If you are like most kids, you have probably met an amphibian even if you did not know it. Ever caught a frog or a toad? Then you have met an amphibian! Amphibians are often lumped together with reptiles even though they are very different.
The word amphibian means “double life”. This refers to the fact that these animals need both water and land during their life cycle. They start life in the water and wind up on land as adults. Five different kinds of animals are amphibians: frogs, toads, salamanders, newts and caecilians.
If you go looking for amphibians, you can find them all over the world except in Greenland and Antarctica. In fact, Over 7,000 different species of amphibian have been found worldwide. And the amphibian you are most likely to find is a frog. Over 6,000 species of frogs have been identified, making frogs the most common kind of amphibian in the world.
Here in Idaho, we have frogs, toads and salamanders. Newts, which are another kind of salamander, are found elsewhere in the United States. The 200+ species of caecilians are found only in tropical regions.
Amphibians have been around a long time. The earliest known amphibian fossil dates from 368 million years ago! This means that this amphibian was living back in the Jurassic Period. It was found in Scotland and is called Elginerpeton. While amphibians have gotten smaller since then, some of them are still pretty big. How would you like to find a salamander that can get up to six feet long? This big guy is called the Chinese Giant Salamander. The world's smallest amphibian is the Monte Iberia Eleuth. This tiny amphibian is only ⅜ of an inch long!
All amphibians begin life in the water, but even as adults they still like wet places and need water. Frogs are often found around ponds and marshes. Salamanders and newts like damp places under logs or in wet vegetation. Their skin stays moist because of a protective mucus layer. This mucus layer also helps some amphibians breathe through their skin.
In fact, the Coeur d'Alene Salamander found here in Idaho has no lungs! It does all its breathing through its skin. Being able to get oxygen through the skin is also an advantage for amphibians that hibernate in wet places. But these are not the only things that are great about having slimy skin! It can also help an amphibian escape from enemies. Have you ever tried to hold on to a slippery frog?
EWW . . . YUCK!
Amphibians also have other defenses. Toads have glands on their body that secrete a toxin called “bufotoxin.” While this may sound like something Harry Potter would make in Potions class, it is very important to toads. Bufotoxin is very irritating to mucus membranes. If a predator picks up a toad in its mouth, not only will the toad taste terrible but the bufotoxin will also irritate the animal's mouth making it drop the toad. If the animal tries to eat the toad, the bufotoxin can make it very sick. It usually only takes one time for an animal to learn to leave toads alone!
Some salamanders also have glands that secrete toxins. The poison dart frogs of South America are very poisonous. They advertise this fact by being very brightly colored.
While most amphibians have some kind of poison glands, many rely on camouflage to stay safe. Frogs are the best example of amphibian camouflage. Their skin color and patterns mimic their surroundings. Some frogs can even change the color of their skin to match the surroundings. But even while they are hidden, frogs can still keep watch for enemies.
Because their eyes and nose are on top of their head, frogs can sit under the water with only their eyes and nose showing.
Even if a predator sees a frog in spite of its camouflage, the frog can still rely on its legs to get away. Frog legs are made for jumping. Many frogs can jump 20 times their own body length in one jump. African Frogs can leap 14 feet in one jump. How far could you jump if you were a frog?
Amphibians begin breeding in the spring. Exactly when breeding begins depends upon temperature and moisture. Since amphibians are ectothermic or cold-blooded, it needs to be warm enough for the adults to be active before breeding starts. Adult amphibians attract each other in several ways. Frogs and toads sing. In fact, the courtship calls of a group of frogs or toads can be quite loud. Salamanders, on the other hand, use visual signals like waving their tails or bobbing up and down.
Females lay their eggs in water or in the case of some salamanders in a wet area on land. All amphibians go through three stages of development — egg, larvae and adult. This development process is called metamorphosis.
Amphibian eggs are laid in masses. Each egg is covered by a jelly-like layer that protects it. The number of eggs a female can lay depends upon the species. Some frogs can lay as many as 4,000 eggs.
How quickly the eggs develop depends upon the temperature of the water. Warmer water means faster development while cold water means slower development.
The Tailed Frog that lives in cold streams in Idaho's mountains develops very slowly, taking as long as four years to become an adult. Most frogs complete their development in several months.
Larval amphibians look very different from their parents. They have tails, gills for breathing, and no legs. During the larval stage, these amphibians are mostly herbivores, eating plants that grow in the water. As they grow, their tails get smaller and they develop legs. Inside their bodies, lungs are growing so they can live on land. Finally, they leave the water.
A group of salamanders, called sirens, never develop beyond the larval stage and remain in the water their entire lives.
Some kinds of amphibians have evolved some pretty amazing ways of reproducing. While most amphibian parents play no role in raising their offspring, the male Darwin's Frog takes special care of his mate's eggs. He keeps them in his mouth until they have developed into fully grown froglets! The female Marsupial Frog keeps her eggs in a brood pouch on her back until they are grown. Asian tree frogs build nests over the water so when their tadpoles hatch they fall right into the water.
What's for Dinner?
Amphibians are herbivores as larvae and carnivores as adults. Larval amphibians feed on algae and other aquatic plants. As they get closer to becoming adults, they start eating aquaticinvertebrates like mosquito larvae. Once they develop into adults, just about anything that moves can be dinner for an amphibian.
Small amphibians feed upon small insects and other invertebrates such as worms. Larger amphibians feed upon larger insects and invertebrates. Very large species such as the Bullfrog and Idaho Giant Salamander eat a wide variety of animals including invertebrates, snakes, shrews, mice, fish and other amphibians.
In fact, amphibians are a very important control on many species we consider pests, especially insects. Most of our amphibians can pack away a lot of insects at one time. Woodhouse's Toad can eat up to two-thirds of its body weight each day. That may not seem like much, but having a toad or two living in your garden for the summer will help control a lot of the insect pests trying to eat your flowers and vegetables.
A fun way to observe toads is to watch for them at night as they feed. Find a place with a big outside light that is attracting flying insects. Nearby toads are often attracted by the insects and will come to feast underneath the light.
When we think of animals that sing, we usually think of birds. But frogs and toads are also great singers. Like birds, frogs and toads sing for several reasons. The first is to attract a mate. Most singing occurs in the spring when the breeding season is about to begin. Male frogs and toads gather sometimes in large groups in and around a pond or other area of standing water. In both the early morning and evening, they will sing to attract a mate. Some of these gatherings are so loud that you wonder how the females can ever pick out a single male among all those singing!
Frogs and toads have very complex sound production systems. If you ever watch a frog sing, you immediately notice the big bubble that forms under the animal's chin. This is the vocal sac and it functions to produce sound. Most frogs and toads have a single round vocal sac, but others have a sausage-shaped vocal sac. Some species even have two vocal sacs.
Because frogs and toads use sound to communicate, they must also be able to hear one another very well. As it turns out, these amphibians have complex systems for hearing the calls and songs of other amphibians. Not does this help frogs and toads find a mate but it also helps them stay safe. The sounds frogs and toads make are also used as self-defense as well as a warning for other frogs. Being able to hear the warning or defense calls of a frog or toad will help another frog or toad to avoid danger.
Identifying frogs and toads by their calls can be a fun and challenging way to enjoy some outside time. Most species have very distinctive songs and, with practice, you can learn to tell them apart. The first step is to find a nearby pond where frogs or toads might live. Then, as spring approaches, begin visiting the pond in the early morning and evening. Remember to be very quiet as you approach and find a good place where you can sit and listen. Bring a notebook and pencil to write down what you think the songs sound like. Later, you can compare your notes to the descriptions of songs in a field guide to frog and toad songs.
In general, amphibians are animals that like things nice and warm. You do not find any amphibians outside enjoying a winter snowstorm, and many of them do not like the summer heat either. So, what do they do and where do they go?
Just about the time we are getting out our winter sweaters, amphibians are going into hibernation. Many amphibians, especially frogs and toads, hibernate in the mud at the bottom of ponds and lakes. Because they can absorb oxygen right through their skin, they can spend the winter under the water. The mud and water act as insulation so the frogs do not freeze.
The tree frogs and a few other ground-dwelling frogs do not hibernate underwater. Instead, this group of frogs hibernates on land. Because they do not have the insulating layer of water above them, these frogs could freeze during the coldest winter months. To help protect them from freezing, a number of these frogs produce their own antifreeze. This antifreeze is made up of specialized proteins and glucose. It allows wood frogs to have 35%–45% of their body freeze without causing any problems. If it were not for its ability to makes its own antifreeze, the wood frog would not be able to live north of the Arctic Circle. Wood frogs live farther north than any other amphibian in the world.
While most amphibians like warm weather, some species that are desert dwellers actually hibernate in the summer to beat the heat. Because amphibians are cold-blooded or ectothermic, their bodies can heat up very quickly. To avoid the heat, they become active at night and spend the day in the shade. But in the heat of the summer, it can become too hot even at night. Then these species dig a nice deep burrow and spend the summer in a kind of hibernation called aestivation.
Here in Idaho the Great Basin Spadefoot toad is the species that is best known for aestivation. Their burrows can be as deep as 3 feet underground. Here they stay cool when it is very hot. These burrows are also used for winter hibernation. Spadefoot toads can spend 6–8 months of each year in their burrows either hibernating or aestivating.
Because of Idaho's varied landscape and climate, the state has a small but interesting variety of amphibians. In all, fourteen species of amphibians — four salamanders, seven frogs, and three toads — live in our state.
The largest amphibian in Idaho is the Idaho Giant Salamander. It can grow to be 8 inches long and lives in northern Idaho. These large salamanders can be found living in moist forests at elevations of up to 7,000 feet. Our other three species of salamander are the Long-toed, the Tiger and the Coeur d'Alene salamander.
One of our most interesting amphibians is the Tailed frog. These small frogs can be found in cold-water mountain streams of the central part of the state. Their name comes from a small tail found on the males. This tail is used for breeding. Tailed frogs do not have eardrums and have never been heard making any kind of sound. Living in and near a loud rushing stream would not make it easy to hear a sound or be heard by another frog. So, tailed frogs are silent. The fast water of their habitat also presents a challenge to tailed frog tadpoles. It would be easy for them to be swept away by the water. To prevent this from happening, tailed frog tadpoles have large sucker mouths that they use to attach themselves to the rocks in the streams. Tailed frogs are some of the longest-lived of all amphibians. They can live to be 15–20 years old.
All over the world amphibians are disappearing. Ponds that were once filled with frog song in the spring are now silent and have been so for many years. This was first noticed in the 1980's and is now called the “Declining Amphibian Phenomenon.”
Right now, one third of the world's entire population of amphibians is threatened with extinction. Many species that were once common have become extinct. What is going on?
Amphibians are very sensitive animals. When a habitat is changed, the amphibians are often the first group of animals to disappear. Because they can absorb things through their skin, they are very sensitive to chemicals in the environment. Many chemicals that we use are deadly to amphibians because the chemicals are absorbed through their skin. Some of these chemicals do not kill amphibians right away but instead affect their offspring. Scientists have found frogs with extra toes, arms and legs or without eyes. Often these animals cannot reproduce which then causes their overall population to decline. Scientists are concerned that the amphibians are telling us our environment is not very healthy.
Amphibians play a very important role in their habitats. They are a food base for many other creatures that depend upon amphibians for survival. If amphibians disappear, all these animals will likely disappear as well. Amphibians also eat a tremendous number of animals that we consider pests, especially insects. Some of these insects, like mosquitoes, spread disease. Others eat our food crops. Amphibians are important controls on these insects.