The Northern Leopard Frog

Published
03/26/2014 by

 

 

 

  

The northern leopard frog swallows its prey using its eyes — it uses them to help push food down its throat by retracting them into its head.

 

Named for the spots across their green backs, northern leopard frogs will eat just about anything that crosses their paths.

 

Photo: Leopard frog

Photograph by Bates Littlehales

 

The northern leopard frog is perhaps most recognizable as the formaldehyde-soaked specimen in the high school lab tray.

 

Once the most abundant and widespread frog species in North America, leopard frogs were widely collected not only for dissection but for the food industry (frog legs) as well.

 

However, massive declines beginning in the early 1970s, particularly in Canada and the western United States, have significantly reduced their numbers. Scientists have not determined the cause of the declines, but it is likely a combination of ecological factors: pollution, deforestation, and water acidity.

 

Northern leopard frogs are so named for the array of irregularly shaped dark spots that adorn their backs and legs. They are greenish-brown in color with a pearly white underside and light-colored ridges on either side of their backs. They are considered medium-size, reaching lengths of 3 to 5 inches (7.6 to 12.7 centimeters), nose to rump. Females are slightly larger than males.

 

Their range is most of northern North America, except on the Pacific Coast. They generally live near ponds and marshes, but will often venture into well-covered grasslands as well, earning them their other common name, the meadow frog.

 

Leopard frogs will eat just about anything they can fit in their mouths. They sit still and wait for prey to happen by, then pounce with their powerful legs. They eat beetles, ants, flies, worms, smaller frogs, including their own species, and even birds, and garter snakes.

 

Map

 

Map: Leopard frog range

Northern Leopard Frog Range

 

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Fast Facts

Type: Amphibian
Diet: Carnivore
Average life span in the wild: 2 to 4 years
Size: 3 to 5 in (7.6 to 12.7 cm)
Group name: Army
Protection status: Threatened
Did you know?  A genetic mutation gives rise to the Burnsi leopard frogs, which have no spots.
Size relative to a tea cup:
Illustration: Northern leopard frog compared with tea cup

 

 

Contribution of eye retraction to swallowing performance in the northern leopard frog, Rana pipiens


  1. Robert P. Levine1,*
  2. Jenna A. Monroy2 and 
  3. Elizabeth L. Brainerd1
 
 
Most anurans retract and close their eyes repeatedly during swallowing.

Eye retraction may aid swallowing by helping to push food back toward the esophagus, but this hypothesis has never been tested. We used behavioral observations, cineradiography, electromyography and nerve transection experiments to evaluate the contribution of eye retraction to swallowing in the northern leopard frog, Rana pipiens.

Behavioral observations of frogs feeding on 1.5 cm long crickets reveal a high degree of variability in eye retraction and swallowing. Eye retraction can occur bilaterally or unilaterally, and both swallowing movements and eye retraction can occur separately as well as together.

During swallowing, cineradiography shows that the eyes and associated musculature retract well into the oropharynx and appear to make contact with the prey item. This contact appears to help push the prey toward the esophagus, and it may also serve to anchor the prey for tongue-based transport.

Electromyographic recordings confirm strong activity in the retractor bulbi muscles during eye retraction. After bilateral denervation of the retractor bulbi, frogs maintain the ability to swallow but show a 74% increase in the number of swallows required per cricket (from a mean of 2.3 swallows to a mean of 4.0 swallows per cricket).

Our results indicate that, in Rana pipiens feeding on medium-sized crickets, eye retraction is an accessory swallowing mechanism that assists the primary tongue-based swallowing mechanism.