Missouri’s 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 our work.
Toads and frogs are amphibians—a class of vertebrate animals which also includes salamanders. Missouri has 26 species and subspecies of toads and frogs. Toads and frogs differ from salamanders by having relatively short bodies and lacking tails at adulthood. Being an amphibian means they live two lives, an aquatic larval or tadpole stage and a semi-aquatic or terrestrial adult stage.
One often-asked question is, “What are the differences between toads and frogs?” Even though they are more similar than different, there are some basic physical distinctions. Frogs have smooth, wet skin, while toads’ skin is dry and warty looking.
With practice, people 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 opengins 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 to vocalize underwater. These animals use an enloarged throat or expandable vocal sac to resonate their calls.
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, 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 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 and are grasped by a male in an embrace and begin the process of egg-laying. During egg-laying, the male’s vent opening is positioned just above the females vent and as her eggs are released, the male will fertilize them. He will retain his firm grip on her until all the eggs have been laid.
Most hatch within 10-14 days of being laid, but they may hatch much sooner if the water temperatures is above 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. Most Missouri tadpoles eat aquatic plants, especially algae, as they develop in the wetland. Tadpoles have gills, somewhat like 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 not used, and the last-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, 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. More next week about Missouri’s toads and frogs and the opening of frog season.
From “Missouri’s Toads and Frogs” by Jeffrey T. Briggler and Tom R. Johnson, herpetologists.