Animal Diversity Web

Geographic Range

Southeastern US, ranging from eastern Texas to south central South Carolina, extending south into peninsular Florida (npwrc 1999)

• Biogeographic Regions
• nearctic
  • native

Habitat

Generally, these frogs are distributed in most waterways, such as rivers, streams, lakes, ponds, swamps and marshes (Bartlett 1999). The pig frog inhabits the open centers of cypress ponds, which are an extension to, or separation from the prairies. They prefer ponds with the following vegetation types: waterlilies, hard heads, never wets, wampee, watershield, bladderworts, floating hearts, pickerel weed, saw grass, and maiden cane (Wright 1932).

• Aquatic Biomes
• lakes and ponds
• rivers and streams

Physical Description

The pig frog ranges in length from 3.25 to 5.5 inches. Their appearance is that of a "bullfrog" with a rather narrow and pointed head and fully webbed hind feet. The fourth toe is webbed nearly to its tip. Pig frog coloration is olive to blackish brown with scattered dark spots. Its venter is white or pale yellow with a pattern that is the colors brown, dark gray and black woven into a net on the thighs. The thighs also have a light line or a row of light spots running across their rear. The Pig frog has no dorsalateral ridges (Conant and Collins 1998). In this frog, the tibia is the same length as the femur. Their eyes are greatly elevated and unusually large, with only a narrow space between them. Nostrils are prominent in Lithobates grylio. They have an elevated fold of skin over the ear that runs to the shoulder, and the ear is orange-brown in color with a green center. The middle and posterior back may have four longitudinal bands of bright orange-brown, alternating with bands of olive (Dickerson 1931).

Pig frogs are sexually dimorphic in size and coloration. Males and females have similar growth rates until the snout-vent length reaches about 100mm. After that, the females grow faster and will eventually reach a larger size than the males (Wood 1998). The male's ear is greatly larger than its eye, whereas the female's ear is equal in size to the eye. Perhaps the most distinguishing characteristic is that males have a bright yellow throat (Dickerson 1931).

Mature tadpoles are very colorful. They have a yellow belly with prominent reticulation on brownish black. Their sides have yellow spots that are encircled by a pinkish color. From the throat region to the pectoral region is clear black and across the pectoral region is green. The yellow spots surrounded by pink continue down the tail in various patterns (Wright 1932).

• Other Physical Features
• ectothermic
• bilateral symmetry

Development

• Development - Life Cycle
• metamorphosis

Reproduction

Little appears to be known about the reproduction of Pig frogs. Published observations are based on very few cases.

Immense choruses of Lithobates grylio erupt at night, when the vast majority of the mating occurs. Rainy, overcast or humid overcast weather seems to provide conditions that make for active mating. Breeding season is thought to begin in late May and continue through to August. They breed when the air is humid with temperatures ranging from 63-78 degrees.

The egg laying process is probably similar to that of the bullfrog (Rana catesbeiana) (Wright 1932).

After mating, approximately 10,000 eggs are laid (Bartlett 1999). The eggs are usually attached to pickerel weed stems in the middle of the pond or on the islands of a cypress pond. They can be found amongst saw grass, maiden cane, and wampee. The eggs, which are small and bead-like, are laid in large masses on the surface of the water. The hatching period is 2-3 days. These eggs appear to have no animal predators; their only threat is the receding water (Wright 1932).

Tadpoles are quite large (100mm), with extremely long tails. Although uncertain, Wright speculates that Lithobates grylio may go through metamorphosis after one year. Bartlett (1999) comments that tadpoles in the northern range of this species reportedly take longer than one year to metamorphose whereas those in the southern part of the range develop in less time. After transformation, the young frogs will remain in the same habitat as adults (Wright 1932).

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)

Behavior

As mentioned before little is known of the life of this frog. From what has been observed, they seem to be a shy species, that is easily startled (Bartlett 1999). They are rarely seen in the daylight, and are usually found hiding in aquatic vegetation. They are entirely aquatic, always surrounded by vegetation, and are rarely seen on land.

Although the pig frog is compared in many senses to the bullfrog, their voices are entirely different. Instead of the jug-o-rum of the bullfrog, this frog has a sound that is likened to the sound of the grunting of a herd of pigs (Wright 1932). A single, broadly expanded internal vocal sac (Bartlett 1999) produces this sound.

• Key Behaviors
• motile

Food Habits

The Pig frog is mainly active at night and does most of its feeding at this time. Its primary diet consists of insects and crustaceans (Capula 1989).

Economic Importance for Humans: Positive

Pig frogs are hunted for human consumption, as a source of frog legs.

Conservation Status

No special status known.

• IUCN Red List

  Least Concern
  More information

• CITES

  No special status

Other Comments

Although the pig frog has no special status, there is speculation that their population could be declining. This species has been a staple in the frog leg industry and have been hunted at night by air and John boats. The hunters report that the pig frog population seems to be diminished, however it could just be because populations decline in drought years and erupt in wet years (Bartlett 1999).

Contributors

Bree Herrmann (author), Michigan State University, James Harding (editor), Michigan State University.

References

Accessed October 12, 1999 at http://www.npwrc.usgs.gov/narcam/idguide/rgrylio.htm.

Bartlett, R. 1999. A Field Guide to Florida Reptiles and Amphibians. Houston, Texas: Gulf Publishing Company.

Capula, M. 1989. Guide to Reptiles and Amphibians of the World. New York: Simon & Schuster's.

Conant, R., J. Collins. 1998. A Field Guide to Reptiles and Amphibians Eastern/Central North America. New York: Houghton Mifflin Company.

Dickerson, M. 1931. The Frog Book. Garden City, New York: Doubleday, Doran and Company, Inc..

Wood, K., H. Percival, J. Nichols, J. Hines. 1998. Size-sex Variation in Survival Rates and Abundance of Pig Frogs, Rana grylio, in Northern Florida Wetlands. Journal of Herpetology, 32: 527-535.

Wright, A. 1932. Life Histories of the Frogs of Okefinokee Swamp-Georgia. New York: The Macmillan Company.

Wright, A., A. Wright. 1949. Handbook of Frogs and Toads of the United States and Canada. Ithaca and London: Comstock Publishing Associates.