Mud, Root Balls, And Other Tasty Tidbits In Crocodilian Stomachs


Figure 1. The skin of the black caiman that had the rootball in its stomach.

Cott (1961) reported that most Nile crocodiles, Crocodylus niloticus, more than one year old had stones in their stomachs. He pointed out these stomach stones could be acquired (1) accidentally when grabbing prey, (2) indirectly from the stomachs of prey, and (3) by deliberately swallowing them. Accidental acquisition can be ruled out since most crocodiles in a population contain the same percentage body-weight of stones; older crocodilians do not contain a proportionally greater load of stones. Acquisition from the digestive tracts of prey also can be eliminated, since the prey of many Nile crocodile populations do not ingest stones, e.g., stones are found in young crocodiles that are feeding on invertebrates and amphibians, and adults that feed on pelicans, catfish, and talapia. Indirect support for the deliberate ingestion of stones comes from observation of crocodiles that live in stone-free swamp habitats with soft bottom ooze and travel long distances out of that habitat to find and devour the stones.

Cott (1961) also reviewed the suggested function of stones found in the stomach, e.g., digestive (gastrolith food grinding) function, filling (hunger appeasement) function, and hydrostatic (ballast) function.

While conducting surveys of the caimans of Bolivia, we encountered two caimans, one in 1986 and one in 1995, with items in their stomachs that are so unusual that accidental or inadvertent ingestion seems to be the only reasonable explanation for their presence in the stomachs.


Figure 2. Dante Videz-Roca holding the rootball recovered from the stomach of a Melanosuchus niger.

On 14 July 1986, four adult yacare caiman, Caiman yacare, were collected in the Río Zapacos west of Yaguaru, ca. 15°35' S, 63°14' W, Nuflo de Chavez Province, Santa Cruz Department, Bolivia. The limbs and tail of one of the specimens, UF 120019, appeared lean, but its belly was so grossly swollen that it appeared as though it were about to burst. After the specimen was euthanized, an incision was made in its abdomen to determine the cause of the swelling. The stomach was completely filled with black mud. Mixed in the mud were the remains of crocodilian eggshells, most probably Caiman, but possibly Melanosuchus or Paleosuchus. The mud was washed away and the eggshells retained.


Figure 3. Close-up of the 20.3 cm (8 inches) in diameter ball of roots recovered from the stomach of a black caiman, Melanosuchus niger, in Bolivia. A hole was cut into the side with a knife to establish that the entire ball was composed of roots.

Crocodilians are known to eat empty eggshells and embryonic membranes after the young have hatched (Kushlan and Simon 1981McNease and Joanen 1977Pooley 1977). When a clutch of eggs is developing in the oviducts of a female crocodilian, calcium is stripped from her body to lay down protective shells around the eggs and to add the mineral to the yolk that feeds the growing embryos while they are building skeletal tissue. Consuming the eggshells after eclosion both returns some calcium to the female and removes debris that might attract predators. Clutches of unhatched eggs may also be eaten by adults (Deitz 1979Magnusson 1980;Whitaker and Whitaker 19761984).

The digestive contractions of the stomach may have rolled those first roots into a ball, which provided a bolus around which later roots were wound resulting in the 20.3 cm (8 inch) diameter ball that was found. A ball that large could not be passed through the pelvic girdle or cloaca. Had the caiman not been killed, the ball might have grown to an even larger size.

The mud and stringy roots were too soft to serve a digestive gastrolith function, and while the stomachs certainly were filled, it seems unlikely that the two caimans would have swallowed these materials to serve a hunger appeasement function. Sufficient mud was swallowed to have a hydrostatic effect, but the weight of the roots was far too little. The most probable explanation for how these materials got into the stomachs of these two caimans is they were inadvertently ingested when the animal was swallowing a target item.


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Authors: F. Wayne King, Florida Museum of Natural History, Gainesville, FL 32611-7800, U.S.A., and Robert Godshalk, Department of Wildlife Ecology and Conservation, University of Florida, Gainesville, FL 32611-0430, U.S.A.

Suggested Citation: F. Wayne King and Robert Godshalk. 2003. Mud, Root Balls, and Other Tasty Tidbits in Crocodilian Stomachs. 6 p. [Online] Available at: