About Amphibians

What is an amphibian?

The word “amphibian” comes from the ancient Greek words amphi, which mean “both” or “double”, and bio, which means “life.” This name alludes to the two life stages that are typical of amphibians: an immature aquatic stage (tadpole or larvae) which metamorphoses into a terrestrial adult. However, this is not always the case, as some species metamorphose into an aquatic adult and remain in the water throughout their lives, while others (e.g., Eastern and Western Red-backed Salamanders) lay their eggs on land and do not have an aquatic larval stage. Biologists divide class Amphibia into three major groups: frogs and toads (order Anura), salamanders (order Caudata), and the limbless caecilians (order Gymnophiona), which are found only in the tropics.

Like mammals, birds, reptiles and fish, amphibians are vertebrates (animals with a spinal column). Amphibians generally have moist, permeable, glandular skin, although the skin of some highly terrestrial species, such as toads, is drier and less permeable. Most species have lungs or gills, but they can also absorb oxygen by diffusion through their skin. Some, such as the plethodontid salamanders, lack lungs and gills altogether as adults and rely entirely on their skin for respiration. Many amphibians also have poison glands (e.g., the large parotid glands on toads), which provide protection from predators. Some species, such as the Eastern Newt, also boast bright colouration to warn predators that they are toxic. Although many of Canada’s amphibians contain toxins that help deter predators, they are not dangerous to humans unless consumed. Amphibians are ectothermic (commonly referred to as cold-blooded), which means they do not generate their own body heat, but rather, their internal body temperature depends on the surrounding environment. Unlike reptiles, amphibian eggs lack protective shells and must be laid in water or damp environments to prevent them from drying out. In terms of physical appearance, amphibians are most easily differentiated from reptiles by the lack of scales and claws.

Amphibian Diversity in Canada

As of August 2018, there are 7,910 known species of amphibians: 6,985 frogs and toads, 716 newts and salamanders, and 209 caecilians (AmphibiaWeb 2018), with new species discovered each year. Despite its northern latitude and cool climate, amphibians occur throughout most of Canada, and some species extend into the northern reaches of the Yukon and Northwest Territories (the Wood Frog is even found within the Arctic Circle!). Canada has 23 extant species of salamanders and newts and 25 extant species of frogs and toads. Some species, such as the Long-toed Salamanders, are further broken into multiple subspecies across Canada, which are not reflected in these numbers.

Ecology and behaviour

Since amphibians are ectothermic, they have to regulate their body temperature by moving between warmer and cooler environments. Most amphibians are also susceptible to rapid water loss due to their porous skin, and they have to remain moist to avoid dehydration. For these reasons, amphibian behaviour and activity is largely dictated by environmental conditions. Because metabolic activity and energy levels are dependent on temperature, amphibians are relatively slow and inactive when they are cold and more active when they are warm. Terrestrial activity tends to be highest during rainy weather, which allows amphibians to remain moist while they forage or migrate across the landscape. Terrestrial amphibians avoid desiccation during periods of hot, dry weather by seeking shelter under cover, underground or in other moist micro-environments. By not expending metabolic energy to maintain a particular body temperature, ectotherms have much lower energy requirements and require much less food than similarly sized endotherms (warm-blooded animals).

Most of Canada’s amphibians avoid freezing temperatures during the winter by hibernating underground below the frost line (in mammal burrows, tree root hollows, rock crevices or other cavities), and at the bottom of rivers, lakes or wetlands, beneath the ice. Since their body temperature drops to that of the surrounding environment, which is often as low as 1 or 2°C in the hibernation site, metabolic rate slows dramatically, allowing them to survive for months with no food and very little oxygen. Individuals that hibernate underwater are able to obtain what little oxygen they do require through their skin and the lining of the mouth and throat. Some species (e.g., Gray Treefrogs, Spring Peepers, Western Chorus Frogs, and Wood Frogs) are able to survive freezing temperatures during hibernation by increasing the levels of glucose in their blood, which lowers the freezing point of tissue and also prevents the formation of ice particles within cells as they freeze. Remarkably, these individuals can survive being frozen for prolonged periods of days to weeks. Many aquatic species, particularly stream salamanders and Mudpuppies, remain active under the ice during the winter.

Where do they live?

Amphibians occupy a wide-range of habitats in Canada, but unlike reptiles, most are found in or near water or in other moist habitats (e.g., damp forest floor) where they are not at risk of drying out. Groups like toads, spadefoots and some salamanders have thicker, less-permeable skin and can be found in drier habitats than most other amphibian species. Some of Canada’s amphibians are highly aquatic and live year-round in and around permanent bodies of water, such as lakes, wetlands and streams. For example, Green Frogs and American Bullfrogs inhabit lakes and wetlands, while several species of stream salamander are found in and around small, fast-flowing streams. Other species, such as tree frogs, toads and salamanders of the genus Ambystoma, spend much of the summer foraging in forests, meadows or other terrestrial habitats, but always return to water in the spring to breed. Some amphibian species have completely cut ties with their aquatic habitats, spending their entire lives on land. For example, some of Canada’s plethodontid salamanders live year-round in the cool, moist understory of forested habitats. Amphibians can also be arboreal, meaning that they can be found in the forest canopy. Tree frogs have adhesive toe pads that help them climb high up into the trees. There is even one salamander species — the Wandering Salamander — that lives and lays its eggs in the forest canopy in the damp coastal forests of BC!


Almost all of Canada’s amphibians lay their eggs in water, such as lakes, rivers, streams and wetlands. However, a few species lay eggs on land in damp or humid environments, such as under rotten logs in the forest understory. Most amphibian species breed in the spring, but some breed during the fall, while others may breed throughout the spring, summer and fall. Frogs and toads have species-specific calls that the males use to attract females during the breeding season. All but two of Canada’s frogs have external fertilization, meaning that the female’s eggs are fertilized by a male after they are deposited in the water. Males of the tailed frogs of the genus Ascaphus have an extension of the cloaca (referred to as a “tail”) that allows for internal fertilization — an adaptation to the fast-flowing streams that these species inhabit. Most salamanders have internal fertilization, but without direct copulation; male salamanders deposit a sperm packet called a spermatophore, which the female picks up with her vent and uses to fertilize her eggs internally. Although direct copulation does not occur, the exchange of the spermatophore often involves elaborate courtship behaviour. The eggs of most amphibian species hatch into aquatic larvae (commonly called “tadpoles” or “pollywogs” for frogs and toads), which breathe through gills. After a few weeks to a few years, depending on the species, the larvae undergo metamorphosis, transforming into adults. The adults of many species disperse onto land for at least part of the year and breathe air through their lungs or skin rather than gills. However, some species (e.g., Mudpuppy) are neotenic, meaning that sexually mature adults retain larval characteristics, including gills, and remain in aquatic habitats for life. Conversely, fully terrestrial species that lay their eggs on land do not have an aquatic larval stage (e.g., Eastern and Western Red-backed Salamanders); instead, the eggs hatch into miniature versions of the terrestrial adults.

What do they eat?

All of Canada’s amphibians are carnivorous as adults, consuming insects, slugs, spiders, worms, and other invertebrates. Larger species, particularly American Bullfrogs and larger salamanders may consume vertebrates like fish, snakes, other amphibians, mice and even small birds. Amphibians hunt primarily by sight, and most species actively forage for their prey. Frogs and most salamanders have muscular, sticky tongues that they extend to capture their prey, while aquatic salamanders (and the tropical caecilians) capture prey by grabbing it with their mouths. Most amphibians have very small teeth, but these are used primarily for holding and subduing their prey, which are typically swallowed whole. Salamander larvae have teeth and are carnivorous, preying on small invertebrates, zooplankton and sometimes even other salamander larvae. Most frog tadpoles are either filter feeders, consuming bacteria, detritus and other organic matter in the water or they have beaks or rows of teeth that are used to scrape algae and other materials off rocks and other surfaces. However, tadpoles of some species, such as spadefoots, can develop large beaks and strong jaws under certain conditions that they use to hunt larger prey, including other larvae.