American Bullfrog

Rana catesbeiana (Shaw, 1802)

American Bullfrog
American Bullfrog, Will County, Illinois. photo by C.A. Phillips

Key Characters: Well-developed dorsolateral folds tracing rear border of tympanum but not extending onto sides of body; toes webbed nearly to tips.

Similar Species: This is the only large ranid frog in Illinois with no dorsolateral folds extending past the typanum onto the back and no dorsal spots or blotches. See Key to Frogs & Toads of Illinois for help with identification.

Subspecies: None recognized.

Description: Large (9-15 cm SVL) olive, green, or brown frog sometimes with dots or obscure black blotches on back. Backs of juveniles and tadpoles covered with small, evenly scattered black dots. Belly ranges from white to yellow, in some individuals marked with black spots or networks. Tympanum distinctly larger than eye. Males with single vocal pouch under lower jaw, yellow throat, larger tympanum and, during the breeding season, swollen thumbs.

Habitat: Permanent bodies of water (lakes, ponds, rivers, sluggish portions of streams) in forests, prairies, and disturbed habitats (including urban areas).

Natural History: Adult tends to be solitary. Eats any animal it can capture and swallow: arthropods, other frogs, snakes, even small mammals and birds. Bullfrogs have been introduced as food for humans in some parts of the world. Breeding male emits deep bass “jug-a-rum” breeding call. During long summer breeding season (April-August), males sometimes aggressively defend part of pond and mate with entering females. Thousands of eggs are laid in summer as a thin film on top of the water. Tadpoles overwinter and transform the following summer.

Status: Abundant statewide in permanent aquatic habitats.

Etymology: Rana – rana (Greek) meaning frog; catesbeianus – (New Latin) patronym for Mark Catesby (1682/1683 – 1749), English naturalist and illustrator.

Original Description: Shaw, G. 1802. General Zoology or Systematic Natural History. Volume III, Part 1. Amphibia.  London: Thomas Davison.

Type Specimen: Not known to exist.

Type Locality: “many parts of North America . . . Carolina . . . . Virginia”

Original Name: Rana catesbeiana Shaw, 1802

Nomenclatural History: Frost et al. (2006, Bull. Am. Mus. Nat. Hist., 297: 369) removed catesbeiana (and most other North, Central, and South American ranids) from Rana and placed it in Lithobates based on extensive DNA sequence data, but not all workers agree with this arrangement because of the instability this brings to well-known taxa such as Rana catesbeiana. AmphibiaWeb recommends using Rana (Lithobatescatesbeiana to demonstrate that it is a member of the subgenus Lithobates while preserving long-standing taxonomy.