| ||Frog |
| ||Skin smooth, moist||Skin dry, warty-looking|
| ||Slender body||Heavier body|
| || Usually lives near water ||May live far away from water |
| ||Visible eardrums||Visible eardrums|
| ||No parotid glands||Visible parotid glands|
| ||Tree frogs have toe pads||No toe pads|
Note: There are a few visual differences between frogs and toads, as you can see above, but there is no scientific distinction between them physiologically. Toads are simply frogs belonging to a different family. So, in this article “frog” also applies to “toad,” in the same way that robins and orioles are both birds. We’ve highlighted in red any noteworthy physical or behavioral differences between them.
Frogs and toads are invaluable members of a backyard wildlife habitat as predators of insects, spiders, worms and slugs. Reportedly a single toad will eat about 10,000 insects over the summer. Some large toads and frogs even eat tiny rodents or reptiles.
Frogs and toads are amphibians, animals that spend part of their lives on land and part in the water. There are more than 5,000 described amphibians worldwide and frogs and toads make up 90 percent of them. Along with newts, salamanders and caecilians, they’re in the order Anura (uh-NOO-ruh), a word from Greek for “tail-less.” Anura is divided into many different families, including one for True Frogs (Ranidae) and another for True Toads (Bufonidae). Ranidae has about 400 species and Bufonidae contains about 300 species. Species in these two families may be the ones you most often notice in your yard, but there are also tree frogs, Spadefoot Toads and Narrow-mouthed Toads, among others. The word “frog” evolved from Middle English frogge.
Frog fossil. (Keith Schengili-Roberts; cc by 2.0)
Amphibians evolved from fish that moved out of the water onto land about 400 million years ago (they still spent most of their time in water.) Frog- and salamander-like animals date back as far as 290 million years. The earliest modern frog, one containing all the frog features of today, showed up about 125 million years ago. In 2008, scientists in Madagascar discovered a toad-like fossil that’s 70 million years old. They named him Beelzebufo, or Devil Toad, because of his size: 10 pounds and 16 inches long!
Most frog species live in tropical rainforests, but they’re native to everywhere there’s a suitable habitat, except Antarctica and some islands. Some toads live in arid areas, burying themselves during dry spells and emerging when it rains. Frogs (as well as other amphibians) are threatened around the world from loss of habitat. Other forces are at play, too, such as chemical pollution of air and water, disease and over-harvesting for food. Many may become extinct in the near future; in some areas of the world certain species are already gone.
In the U.S, the smallest frog is the Little Grass Frog (Limnaoedus ocularis) which, at a mere 3/4-inch, fits on a penny. The largest U.S. frog is one you might guess: the American Bullfrog (Rana catesbeiana), who’s almost 8 inches in diameter and can weigh more than 1-1/2 pounds. The smallest toad in the U.S. is the Oak Toad (Bufo quercicus) who measures 3/4 to 1-1/4 inches.
Smaller than an M&M, the world’s smallest frog, Paedophryne dekot. (Fred Kraus / Wiki; cc by 3.0)
In the world, the largest frog is an endangered African species, suitably name the Goliath Frog (Conraua goliath
), whose body can be more than a foot long. With its legs extended, it stretches to more than 2-1/2 feet. A Cuban frog called the Monte Iberia Eleuth (Eleutherodactylus iberi)
, and the Brazilian Gold Frog (Brachycephalus didactylus
) are the world’s smallest, with the former a fraction smaller than the other at 9.6 millimeters vs. 9.8 millimeters (3/8-inch). The smallest frog in the world is also the world’s smallest vertebrate (animal with a backbone) with four legs. Discovered in Papua New Guinea in 2010, Paedophryne dekot
measures only 8.5 to 9 millimeters long — that’s this long: ……….
There are a few visible distinctions between frogs and toads. Once you know them, it’s easy to distinguish between the two: Frogs have moist, smooth skin; a slender body; visible eardrums on the sides of their head; no parotid glands; and tree frogs have toe pads. Toads have dry, warty-looking skin, a heavier body; visible eardrums; visible parotid glands; and no toe pads.
Frogs have a flat, wide head, with big, bulging eyes at the top. Frogs (not toads), which spend much of their time in the water, can sit motionless with only the top of their head above water — convenient for catching unsuspecting insects. (Toads spend most of their time on land.) Their eyes have an amazing function beyond vision — they also help in swallowing: When a frog catches prey, its eyes close, drop down into the roof of the mouth and help push the food down the throat!
Leopard frog. (Pdunant / Wiki; cc by 3.0)
Frogs have excellent vision in both daytime and night, with a wide field of view that allows them to see to the front, sides and partially behind. They lack a neck, which leaves them unable to turn their head or move it up and down, so their wide vision is important for spotting predators. The upper and lower eyelids are underdeveloped and move very little. In order to completely close their eyes, frogs must draw their eyeballs deep into their sockets, which pulls the eyelids together. They also are able to move a transparent membrane up over their eyes, which protects and cleans them.
Their nose sits on top of their head and they have a good sense of smell. They hear through an external ear on each side of their head. The ears are large, circular membranes called a tympanum, or eardrum. There’s a muscular membrane at the end of the inner ear that’s thought to help protect their ears from extremely loud noises — which they produce themselves: Some frogs have calls that are so loud they can be heard a mile away. In 2008, scientists discovered a species of frogs living near a noisy area in China that can tune their hearing to different frequencies, like a radio knob, effectively tuning out objectionable noises or even the calls of other frog species.
Most, but not all, frogs have teeth, although very short ones. They’re located on the upper jaw only and used for grinding food. Toads don’t have teeth; they swallow their food whole.
Frogs have a mucus gland in their mouth that produces a sticky substance that coats their tongue. Their tongue is long and the base of it is fastened at the front of their mouth rather than at the back. This allows them to hold the tongue folded with the tip of the tongue facing the throat. When an insect happens by, the tongue can be flicked out quickly and accurately. The mucus helps to “glue” the insect to the tongue. Some frogs lack a tongue and use their fingers to catch prey and place it in their mouth.
Frogs breathe in an unusual way. Called buccal pumping, it’s a “two-stroke” process: When they lower the floor of their mouth, it draws air in through their nostrils and pulls air from their lungs into their buccal (mouth) cavity. When they raise the floor of their mouth, it does the opposite, pushing air out, as well as into the lungs.
How buccal pumping works. (Mokele / Wiki; cc by-sa 3.0)
Frogs have two arms and two legs that are pretty similar to those of humans: Their arms have a humerus, fused radius and ulna bones and four fingers. Their legs have a femur, fused tibia and fibula bones and five toes. The shoulder blades and collarbone are shaped similar to a human’s, too.
American Bullfrog. (Ryan Somma / Wiki; cc by-sa 2.0)
Frogs that spend a lot of time in water have longer hind legs than more terrestrial species. Also, their feet have more webbing, which aids in paddling through water. By comparison, the webbing on the feet of tree frogs, which spend all their time on land, covers only a half or less of the length of their toes. The toes of tree frogs differ in another way, too: They have mucus-tipped, bristly pads on their toes that help them stick horizontally or even hang from the underside of leaves.
There’s an unusual group of frogs, called Chinese gliding frogs, that stretch their toes wide and the webbing serves as wings, allowing them to glide from high places to lower places. They “fly” from tree to tree in this manner. “Spadefoot” toads, who live in dry habitats, have claw-like growths on their hind feet which they use for digging burrows. Their method of execution is interesting: as they dig, they move backwards in a circle until the burrow is deep enough for them to disappear into it.
Some species of frogs (and toads
) walk like a lizard (watch walking toad here
). But most hop as a standard method of locomotion on land, and they’re powerful jumpers. The record for the longest frog jump in the U.S. — 7.2 feet in a single bound — was set by an American Bullfrog, cleverly named Rosie the Ribeter, at the Calavaras County (California) Fair in 1986. The African Tree Frog reportedly can jump 14 feet. The arms of frogs, which are shorter, are of little use in jumping, but they help to cushion the landing. Their long jump owes it all to long, powerful hind legs with muscles and tendons that perform like springs. How frogs jump so high.
Skin and coloration
Frogs usually have thin, smooth skin. Toads usually have dry, bumpy skin, but not always. Some frogs have spines or tubercles that camouflage them so well they look like moss or lichen. Most frogs have dull coloration — browns, greens, grays — to help camouflage them in their environment.
Note the round toe pads on this
Red-eyed Tree Frog (Agalychnis
callidryas; native to C. Amer.)
(Carey James Balboa/ Wiki)
Some frogs become paler or darker in response to certain stimuli and many change their color altogether. The changes occur because of star-shaped pigment cells in the skin, called chromatophores. Different chromatophores contain different granules of color: some cells have red, some have yellow, some have black, and so on. How the changes occur is complicated, but they’re triggered by a number of different variables: excitement, humidity, light, temperature or surroundings.
The Pacific Tree Frog (Hyla cinerea), for example, changes skin color to match the color of the background, moving from shades of light-green to dark-brown as the need arises. Gray Tree Frogs can be even more dramatic. Their normal coloration varies, with some being yellow and others green, gray or brown. But some are almost black and can change their color to nearly white. There’s a small African frog who is creamy-white and lives in the white blossoms of a particular lily. When the flowers die and turn brown, it turns brown, too.
The outer skin (epidermis) of frogs is moist. The moisture comes from mucus that’s secreted by glands in the lower layer of skin (dermis). The skin of true toads secretes moisture, too, and they’re able to retain it longer. Still, their skin is drier than that of frogs, allowing them to live farther from water. Some toads even live in arid habitats, where they dig burrows to escape skin-drying conditions.
The moist skin of frogs does more than cover tissue and bone. Although frogs have lungs and take in air through their nostrils and mouth, they absorb additional oxygen through pores in their skin directly into their bloodstream. This is a process called cutaneous gas exchange. This is especially true when they’re underwater, where 100 percent of their oxygen intake is through the skin.
Frogs also “drink” through their skin rather than with their mouth. (It’s this permeability that makes frogs so victimized by pollutants — their skin offers them little protection.) Frogs shed (molt) their skin about once a week. They loosen old skin by twisting their body all around. Then they pull their skin off over their head in one piece, like a sweater. They don’t leave their old skin laying about, like dirty clothes; they eat it.
Toads and their ‘warts’
The large, puffy bump behind this toad’s eye is a parotoid gland. (© Ryan Vinson)
Toads (and some frogs, too) have warty-looking bumps all over their body, but they aren’t warts and they don’t cause humans to get warts by touching them, a common myth.
The ‘warts” are a mix of two types of glands: mucous glands, which can sometimes be poisonous; and granular glands, which produce a much more toxic substance, called bufotoxin. Bufotoxin is secreted through two puffy glands. There’s one behind each eye and they’re easy to see. Their milky-looking poison is released when a toad is squeezed or shaken (as dogs often do). It can kill small predators and in some rare instances has killed small dogs.
Bufotoxin reacts with the mucus lining of a predator’s mouth and tongue and often causes foaming of the mouth, making the animal look rabid. It’s a toad’s only defense against predators — it’s temporary, but effective. It’s very bitter, prompting most animals to drop the toad immediately, and most will never again try to taste a toad.
Congo Tree Frog (Hyperolius viridiflavus). (Nick Hobgood / Wiki cc by-sa 3.0
Bufotoxin doesn’t typically affect human skin, but taken internally it can affect the heart, cause hallucinations and act as a vasoconstrictor. If you handle a toad, don’t squeeze it, and keep your hands away from your eyes, mucous membranes and any open wounds, until you’ve washed up. See our FAQ page
for first aid tips for pets.
In the tropics live some of the most eye-catching animals on earth: brightly colored frogs dressed in vivid yellows, blues, reds, oranges and purple, some with lovely patterns of spots or stripes. These beauties have much to visually admire, but they can’t be touched. Their noticeable coloration serves as a warning to stay away. Toxic frogs tend to be diurnal (active in daytime) because they don’t fear being seen.
There are no frogs or toads in the U.S. that can be lethal to humans, unless ingested. Even the infamous Cane Toad (Rhinella marina) of the southern U.S. can be handled safely, if done with care. The most poisonous animal on earth is probably the Golden Poison Frog from Central and South America: Just one milligram of its poison can kill up to 20 people.
Communication: Frogs communicate with others of their species. Their calls fall into categories of attraction calls and aggression calls, as well as release calls, which are used by both males and females to signal non-readiness to mate.Some frogs emit their attraction calls separately and others join a group in an immensely loud “chorus” of calls. For some frogs, making a call inflates and pulsates a conspicuous vocal sac located on their throat.
Green Tree Frog with inflated vocal sac.
(© Phil Morley, Clearview Images)
We’re all pretty familiar with the deep croak of Bullfrogs, but frog calls also include chirps, trills, twitters, peeps, clicks, twangs and other sounds that defy description. In order to attract the right mate, each species has its own special call. As for the frog that goes, “ribbit, ribbit, ribbit,” it’s the Pacific Tree Frog (Pseudacris regilla). Listen here.
Defenses: Frogs have few defenses, so most are active at night when they’re harder to see. Camouflage coloration allows them to sometimes hide in plain sight. Some change color to match their background. Many play dead when approached by a predator, relying on most predators’ preference for live food. Some frogs hop away, others may dive into the water. Some puff up to appear bigger. Watch toad playing dead
Estivation: In summer and in warmer climates, frogs become inactive when weather conditions are too dry or too cold. They burrow into mud or sand, or enter cracks or holes in logs and rocks, while some may hide under leaf litter or in abandoned burrows. They go into a dormant state known as aestivation, which differs from hibernation in that it’s a shallower “sleep.” Some species develop a hard “cocoon” that locks in moisture.
Hibernation: Frogs that live in temperate areas dig down into the soil or move into such places as caverns, abandoned burrows, a crevice in a log, under a rock, under leaf litter or debris, anywhere they think they’ll be safe through the winter. They hibernate there, some of them up to eight long months. Aquatic frogs hibernate underwater, partially burying themselves in the soil at the bottom. They may occasionally swim slowly around. Since frogs are cold-blooded animals, their body temperature drops to the temperature around them, which will hopefully remain above freezing. If they freeze, they die.
There are five known exceptions to this in North America: the Wood Frog (Lithobates sylvaticus), Cope’s Gray Tree Frog (Hyla chrysoscelis), Eastern Gray Tree Frog (Hyla versicolor), Spring Peeper (Pseudacris crucifer) and Western Chorus Frog (Pseudacris triseriata). These frogs can withstand freezing. Ice crystals may form under their skin, in their bladder and elsewhere. Their heart, respiration and muscle action stops. And yet they don’t die. When freezing begins to occur, their body produces, through a series of actions, a high glucose concentration that acts like antifreeze. When their body warms up, the ice melts, the organs spring into action!
All frogs live close to ponds, lakes and streams. Tree frogs spend most of their time in trees or tall vegetation, while other frogs may be seen on the ground or in water. Toads are willing to move farther from water.
Frogs are considered bio-indicators because their disappearance in an area indicates that something unhealthy is going on in the environment. When their populations decline, something has gone amiss. Their permeable skin absorbs toxins easily while in water and on land. When they start dying off, or develop mutations, scientists take note. Broadly speaking, where frogs are safe, humans are safe.
All frogs move to water in mating season. Most male frogs become sexually mature at around 10 to 12 months of age. Females are usually sexually mature at two to three years. Male frogs start calling for females in spring. Each species has a specific call. Females come to the callers, choosing a mate based on call and, possibly, appearance. Usually they couple in the water, but depending on the species it may occur in trees above water or on the ground. The male climbs on the female’s back and wraps his forelegs around her “waist,” neck or head in an embrace called amplexus. It doesn’t involve copulation, but rather pseudocopulation: There’s no contact of sexual organs between the two. Instead, the male releases semen onto eggs as they leave the female’s body.
Frog eggs are subject to extreme predation. So, they’re usually laid in huge batches of thousands of eggs (sometimes called “frogspawn.) This increases the chance that a few will survive. When the eggs touch water, even if it’s just a tiny puddle in a cupped leaf, they soak it up and swell into gelatinous masses. Toads lay their eggs in a long strand.
Mass of frog eggs. The black “dots” are developing tadpoles. (© Maurice van der Velden / iStock)
Some frog parents watch over their eggs. Some males carry eggs from a moist place, such as the water in a cupped leaf, to a wetter place, like a pond. They may do this by placing the eggs on their back, in a pouch on their belly or even in their mouth. Some males wait for the eggs to hatch and then transport tadpoles.
The time it takes for eggs to hatch varies from two to 40 days — the warmer the temperature, the shorter the time. Frogs hatch as tadpoles. This stage may last for days, weeks or years. The Bullfrog, for example, hatches in a few days and spends about three years as a tadpole (also called pollywogs or froglets).
Green frog life cycle. (LadyofHats / Wiki; PD)
Through the course of this stage, tadpoles make their change into frogs (called metamorphosis). They eat voraciously, first on algae and later on tiny water animals, small fish and insects. Their appearance is quite different from their parents.
At first, tadpoles have an oval-shaped body with gills, a long tail and, like their parents, large eyes. Body parts begin to develop: their tongue, teeth, certain bones, kidneys, glands and gonads. Their legs begin to grow and finally the tail is absorbed. The gills are absorbed, too, as the lungs develop. Tadpoles move through water the same way fish do. After metamorphosis, frogs leave the water for a more terrestrial life or continue their water lifestyle, depending on the species.
Frogs are carnivores. They eat insects, spiders, snails, worms, small fish and small land animals, such as mice. A frog hunts by sitting motionless, rarely even blinking. When prey walks or flies by, his mouth opens and his tongue flicks out and back, faster than we can see.
Captive frogs are known to live 15 to 20 years, but it isn’t known just how long frogs live in the wild because they’re hard to track. Some are known to have lived at least five years, but most are probably eaten by predators within days of leaving the water.
Humans are the biggest threat to frogs as a result of habitat destruction, pollution and pesticide use. Also, many people eat them and millions are used in scientific research or classroom experiments. Some are captured and kept as pets. Other predators are snakes, lizards, large spiders, fish, birds and foxes and other mammals. Automobiles also kill many frogs in spring and fall as they cross roads while migrating between shallow, summer breeding ponds and deeper ponds for hibernating.
Top photo: Liz West / Flickr; cc by 2.0