Missouri's Toads and Frogs
1982 (c) Missouri Conservation Commission
Reprinted from the Missouri Conservationist
by Tom R. Johnson
Herpetologist
Jefferson City, MO
Photos by Author
 

Missouri toads and frogs are colorful, harmless, vocal and valuable. Our 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. Studying these animals and sharing their stories with fellow missourians is one of the most pleasurable and rewarding aspects of my work.

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 25 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 (tadpole) stage and a semiaquatic or terrestrial adult stage. Of the 3,260 species of amphibians currently recognized in the world, there are approximately 2,770 species of toads and frogs. The largest species is the Goliath frog, Rana Goliath of the west coast of africa which may have a body length of nearly 14 inches and may weigh as much as five pounds. One of the world's smallest frogs is Sminthillus limbalus which has no common name and lives in the tropical forests of cuba. It is only a half-inch long. This frog is so tiny that females of the species are able to produce only one egg during the breeding season.

An egg mass from the wood frog          Some tadpoles are beautifully

                                       colored (eastern gray treefrog).
 
 

One often-asked question is: "What are the differences between toads and frogs?" While they are more similar than different, there are some basic distinctions. Toads have dry, warty skin, while frogs have smooth, wet kin. Toads do not have teeth; frogs have tiny teeth on both upper and lower jaws. Toads have shorter hind legs than most frogs. Toads hop, frogs jump. Female toads lay their eggs in long, parallel strings; female frogs-depending on the species-lay their eggs singly, in small clumps, in large clumps, or as a film of eggs on the water surface.

Although most people would be hard-pressed to identify a variety of toads and frogs by the sounds they make, people generally are aware of the fact that these animals have voices and are interesting to listen to. 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 cords and into the lungs. Producing a sound in this "closed system" enables some anurans (toads and frogs) to vocalize under water. These animals use an enlarged throat or expandable vocal sac to resonate their calls.

All missouri toads and frogs must return to a body of water to reproduce. Most of our species breed during the spring or early summer, but southern leopard frogs, Ranasphenocephala, are knownto breed during rainy periods in the fall. The majority of these amphibians select fishless bodies of water in which to breed. Flooded fields, ditches, small woodland ponds, prairie ponds and water-filled depressions are favorite places. A few hardy, 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 which 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, 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 anuran eggs hatch within 10 days of being laid, but they may hatch much sooner if the water temperature is above 21 degrees celsius (70 degrees fahrenheit). 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. Tadpoles of most of our species eat aquatic plants-especially algae-as they fish, 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 lost, 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 froglet, is the combination of the disappearance of the tail and the change from a life under water 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 way. Most of their enemies are predators such as fish, turtles, snakes, birds and carnivorous mammals-shrews, mink, skunks and raccoons. Our larger species of frogs will also eat other frogs. Toads cannot jump as fast as frogs to escape a predator and defend themselves by producing toxic or unpleasant-tasting skin secretions which are released when the animal is seized. Due to their bad flavor, toads are not a popular food among predators. Even their eggs and tadpoles are said to be toxic. Frogs also have skin glands which cause them to have a bad flavor, but the secretions are not generally as strong as those of toads, and so frogs are eaten by a much wider variety of predators. People normally are not affected by the skin secretions of toads and frogs, although human eyes are sensitive to these substances. The pain and burning that result when even a slight amount of anuran 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.

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. Just hearing or seeing them adds to our enjoyment of the missouri outdoors. Their role in nature can be illustrated by the huge number of insects they eat and by the number of animals that eat toads, frogs or their tadpoles. And, a discussion of the value of frogs should include the fact that literally thousands of bullfrogs are harvested in our state each year for human consumption-one of missouri's truly gourmet outdoor foods.