Missouri forests, prairies, rivers, swamps and marshes are home to a multitude of toads and frogs, but few people know how many varieties we have, how to tell them apart, or much about their natural history.
The toads and frogs native to Missouri are a valuable part of our outdoor heritage. Most people probably don't give them much thought, but we need these amphibians to control destructive insects and to add their voices to the sounds of spring and summer nights. Just hearing or seeing them adds to our enjoyment of outdoor Missouri.
Their role in nature can be illustrated by the huge number of insects they eat and by the number of animals that eat them or their tadpoles. Since their bodies readily take in contaminants, they are good indicators of environment health. Amphibian skin secretions also are used in medical research to control and cure human diseases. And a discussion of the value of frogs should include the fact that thousands of bullfrogs are harvested in our state each year for human consumption — one of Missouri’s truly gourmet outdoor foods.
All Missouri toads and frogs must return to a body of water to reproduce. Most species breed during the late winter, spring or early summer, but southern leopard frogs, Rana sphenocephala, are also known to breed during rainy periods in the autumn. The majority of these amphibians select fishless bodies of water for breeding. Flooded fields, ditches, woodland and prairie ponds, and temporary pools are favorite breeding places. A few adventurous males locate an appropriate breeding pond when the temperature and humidity are suitable and begin to call. Each species of toad or frog has a distinct breeding call that entices females to join them and select a mate. Soon, other males congregate and add their voices to the chorus. Females, heavy with eggs, enter the pond and are grasped by a male in an embrace called “amplexus” and begin the process of egg-laying. During egg-laying, the male’s vent opening is positioned just above the female’s vent, and as her eggs are released, the male fertilizes them with his milt. He will retain his firm grip on her until all the eggs have been laid.
Most eggs hatch within 10 to 14 days of being laid, but they may hatch much sooner if the water temperature is above 70 degrees F. The tiny, newly hatched tadpoles rest for a few days by clinging to aquatic plants, receiving nourishment from the last of the yolk sac stored in their bellies. Most Missouri tadpoles eat aquatic plants — especially algae — as they develop in the wetland. Tadpoles have gills, somewhat like fishes' gills, which are covered and protected by a flap of skin. As development progresses, the hind legs form and enlarge. The tail begins to shrink at this stage. As the front legs appear, the tail continues to become smaller. Soon the gills are not used and the late-stage tadpole begins to breathe air at the surface, using brand-new lungs. The final stage of development from a tadpole to a young frog, known as a froglet, is the combination of the disappearance of the tail and the change from a life underwater to a life on land or along the edge of a pond or swamp. Soon after transforming from tadpoles to froglets or toadlets, these young amphibians begin eating insects, small spiders and worms. They grow quickly.
Toads and frogs defend themselves in several ways. Most of their predators are fish, turtles, snakes, birds and carnivorous mammals — shrews, mink, skunks, and raccoons. Missouri’s larger species of frogs also will eat other frogs.
Toads cannot jump as fast as frogs. To escape a predator, toads defend themselves by producing toxic or unpleasant-tasting skin secretions that are released when the animal is seized. Due to their toxic skin, toads are not a popular food among most predators. Even their eggs and tadpoles are said to be toxic.
Frogs also have skin glands which cause them to have a bad taste. But the secretions are not generally as strong as those of toads, so frogs are eaten by a much wider variety of predators. People normally are not affected by the skin secretions of toads and frogs, though human eyes are sensitive to these substances. The pain and burning that result when even a slight amount of skin secretion gets in one of your eyes is something you will never forget.
It is important to wash your hands after handling a toad or frog. The age-old myth that toads can cause warts on people is false.
Toads and frogs are amphibians — a class of vertebrate animals that also includes salamanders and the tropical caecilians, which are long, slender, wormlike, and legless.
Missouri has 26 species and subspecies (or geographic races) of toads and frogs.
Toads and frogs differ from salamanders by having relatively short bodies and lacking tails at adulthood.
Being an amphibian means that they live two lives: an aquatic larval or tadpole stage and a semi-aquatic or terrestrial adult stage.
Of the 6,145 species of amphibians currently recognized in the world, there are approximately 4,145 species of toads and frogs.
The largest species is the goliath frog, Conraua goliath, of the west coast of Africa, which may have a head-body length of nearly 14 inches and may weigh as much as 7 pounds.
One of the world’s smallest frogs is Eleutherodactylus iberia, which has no common name and lives in the tropical forests of Cuba. It is less than a half-inch long as an adult. This frog is so tiny that females of the species are able to produce only one egg during the breeding season.
Even though they are more similar than different, there are some basic physical distinctions.
With practice, you can learn to identify a variety of toads and frogs by the sounds they make. A male toad or frog produces his call by a rapid back-and-forth movement of air over his vocal cords. When calling, a toad or frog will close its mouth and nasal openings and force air from its lungs over the vocal cords into the mouth cavity, then back over the vocal cord and into the lungs. Producing a sound in this closed system enables some toads and frogs enlarged throat or expandable vocal sac to resonate their calls.