How do Frogs Digest Food?

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Amphibians typically feast on live prey in the wild and have unique methods concerning their consumption methods. These special feeding habits and behaviors have left plenty of animal lovers wondering how frogs digest their food. 

Frogs eat live prey, which travels to the stomach via the esophagus and dies by drowning in stomach acid or suffocating. The food then follows the small intestine, where it is broken down and absorbed, after which it enters the large intestine and is excreted through the external cloaca.

Frogs typically eat prey small enough to swallow, as they do not have teeth for chewing.

They have to digest their food whole and live, and they need to force down their food using specific eye and limb motions.

A frog’s digestion process begins after the food has been swallowed, as it enters the esophagus in preparation for absorption. 

Although the way frogs consume food differs from many other animals, many of their digestive system features and functions are somewhat similar.

Join us as we discuss how frogs digest their food after consumption and which bodily components aid the process. 

The Frog Digestive System

Digestion begins after the frog swallows its prey, but the complete digestive system starts with the mouth and ends with the cloaca. Frogs lick up and swallow their prey, and only use their small teeth to hold it back, not to chew.

The entire process typically takes 24 hours, depending on the prey. Below is an outline of the main bodily components that make up a frog’s digestive system, as well as their functions throughout the digestion process: 

SystemCharacteristics and Functions
Mouth The mouth marks the beginning of the alimentary canal, extending from each side of the frog’s snout. The upper jaw is fixed, while the lower jaw is flexible for motion. 
Buccal CavityThe buccal cavity is wide, shallow, and large, ciliated with columnar epithelial lining containing mucous glands. Frogs do not have salivary glands, but mucus lubricates the prey for further digestion. 
Pharynx The pharynx is a short cavity that links the buccal cavity to the esophagus and tapers near the gullet. The pharynx also has various links to other body parts, such as the middle ear. 
Esophagus The esophagus of a frog is a short, muscular, and wide tube with a glandular lining that secretes alkaline digestive juices. The tube contains some mucous glands for lubrication, and it is lined with longitudinal folds that permit expansion when prey is swallowed. The esophagus enlarges at the base as it joins with the stomach’s peritoneal cavity. 
StomachThe stomach can be used for food digestion or storage and sits on the left side of the frog’s body, measuring around 1.5 inches. Numerous longitudinal folds line its inner surface, and multicellular gastric glands secrete enzymes and acids. Stomach wall contractions aid the disintegration of food and blending of digestive enzymes, and the food can remain in the frog’s stomach for approximately 2-3 hours.
Small IntestineOnce the food is semi-digested and liquified, otherwise known as chyme, it enters the small intestine. The small intestine is a long, narrow, coiled tube measuring around 11 inches. Food is primarily digested and absorbed in the small intestine, and complete digestion is aided by bile, pancreatic juice, and succus entericus. 
Large Intestine or RectumThe large intestine or rectum is a short and wide tube that prepares and stores feces, measuring at around 1.5 inches (CTNF). It runs to the cloaca and is protected by the anal sphincter.
CloacaThe anus and urinogenital apertures open into the cloaca. The cloaca is a small, terminal, sac-like structure that opens to the outside through a vent at the end of the body. Waste products are excreted through the cloaca after the digestion process. 

The pancreas and liver are incredibly important for digestion and nutrient absorption, as they help convert food molecules to useful nutrients.

The liver creates bile and runs through the pancreas. The pancreas of a frog is branched and irregular, secreting pancreatic juice containing numerous digestive enzymes. 

How Prey Dies After Consumption

In many cases, the prey dies quickly after consumption. However, some frogs eat larger prey, such as large invertebrates and small mammals.

In these instances, the prey may be seen squirming around inside the frog’s belly as it struggles to survive and escape its fate.

There is little to no chance of survival as many dangers await inside the frog’s digestive system. The most common means of fatality for prey once inside a frog’s digestive system include the following:

ReasonEffect in Frog Digestion
Lack of OxygenThe prey does not live long without access to oxygen. Prey may die shortly after consumption by suffocation. 
Stomach AcidIf the prey survives for longer, they will likely pass away once they reach the frog’s stomach acid. The acid will cause disintegration, but prey may also die as a result of drowning.
Digestive EnzymesThe frog’s body will begin creating digestive enzymes throughout the process, which will start breaking down the prey for absorption. 

Does The Prey Always Die Inside a Frog?

Small invertebrates may be able to escape by climbing back up the esophagus before it reaches the digestive tract. However, there are some rare cases of prey being able to traverse through the frog’s digestive system and leave via the cloaca.

In a study conducted by a Japanese biologist in 2020, a species of aquatic beetle was found be to be resistant to pond frog digestion (Sugiura, 2020).

It was found that the beetle actively traveled through the frog’s intestinal tract within only a few minutes by swimming or crawling.

Following the tract at high speeds minimizes the beetle’s exposure to other threats such as acids and extreme conditions inside the frog’s digestive system. 

Suffocation is a threat throughout the process, and this aquatic beetle is aided by its ability to trap an air pocket underneath its carapace for underwater breathing.

The final challenge for the beetle is escaping through the frog’s anal sphincter, and the beetle stimulates the hindgut to induce excretion, allowing it to escape. 

More About How Frogs Eat

While frogs use unique methods for capturing and swallowing their prey, many of their digestion processes are similar to other animals.

Slo-Mo Walkthrough of How Frogs Eat!

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They primarily digest food using stomach acids, intestinal systems, and muscular contractions. The process is supported by the secretion of lubricative mucous and various digestive enzymes.

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Sources 

Sugiura, S. (2020). Active escape of prey from predator vent via the digestive tract, Current Biology, 30, R841-R870.