From Ohio History Central
Amphibians are the only land vertebrates that go through a metamorphosis. This transformation is easy to recognize in toads and frogs, but the change is less dramatic in salamanders and newts.
Frogs and Toads
During the breeding season, the male frog or toad will fertilize the females eggs in water. The eggs are inside a jelly-like substance that normally swells as it absorbs water.
A few days later the eggs begin to change, with a small tadpole forming inside each one. The tadpole looks like it is all head and tail. The tail is actually longer than the body. It also has external gills for breathing. When it first hatches, the tadpole is very weak and can not swim very well.
As the strength in their tail improves, it begins to wriggle its tail so it can swim.
The tadpole has two sticky-like places behind its mouth and above its belly. Using these, it will attach itself an underwater plant. A few days later, it will begin to swim around and, using rows of tiny teeth, begin to eat algae.
After approximately a month, the gills are covered over by skin. The tadpole gets oxygen from the water plants and algae that it eats. At this age they are very active.
A few weeks later, the hind legs begin to appear. As they develop more, these legs help to move the tadpole through the water. At this time, the body begins to get longer and the head takes shape. The front legs begin to appear, elbow first. The tadpole's diet changes to include dead insects and even dead tadpoles.
By the time the tadpole is nine-weeks old, the tadpole is now considered a froglet. It looks like a miniature frog or toad but still has the long tadpole tail. The tail is slowly absorbed into the body. Froglets begin to gather around the edges of the pond.
The metamorphosis usually takes 12 - 16 weeks. Climate and water temperature have a lot to do with this process. Some frogs and toads that live in colder climates may stay tadpoles longer, evening overwintering in this stage until spring.
Once the tail is completely absorbed, the young frogs and toads will come on land. Depending on the species, this may be the last time it is near water until it is ready to breed and start the process over again.
Salamanders and Newts
The metamorphosis of newts and salamanders is very similar to frogs and toads. However, the larval form looks a lot like the adult.
Eggs can be laid in water and left alone. However, Many salamanders do not have a free-living larval stage. The eggs can be laid on land and guarded by either parent, like the Northern dusky salamander, or kept inside the female to develop.
When eggs that are laid in water hatch, they look little like a tadpole but the eye is much larger and there are three pairs of feathery gills instead of the tadpole's two.
The young feed on water fleas and bloodworms.
The front legs begin to appear within the first eight weeks. This is different from the back legs forming first on frogs and toads.
Soon the body begins to grow and take on the shape of the adult salamander or newt. The back legs are smaller than the front. Some amphibians, like the mudpuppy never develop past this stage.
For those species that continue to develop, they in time look just like the adult except for tiny gill remnants that will eventually disappear. Young salamanders will feed on anything that they can find at this stage.
Most salamanders when, they become an adult, will leave the water and live nearby on land, returning to the water during breeding season. The exception to this is the red spotted newt. This newt will leave the water as a red eft and live on land for around three years. At this time metamorphosis begins and it returns to the water as the adult red spotted newt.