from the book, "Our Fascinating Earth"
The celebrated croaking concert of the male frog during mating season is his only effort to attract a mate. The tactics he uses would be as effective for attracting prey, for as soon as a female, or a reasonable facsimile, swims by, he seizes her in a tight wrestler's grip and squeezes her until the spawn is expelled. Then he fertilizes the egg mass.
During the mating season it is not unusual for male frogs to yield to a form of mass mating hysteria. A male will jump on the back of another male or a stone or a piece of wood. They become so frantic that two males or more may jump on the same female. It is not unusual for a male to leap on the back of another male who is busily riding a female and ride him piggyback. Male victims usually struggle free of their attackers. Those who grab a stone or piece of wood drop the object as soon as they realize that is doesn't look, feel, or act like a frog.
In the midst of the mating hysteria it is not unusual for a male frog to grab a lump of mud. Apparently a lump of soft mud feels very much like a female, because he holds on very tightly. The mud becomes so modeled in his grasp that it assumes the modified shape of a frog. The male, deceived by the mud frog of his own creation, may hold on for days, waiting in vain for the captive lump to release spawn.
It is quite safe to assume that frogs have been around for well over 300 million years. During that time many species have developed very successful and unique methods of spawning.
In the land and water world of the amphibians the eggs of most species lack a protective membrane or shell to prevent the embryos from drying out. Hence the eggs must be laid in water, which introduces another crucial problem: how to keep the eggs safe from aquatic predators. The foam—nesting frogs of the African savannas have evolved an unusual solution. They keep their eggs safe from predators that might swim near by not laying them in water at all. For an amphibian this seems immensely foolhardy, but the foam—nesting frogs have worked it out rather well.
During mating season both males and females gather in a pond. They usually emerge in groups of up to forty, climb a nearby tree, and crawl out on a branch overhanging the pond. Once they are out on the limb the females secrete mucus on it. Immediately all the frogs collectively begin to kick madly with their hind legs, whipping the secretion into a froth. What a sight to behold — forty or so frogs all in a frenzy, performing a ritual dance as they kick the mucus into a white, foamy meringue! Once the froth is well developed, the frogs spawn in it and lay their eggs.
Immediately after the eggs are laid, the frogs depart, their mission in life now complete. The froth quickly hardens on the outside, protecting the embryos from dehydration and very likely also from land—dwelling predators. In about four days the well—developed tadpoles begin to emerge from their eggs. By wriggling sufficiently they manage to make a hole in the outside shell of the froth. They emerge from it and drop several feet directly into the pond below. Their life as free—moving vertebrates has now begun.