Alligators intentionally consume stones, a behavior known scientifically as lithophagy. These stones, called gastroliths (meaning “stomach stones”), are a deliberate physiological adaptation. Swallowing stones provides the alligator with internal tools that contribute to the efficient processing of food and the management of its weight in water.
The Role of Gastroliths in Digestion
The American alligator has a two-part stomach, similar to the digestive system found in birds. The first section is a highly muscular chamber, the ventriculus or gizzard, where the gastroliths are housed. This section acts as a mechanical grinder, with the stones serving as the grinding media.
Alligators frequently swallow prey whole or tear off large chunks, as their teeth are not designed for chewing. Powerful contractions of the ventriculus churn the food against the abrasive gastroliths. This grinding action physically breaks down resistant components such as bone, scales, and thick hides.
The mechanical breakdown significantly increases the surface area of the food particles. This allows the alligator’s potent gastric acids and digestive enzymes, secreted in the second stomach chamber, to work more effectively. The combination of mechanical grinding and chemical digestion ensures maximum nutrient extraction from large, infrequent meals.
Weight Management and Buoyancy
Beyond digestion, gastroliths serve a hydrostatic role, acting as internal ballast for the aquatic reptile. Alligators spend significant time submerged, and the added weight of the stones increases their specific gravity. This extra density counteracts the natural buoyancy of their lungs and fatty tissues, making it easier for the alligator to sink and remain on the bottom without expending effort.
Recent studies on juvenile alligators demonstrated a direct link between gastroliths and diving performance. After ingesting stones equivalent to approximately 2.5% of their body mass, the alligators’ average voluntary dive time increased by nearly 88%. This gain is due to the animal’s ability to maintain negative buoyancy while simultaneously taking a larger volume of air into its lungs.
The stones allow the alligator to carry a larger oxygen reserve without floating to the surface, a major advantage for an ambush predator. This ballast also helps stabilize the animal, preventing it from rolling or drifting in currents while waiting for prey.
How Alligators Select and Process Stones
Ingesting stones is a deliberate behavior, though the exact selection mechanism is not fully understood. Alligators appear to choose stones that are smooth, dense, and rounded, which are the most effective shapes for grinding and least likely to cause injury. Field observations have documented alligators carefully picking up gravel and swallowing it.
Once swallowed, the stones can be retained within the ventriculus for extended periods, sometimes years. The stones are worn down over time by constant grinding and the corrosive effect of stomach acid. The alligator eventually expels the gastroliths, either by regurgitation or by passing them through the digestive tract.
The size and number of gastroliths vary significantly based on the alligator’s age and diet. Larger, older alligators tend to contain a greater mass of stones, corresponding to the larger prey they consume and a greater need for ballast in deeper water. This cycle of ingestion, retention, wear, and expulsion highlights the active management of these internal tools.