Keys to Nature
Key to Calumet Region Frogs and Toads

© Alan Resetar - Keys to Nature Project

Key to Calumet Region Frogs and Toads
Alan Resetar, Collection Manager, Division of Amphibians and Reptiles, Field Museum of Natural History, 1400 S. Lake Shore Dr., Chicago, Illinois 60605-2496 USA, 1-312-665-7768
Lay people, citizen scientists and natural resource professionals can use this key to identify Calumet Region frogs and toads. The only Chicago Region frog not in the key is the plains leopard frog (Rana blairi). For a one page field guide to Chicago Region frogs, see A one page field guide to the amphibians and reptiles of southeastern Chicago and northwestern Indiana can be found at Thanks to Bil Alverson and Jennie Kluse for all of their advice and assistance.


Key Structure:
1a. Bony ridge and flat, oblong, bean-shaped parotoid gland behind bulge over each eye; warty skin - 2
1b. Lacks bony ridge and parotoid gland behind bulge over each eye; warty, granular, or smooth skin - 3

2a. Belly mottled with dark pigment - American toad (Bufo a. americanus)
2b. Belly unspotted - Fowler's toad (Bufo fowleri)

3a. Expanded clinging disk on each toe tip varies in size from slightly wider than toe itself to much wider - 4
3b. Lacks clinging disks on toe tips - 7

4a. Three parallel stripes on back & one on each side; light line bordering mouth - Western chorus frog (Pseudacris triseriata) & Boreal chorus frog (Pseudacris maculata)
4b. Lacks three stripes on back and light line bordering mouth - 5

5a. Large X-shaped mark on back - Northern spring peeper (Pseudacris c. crucifer)
5b. Lacks X-shaped mark on back - 6

6a. Large clinging disks on toe tips; white patch beneath eye; granular skin - Gray treefrog (Hyla versicolor & Copes gray treefrog (Hyla chrysoscelis)
6b. Minute clinging disks on toe tips;; lacks white patch beneath eye; warty skin - Northern cricket frog (Acris crepitans)

7a. Discrete spots on back - 8
7b. Lacks discrete spots on back, only random dark mottling or minute black dots on back - 9

8a. Rounded spots on green back; hidden surfaces of hind legs not orange or yellow - Northern leopard frog (Rana pipiens)
8b. Squarish spots in two parallel rows on middle of back; back not green; hidden surfaces of hind legs orange or yellow - Pickerel frog (Rana palustris)

9a. Dorsolateral ridges extending down back - 10
9b. Dorsolateral ridges not extending onto back - American Bullfrog (Rana catesbeiana)

10a. Overall green coloration; eyes not within dark mask - Green frog (Rana clamitans melanota)
10b. Overall light to dark brown coloration; eye within dark mask-shaped marking - Wood frog (Rana sylvatica)


Clinging disk: enlarged disk at the end of a frog digit used for adhering to surfaces.
Dorsal: the back.
Dorsolateral ridge: fleshy ridge of skin extending along the upper side (shoulder area down to above insertion of hind limb).
Dorsum: the back.
Parotoid gland: bean-shaped gland located behind the eye of a toad.
Tympanum: eardrum.
Venter: lower surface of the body (i.e. the belly).


Please email with questions or concerns.
This page was last modified on: Fri, 21 May 2010 22:16:35 -0500.