Judi Manning

Toads and frogs are a great indicator of the environment;
because any disturbance or change in the habitat
affects some part of their life.

Some species could qualify as either toads or frogs. Toads are defined as a group of frog-like amphibians that are usually distinguished from frogs by the roughness of the skin due to a large number of glandular tubercles and shorter hind legs. Thousands of tiny glands keep the frog’s skin moist so they can breathe. This mucous is harmless to humans.

A species selects its living environment based on the temperature, rainfall, and topography that meets its requirements. Each species requires a different mix to survive so toads and frogs reside in most parts of the world, except Antarctica, the driest deserts, and many oceanic islands. The largest number of species is found in moist, tropical areas. Few are found in large bodies of water because few are totally aquatic. Swamps and marshes contain the right "mix" for many species.

Most toads and frogs have a well-defined territory. Those that eat at night do so in a limited area and have a customary hiding place. The "yard" toad has adapted to human areas and is not found far from that location.

Both frogs and toads are carnivorous and swallow their food whole. Frogs use their teeth. The terrestrial frogs and toads capture food by flicking out their mucous-coated tongue which is attached in the front of the mouth of most species and is drawn back in the mouth. "All anurans blink when they swallow and because no bone exists between the eye and the mouth, the eye is pushed against the roof of the mouth, forcing the food further back". (Encarta). If the captured food is too large or attempting to escape, they will use their hands to cram it into their mouth. Aquatic frogs sense movement in the water by their finger-tips and scoop the prey towards their mouth with their front limbs.

Most terrestrial frogs and toads eat ants, termites, beetles, slugs, snails, earthworms, and other small living invertebrates, which helps control the insect population. Some of the larger species eat small vertebrates, such as rodents, fledgling birds, young snakes and other species of toads and frogs. The larger aquatic species of frogs eat fish they catch and swallow underwater. The smaller species eat aquatic invertebrates such as insect larvae and crustaceans.

Neither frogs nor toads drink. Their total body weight includes 80% water which is absorbed through their skin by osmosis. The amount of water retained in the bodies of aquatic species must be limited. The amount of water passing out of the bodies of terrestrial species must be limited.

All amphibians rely on outside heat sources to warm them up. They function best from 68 to 77 °F. In Michigan, frogs hibernate when cooler temperatures arrive. In the dessert areas, they are more active during the cooler times of the year and burrow to keep cool when the temperatures rise.

Their breeding behavior can be categorized as (1) seasonal or cyclic breeders, (2) opportunist breeders, or (3) continuous breeders. Each male selects and defends his territory prior to breeding season. The male’s call of each species is distinct so the species do not interbreed. They begin calling from late winter to early summer from their breeding sites. The loud vocal sound is produced as air is forced over the voice box and the vocal cords. The smaller the frog, the higher pitched the calls. The frog that calls the longest, loudest and/or more elaborate is the winner.

All 3,500 species of toads and frogs differ slightly in their appearance. The ability of these animals to adapt to changing conditions has resulted in the large diversity in their size, shape and color. Those that must depend upon their ability to leap, have long, powerful legs. Those that do not need to perform large leaps to survive, have shorter legs. Those that swim, are more streamlined in shape, have large webbed feet. The land types are rounder and have more webbing.

There are field guides to aid in the identification of frogs and toads but up-close detective work is needed to identify them. Some identifying characteristics are pupil shape, amount of webbing between the digits, the presence or absence of enlarged glands, toe-pads, etc. (Toads & Frogs, Pg. 14) Identification of tadpoles is more difficult.

Toads and frogs have many enemies/predators: storks, herons, larger of their own species, large invertebrates, spiders, fish, turtles, small mammals like shrews, mustelides, raccoons and larger animals. For survival frogs and toads are very secretive. They rely heavily on their camouflage and remain still until the last possible moment of escape. Some species play dead.

TADPOLES The growth rate of a tadpole depends on its environment. Most tadpoles eat algae and bacteria and become frogs in two to three months. Those living in a temporary pool of water develop quickly (within two weeks - Scaphiopus - spade foot toad). Those living in a cool, mountain stream can take up to three years to develop (Ascaphus truei in No. America).

Tadpoles are food for aquatic insects, nymphs, fish, newts, and other larvae. Only a few of the large number of eggs that are laid survive.

TOADS are shy, usually nocturnal, hide in dark, damp places by day and hop around at night searching for insects, grubs, slugs, worms, and other invertebrates. Toads are often brownish or grayish with warty skin, flat head, swollen parotial glands on the sides of the neck behind their eyes, bright, jewel-like eyes with a transverse pupil, and slightly webbed toes, stouter then frogs and can’t leap as far.

Both sexes of toads are basically the same color, except in the genus Bufo. In the species Bufo pereglenes the sharpest contrast exists. The male is a uniform golden orange; the female is a deep red with large brown blotches. The African Hyperolius hieroglyphicus male is black with yellow reticulations. The female is bright green with yellow dorsolateral stripes. It is believed the bright colors help the male find the female in the dark cloud forests.

Our toads hibernate in burrows. They mate in the spring and lay lots of ova in pools in gelatinous strings four feet in length. The tadpoles are smaller and darker than frogs and do not transform into terrestrial toads until autumn.

One toad genus, Bufo of the family Bufonidae, includes 200 species. These species are most abundant in the tropics, but are native to most areas of the world, except Greenland, Australia, New Guinea and New Zealand.

The largest toad species is the giant toad (Bufo marinus), which is about 8" in length. In an effort to control beetles and other pests, in the early 19^th Century, toadlets of this species were introduced in Hawaii and in 1935 to Australia where no toads existed. These toads spawn up to 30,000 eggs at one time and have become a pest. They also eat native wildlife which upsets the delicate balance of nature. Other countries learned from this mistake and the introduction of this toad in some places is outlawed. Some countries have banned exportation of frogs. Those that are protected are Bufo houstonensis in the US, Bufo calamita in Great Britain, Bufo pereglenes in Costa Rica and three species of Leiopelma in New Zealand.

Some toads and frogs get transplanted when their "homes" (hiding places) go cross country. The males, because of their calls, are easy to catch, become pets. Some escape or are released in a new environment. Many frogs are killed on the roads when they try to cross them to get to their breeding ground.

FROGS shed their outermost, dead (epidermis) layer of skin every few days. The frog pulls the skin away from its body with its mouth and swallows it as it pulls. Frogs absorb oxygen through their skin either in or out of the water, but the skin must be moist in order for this to occur. Air is pumped through their lungs by the raising and lowering of the floor of the mouth.

One or two jumps with their long, powerful legs takes them away from danger. Aquatic frogs never stray more than a leap away from the pond to escape predators by hiding in the mud or debris at the bottom or continue jumping to the other side. If some are not quick enough, they will secret a lethal mucus coating known as batrachotoxins. A high concentration is lethal. The most deadly toxins are found in 55 known species of Central and South American poison dart frogs. The bat, Trachops cirrhosis, from Central America is a specialized predator of various species of poisonous frogs and locate the male from its mating call. Some species have prominent eye spots to deter predators; some scream when approached or grasped. Some species of frogs have a "flash" marking. This marking is a brightly marked patch of skin that is exposed when they straighten their legs and jump. This bright spot attracts the predator’s eye and confuses them because it is gone when the frog lands. The predator then looks for the bright color and cannot find the frog. There is another species that opens its mouth, screams loudly and lunges at the tormentor, biting hard and holding on, leaving a painful impression of its lower tusks.

There are a number of parasites that live in various parts of frog species to which the frogs seem resistant. The reproduction of the parasites is timed to the reproduction of the frogs. The parasites eggs pass through when the frog lays its eggs.

Tadpoles have adapted to their environment as well. Frog tadpoles that live in ponds and quiet water have plump bodies and high fins. Those that live in rivers and streams are more streamlined and have long tails and low fins. There are many differences among the species that are explained in Frogs & Toads of the World. Tadpoles breath with gills.

The largest frog is the Goliath frog found in West Africa. It measures 300 mm in length. The length of a frog is measured from the tip of its nose to its vent. In North America, the largest frog, the Bufo alvarius, found in the Colorado River, is 150 cm. The female is usually larger than the male. Several Eleutherodactylus species of frogs are slightly more than 10 mm. This small frog produces one egg at a time. Psyllophryne didactyla, from Brazil, only 9.8 mm and is the smallest frog.

Most frogs are nocturnal and their eyes close down to a slit in bright light. The ears are just behind the eyes. Most frogs are dull gray or brown. However, some are brightly marked to:

1. help them to blend into their environment; 
2. warn predators they are poisonous or have a bad taste; 
3. help it to absorb or reflect heat; 
4. identify itself in order to establish a territory;
5. attract a mate.

The color is produced by either pigments throughout the upper layer of skin or between it and the upper layer of skin. Others have specialized cells that contain a different type of pigment that reflects light. The movement of the pigment is affected by temperature and humidity: warmth and dryness make it pale; cold and dampness make it bright. Some species of frogs have two or more color phases (polymorphism [striped, speckled and plain]) These frogs may exist side by side. This is believed to aid in their survival. A predator will become accustomed to searching for a particular look and overlook one of another pattern. Males and females are similar in color. They use a call to identify their gender.

The tree frog has special expanded disks that help it climb. The hairy frog (Astylosternus robustus) is the most unusual frog. During breeding season, it has hair like skin projections that develop on the male’s body and legs.

The earliest frog-like fossil, Triadobatoachus, is 10 cm long, has a wide, flat skull and a short tail. It was either aquatic or a metamorphosing tadpole and was found in deposits from the Triassic period, 220 - 230 million years ago in Madagascar. There is a gap of 50 - 60 million years before the next frog fossil appears. (Toads & Frogs, Pg. 16)

Frogs have been involved in legends and folklore dating back before 1000 BC. During the Middle Ages, they took on more sinister roles in Europe as they became associated with evil and witchcraft. Frog legs are eaten in many parts of the world. They are also used in education, research, and medical labs because the skeletal, muscular, digestive, nervous and other systems are similar to higher animals.

More information on malformed frogs

References

1. Encarta, Toads
2. Toads & Frogs of the World, Christopher Mattison, 1987
3. Nongame Wildlife Species & Resources, http://www.dnr.state.mi.us/wildlife/Heritage/frogs/default.htm
4. Nongame Wildlife Species & Resources, http://www.dnr.state.mi.us/wildlife/Heritage/frogs/

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