Newts are small semi-aquatic amphibians that look like a cross between a frog and a lizard. Newts possess several interesting characteristics. For example, though they may look cute and harmless, they can be dangerous; toxins secreted through the skin as a defense mechanism could kill a person. Newts also can regrow lost limbs and organs. That ability makes them important subjects in medical studies on regeneration. Also, some newts have flown on space missions.

Newts have lizard-shaped bodies with four legs and long tails. Most have smooth and moist skin, though some species, such as rough-skinned newts have, as one might expect, rough, grainy skin. Most species have well-developed lungs, while some retain gills and are completely aquatic.

With so many species, newts come in many different sizes. They are typically smaller than 8 inches (20 centimeters), according to Encyclopedia Britannica. For example, the warty newt grows to 7 inches (18 cm) and weighs 0.22 to 0.37 ounces (6.3 to 10.6 grams).

Newts can regenerate fully functional limbs, organs and tissues, including heart muscle, components of its nervous system and the lens of its eye, according to an article in the journal Nature. Researcher hope the ability is based on a common genetic trait and is found, even in latent form, in all animals. Studies indicate, however, it may not be that simple because of the enormous size of the newt genome, which is 10 times larger than the human genome.

Many newts rely on their skin color — green, black or brown — to camouflage them and escape the notice of predators. Others are marked with bright warning colors to indicate they are toxic and would not make a good meal, according to Caudata Culture.

These newts secrete a mucus that is quite toxic. A 1966 study published in the journal Toxicon found that at least 10 species had substances called tarichatoxin and tetrodotoxin. Tetrodotoxin, or TTX, is the most poisonous nonprotein substance known to scientists and is similar to that found in pufferfish, according to Caudata Culture. It is a powerful neurotoxin that block signals from the nervous system to the muscles, so for example, it blocks the signals from your brain that tell your heart to beat.

The study found that the skin of a rough-skinned newt is poisonous enough to potentially kill 25,000 mice. The study also cited a case that involved a man in Oregon who swallowed a newt on a dare (he had been drinking heavily). After a few minutes, his lips began to tingle. Over the next two hours he began to feel numb and weak and then experienced cardiopulmonary arrest. Later that day, he died, despite hospital treatment.

In another study, published in 1974 in the journal Copeia, newt toxin entered a puncture wound on a scientist's index finger, and he suffered 30 minutes of numbness up the arm into the shoulder, and some accompanying nausea and light-headedness.

Some newts add insult to injury. Besides secreting the toxin, the Spanish ribbed newt and alligator newt push their ribs through their skin to pierce their victims, making sure the poison enters the attacker's body.

Newts are carnivores. They eat slugs, worms, small invertebrates, amphibian eggs and insects on land. Tadpoles, shrimp, aquatic insects, insect larvae and mollusks are on the menu in the water. Baby newts, called larva, can feed themselves small shrimp and insect larvae they find while swimming around.

Most newts lay eggs, and one female can lay hundreds of eggs. For example, the warty newt can lay 200 to 300 eggs, according to National Geographic. However, they lay them one at a time and attach them to aquatic plants, according to A-Z Animals. Frogs, on the other hand, lay their eggs in clumps that float close to the surface of the water. A few newt species lay their eggs on land.

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