although each female will produce several hundred. This means that the breeding season, and consequently the period of time that the newts remain in the ponds, is much longer than it is for frogs or toads. Newts usually remain in the ponds until June, although many of the males, having completed their contribution to the breeding cycle, may have left before this. Whilst most newts will spend the summer months on land, there are nevertheless a proportion that will choose to stay in the water beyond the breeding season, or at least visit the ponds from time to time, so small numbers of newts may be seen in ponds throughout the summer.
Once eggs are laid, the incubation period is temperature-dependent, but eggs usually begin to hatch after two to three weeks.
On hatching, the larvae are immobile and spend their time hanging from a stone or a leaf by a pair of stabilizers, or balancers, extending from their heads. However within a few days the balancers are shed and the larvae become free swimming. Newts are carnivorous throughout their lives, the smallest larvae feeding on microscopic protozoans. As they grow, they progress to small crustaceans such as Daphnia and Cyclops, then gradually to larger soft-bodied invertebrates appropriate to their body size.
As the eggs are laid over an extended period of time, development and metamorphosis are staggered, with the earliest metamorphs beginning to emerge from the ponds by midsummer. However, sometimes it seems that late hatchlings lack the required time to develop as far as metamorphosis before temperatures decline in the autumn. In this case they will overwinter in the pond as larvae, metamorphosing into adults the following year.
From an early stage in their development, newt larvae superficially resemble the adults, the principal observable difference being the presence of large branches of gills protruding from either side of the head. Consequently, although the larvae undergo a complex series of changes during metamorphosis, the process appears less dramatic in newts than it does in frogs and toads as the body shape does not change significantly; the most obvious change simply being the loss of gills.
Once metamorphosed the small, immature newts, now often referred to as ‘efts’, live a chiefly terrestrial existence, feeding and growing amongst the undergrowth. Most efts will not be found back in the ponds until they reach maturity at three years of age, when they return to breed.