Amphibians are vertebrates that cannot generate their own body heat. They have smooth, slimy, or warty skin and they lay eggs without shells that hatch into an aquatic larval stage (with a few exceptions that do not occur in the U.S.). These tadpoles or larval salamanders grow and most of them change from aquatic, gill-breathing animals to animals that breathe air with lungs. In the U.S., amphibians include frogs, toads, and salamanders. Texas has 70 species of amphibians, according to Dixon’s Amphibians and Reptiles of Texas, 3rd Edition, which was published in 2013.
Frogs & Toads
Toads have relatively dry, warty skin, shorter back legs compared to most frogs, and often live further from water than frogs. Most frogs, on the other hand, have slimy and fairly smooth skin and longer back legs – they can leap where toads only hop.
Both frogs and toads are dependent on water or moisture, and often live either at the water’s edge or in places where there are moist refuges. Although we think of toads living in more dry habitats, we can sometimes see leopard frogs or bullfrogs out on the road at night, wandering some distance from the nearest creek or pond. All frogs and toads are “amphibians,” meaning that they lay gelatinous eggs in the water (with a couple of exceptions in places around the world), start their lives in a water-dwelling form that uses gills to get oxygen, and then metamorphose into a land-dwelling form that breathes air. The eggs hatch into tadpoles that eat plant matter, while the adults eat animals such as insects and other invertebrates.
Amphibian skin is fairly delicate and they can lose water as well as gain water through the skin. In fact, frogs and toads have a “seat patch” of skin that easily absorbs water and is how they drink! Many toxins can easily cross an amphibian’s skin, making many of them particularly sensitive to pollution. (Do not handle them if you have chemicals such as insect repellent on your hands.)
On the other hand, frogs and toads secrete various toxins from their skin, which helps protect them from infections and in some cases may help protect against predators. Most frogs are completely safe to handle, and none will give you warts! However, do not rub your eyes or get your fingers in your mouth after handling them. The skin secretions of toads can result in a burning sensation if it gets in your eyes.
The males of the various species of frogs and toads “call” to females during breeding. This often takes place in the water of ponds and creeks, because when a female approaches a suitable male and they pair up, she will lay eggs in the water. The calls of frogs and toads are a little like bird song, in that different species have different calls and an experienced listener can identify the species by listening to the call. A very good book, with audio recordings of many calls, is The Frogs and Toads of North America, by Lang Elliott and others.
Many frogs and toads are in trouble, in what has been described as an amphibian extinction crisis. Many are disappearing for reasons that include climate change, loss of habitat, and an infection by a particularly nasty fungus that attacks their skin. For more information, see the AmphibiaWeb website.
They may look a little like lizards, but salamanders are not reptiles; they are amphibians. They have skin that may feel rubbery, slimy, or slightly rough, but they do not have scales and they can dry out easily. Like other amphibians, they generally start out as eggs laid in water. Instead of a shell, the egg has a clear membrane through which you can see the embryo developing.
When they hatch, the babies are not like adult salamanders, but are larvae that breathe in the water using gills. This is the salamander version of a tadpole. Later, they generally change into an air-breathing adult form (one group, the lungless salamanders, do not have lungs as adults). Some salamander species live entirely in the larval, aquatic form, and these are called “neotenic” salamanders. Neotenic salamanders are not a different kind of salamander, but the term “neotenic” simply describes the fact that the salamander did not change into an adult, air breathing form.
One group of salamanders, called “sirens,” always remain aquatic and do not develop hind limbs. They are long and eel-like. Another group that is always aquatic and have a long body like an eel are the “amphiumas.” In Texas, we have the “western lesser siren” that is relatively small. In contrast, some amphiumas can reach lengths of over three feet.
Because they depend on healthy wetlands or other habitats that are shrinking because of things like development for human use or drought and climate change, salamanders are in trouble. Like frogs and toads, their skin is porous and they “drink” through their skin. This makes them particularly vulnerable to chemical pollutants in water. Overall, for these and other reasons, amphibians are disappearing in many parts of the world. See organizations such as the Amphibian Survival Alliance for more information.