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American bull frogs

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American bull frogs

The American bull frog (rana clamitans Latreille) is the largest of the bullfrogs. It can be found throughout Eastern North America from Canada, west to eastern Minnesota, Iowa, eastern Kansas, southeastern Oklahoma, southeastern Texas and south to Florida and Louisiana. This is the largest frog in North America.

This bullfrog will become from 3.5 to 6 inches but mostly will be under 4 inches, sometimes to 5 inches. Characteristics will include the above part being brown, greenish brown or even dusky olive, sometimes black spots are present usually on the posterior. The head and shoulders are bright green. In the gular area there is sometimes a dusky mottling also on the chest and undersides of the femora. The legs have dusky bars or spots with the hind part of the femur having spots and blotches of dusky also. It has well-defined dorsolateral folds that seldom extend much posterior to the sacral hump with webbing on the hind foot slightly less developed, not reaching the tip of the fourth toe. It has shown to commonly join the toe at the base of the second phalanx from tip of the toe. There is a yellowish-white streak along the edge of the upper jaw extending posteriority to the shoulder. The iris of the eyes will be golden. This frog could also have a netlike pattern of gray or brown on a green background. The throats of the males are white with mottled gray and a yellowish wash. In some ranges of the United States especially in Florida the bullfrog can become patterned with brown or dark gray. The younger frogs will have a head and eyes a little large in proportion to the rest of the body. The recently metamorphosed young may have dorsolateral folds. There can be present dorsal patterns of scattered small dark spots, the limbs may be speckled and have blotches of dark color and the blow whitish, gular area may be flecked with dusky. The male can be distinguished from the female as he has a yellow or orange-yellow throat with his eardrum larger than his eye and a greenish-yellow spot or ring at the center. The female will not have the yellow color on her throat in addition her tympanum will be smaller, the head more narrow and her skin will be smoother than the male.

This species of bullfrog loves water more than other frogs. It will live in small areas of water if necessary but does prefer large bodies of water. This bullfrog may be found around large areas of water such as rivers, lakes, large ponds and in swamp areas. It will hide in vegetation along the sides of the banks of the water.

This bullfrog will eat practically anything. It principally likes insects and other arthropods, crayfish, and even will eat other small frogs. Mollusks, crustaceans, millipedes, arachnids and caterpillars are part of the diet of the American bullfrog. It will eat earthworms, fishes, odonatans, mecopternas, ephemerids, centipedes, mites and undetermined insects. Since he eats small fish, tadpoles and aquatic insect larvae it is known that he will capture some food beneath the surface of the water. Non aquatic insects will be a source of much of his food.

The vocal sacs are paired and lateral with the throat appearing as a flattened pouch when it is inflated. The voice of the bullfrog is as the plucking of an elastic cord being stretched ever so tightly over an empty box. It has a bass sound relating to a "bung" or "plug." There will be several repeats of this sound accompanied by several croaking notes. These base notes will be heard at intervals of about one and one half minutes. Sometimes there is just a single "clung" or "c'tung" but other times there will be a rapid succession of several notes as in "clung-clung-clun-clung" or "c'tung." The sound will not carry very far as it is not loud. The older frogs will have a lower pitch when jumping in the water such as "ch-u-n-ng" or "k-tun-n-ng" as their croaking is different from the younger bullfrogs. This short, high-pitched cry is approximately like the sound of someone being afraid. The sounds will be reapeated as the bullfrog takes a dive to safety or leaps in the air. It may be repeated as many as six times in succession.

The bullfrog will hibernate during the winter months. It is also solitary except for the time when breeding occurs.

Breeding occurs from May to mid-August in the eastern United States and from February to October in the southern United States. The male will attach himself to a female, with the female lowering her head enough to submerge, bowing the back down. This process will have her cloaca raised just out of the water with her limbs extended and spread. The male will shift forward, moving his hind limbs so that their shanks rest on his laterally projected thighs. As the female's abdomen contracts, he moves his feet forward, brings them together and places his heels anterior to the two cloacas. The female will expel a batch of up to fifty eggs that spread out between the male's feet, almost touching his cloaca they will be covered with seminal fluid. He will then push the eggs away so they will spread to the surface a little distance behind them. There will be a second cycle of these movements continue rhythmically until the female as spent all the eggs. The eggs become surface film, less than one square foot in extent, from 7 inches by 12 inches. These eggs are usually deposited around the margins of ponds, and may be either free or attached to some vegetation. There are usually from l,000 to 5,000 eggs in a single layer outlined on the surface. The eggs have 2 gelatinous envelopes, the inner one is 2.8 to 4.0 mm, and the average size is 3.3 mm. They can be circular, pyriform or elliptical but will be always distinct with the outer ones being 5.0 to 6.0 mm. This merges into jelly film, with ovum 1.2 to 1.8 mm, the average being 1.5 mm. They will be black above and white below.

The larva will be the size of a tadpole as it is large, but not deep-bodied, with a length of body being 12.1 to 27.8 mm, the tail, l8.4 to 47.0 mm. The tail will be fairly elongated with the tip acute, the dorsal fin not as wide as musculature. It will extend forward on the body slightly ahead of the vertical of buds on the hind legs, spiracle sinistral, just visible from the dorsal aspect. It will be directed obliquely upward and backward, spiracle below the lateral axis. There will be a spiracular opening elliptical, muciferous crypts distinct in life, indistinct in most preserved specimens. An eye will be on or above the lateral axis and near the lateral outline in the dorsal aspect more so than in the mid dorsal line. The anus will be dextral opening on a level with the edge of the ventral fin.

There will be labial teeth measuring 2/3 or l/3 with the edge of the upper labium fringed with teeth and about equal to the upper horny beak in the length. In the corners beneath this fringe there will be a short row from 2/15 to 1/15 on the upper row with the ends being lateral rows. These will not extend beyond the end of the upper row. The median space between the lateral rows will be up to ll times the length of either row. The first lower labial row will be slightly longer or equal to the horny beaks in the length. It can be divided in the middle with the second row equal to the first and the third row being shorter, about ? of the first now.

Sometimes in the labatory setting the larvae transform in 92 days after insemination but usually it takes about 113 days. The early breeders will produce larvae that will transform the same year as the eggs are laid but late breeders will not transform until the next year. In some cases it can take two years for the eggs to mature.

Written by Robert Starnes