A saltwater crocodile attacks a feral pig in Australia
Credit: © Adam Britton, Media Drum World/Alamy Images

Normally invasive species get a bad reputation. They take over ecosystems, reproducing unchecked by predators and eating the native species’ food. The cane toad, native to Central and South America, has dominated regions of Australia, the Caribbean Islands, Florida, Hawaii, Japan, New Guinea, and the Philippines. Zebra mussels hopped aboard a ship in the Caspian Sea and have since clogged up the Great Lakes in the United States. Asian tiger mosquitoes, Burmese pythons, stink bugs, and Japanese beetles also wreak havoc in their new neighborhoods. However, in Australia, there is a plot twist in the invasive species narrative.

The feral pig was taking over Australia beating out livestock for food, damaging fences and water sources, and eating crops before harvest. The pigs were brought by European settlers in the late 1700’s. They soon took over and bred throughout the country. Scientists were beginning to worry the feral pigs would put the ecosystems past the brink of return. Then, the saltwater crocodile stepped in.

Saltwater crocodile
© Firepac, Shutterstock

The saltwater crocodile is the largest living reptile and one of the most fearsome predators on Earth. Adults can reach lengths of 23 feet (7 meters) and weighs of over 1 ton (0.9 metric tons). The saltwater crocodile has a long, low, sausage-shaped body; short legs; and a long, powerful tail, which it uses to swim. It also has a tough hide, a long snout, and sharp teeth to grasp its prey. Saltwater crocodiles have lived on the coasts of northern Australia and Southeast Asia, and on the islands between for millions of years. The saltwater crocodile is also called the estuarine crocodile and the Indo-Pacific crocodile. In Australia, it is informally called the “saltie.”

A saltwater crocodile’s diet depends greatly on its age and size. Young individuals eat crustaceans, insects, rats, and small fish. As saltwater crocodiles grow, they take increasingly larger prey, including sharks and water buffalo. Large adults may attack humans if an opportunity presents itself. The crocodile has had a menu change in recent years, giving a new meaning to the term “piggy bank.” They have recently taken to feral pigs, snatching them up when they go to the water to drink. Pork is on the menu and seems to be a permanent a-la-carte item.

Adult saltwater crocodiles have one of the strongest bites in the animal kingdom. They can close their jaws with approximately 3,700 pounds per square inch of force. In contrast, human bite force is only about 200 pounds per square inch. Those pigs do not stand a chance if the crocodiles hit the mark on the first bite!

Because they present a danger to humans, saltwater crocodiles are sometimes feared and hated by people. In northern Australia, they were hunted almost to extinction before a 1970 hunting ban enabled populations to recover. Like most other crocodiles, saltwater crocodiles are threatened by hunting, invasive species, habitat loss, and pollution. Governments across the saltwater crocodile’s range work to educate people on how to avoid attacks. Scientists in Australia studied the carbon and nitrogen isotopes in bone samples of crocodiles comparing today’s crocodiles to those from almost one hundred years ago. The study found that feral pigs had become the primary food source in the last 50 years. This finding reveals that although crocodiles used to mainly eat aquatic prey, they have adapted to eat mostly prey that lives on land! The crocodiles seem to be making a comeback with their new diet. This invasive species helped out an endangered species! You will be here for a while, crocodile!

Saltwater crocodile
© Firepac, Shutterstock

October 21 is a special day for our scaly friends. Slithering black mambas, majestic leatherback sea turtles, and itty bitty nano-chameleons (just discovered in 2021) step into the spotlight for National Reptile Awareness Day in the United States.

The saltwater crocodile is the largest living reptile and one of the most fearsome predators (hunting animals) on Earth. Adults can reach lengths of 23 feet (7 meters) and weights of over 1 ton (0.9 metric tons). Saltwater crocodiles live on the coasts of northern Australia and Southeast Asia, and on the islands between. The saltwater crocodile is also called the estuarine crocodile and the Indo-Pacific crocodile. In Australia, it is informally called the “saltie.”

The saltwater crocodile has a long, low, sausage-shaped body; short legs; and a long, powerful tail, which it uses to swim. It also has a tough hide, a long snout, and sharp teeth to grasp its prey.

A saltwater crocodile’s diet depends greatly on its age and size. Young individuals eat crustaceans, insects, rats, and small fish. As saltwater crocodiles grow, they take increasingly larger prey, including sharks and water buffalo. Large adults may attack humans if an opportunity presents itself.

Unlike other crocodiles and alligators, saltwater crocodiles swim in the open ocean. They have occasionally been seen swimming far from shore, apparently moving between islands. Saltwater crocodiles are often found in brackish (salty) pools and estuaries, coastal river valleys flooded by the ocean. They can also live in fresh waters, however, including rivers and swamps.

Saltwater crocodiles reproduce during the rainy season. A female saltwater crocodile lays about 50 eggs in a nest of rotting vegetation. The mother may protect the nest from predators. The eggs hatch in about three months. Hatchlings are about 1 foot (30 centimeters) long at birth. The mother carries the hatchlings from the nest to open water to protect them from land predators.

Male saltwater crocodiles grow larger than females. Males reach an average length of about 16 feet (5 meters). Females typically grow to about 11 1/2 feet (3.5 meters) in length.

Adult saltwater crocodiles have one of the strongest bites in the animal kingdom. They can close their jaws with approximately 3,700 pounds per square inch (16,500 newtons) of force. In contrast, human bite force is only about 200 pounds per square inch (900 newtons).

Because they present a danger to humans, saltwater crocodiles are sometimes feared and hated by people. In northern Australia, they were hunted almost to extinction before a 1970 hunting ban enabled populations to recover. Like most other crocodiles, saltwater crocodiles are threatened by hunting, invasive species, habitat destruction, and pollution. Governments across the saltwater crocodile’s range work to educate people on how to avoid attacks.

November 23, 2016

At a recent convention of paleontologists (scientists who study animals and plants that lived in prehistoric times), things got a bit venomous. A group of researchers claimed that a fossil recently identified as an early snake was not a snake at all. Furthermore, they stated that the specimen should not have been studied in the first place. The presentation was the most recent shot fired in the battle over the evolution (a process of change over time) of snakes.

This artist’s impression shows the four-footed tetrapodophis amplectus snatching its prey, an unlucky salamander. Credit: © James Brown, University of Portsmouth

In 2015, Dave Martill and his colleagues at the University of Portsmouth in England reported that they had discovered a new type of primitive snake. They found the ancient animal’s fossilized imprint (which came from Brazil) among the collections of a German museum. The British researchers named their discovery Tetrapodophis amplectus and published their findings in the journal Science. Tetrapodophis means “four-footed snake.” The animal was about 6 inches (15 centimeters) long and possessed four tiny limbs. It lived in an ocean environment some 110 million years ago.

This month, however, at the annual Society of Vertebrate Paleontology conference in Salt Lake City, Utah, Michael Caldwell of the University of Alberta in Edmonton, Canada, gave a presentation refuting Martill’s “four-footed snake” diagnosis. In the creature’s skull, for instance, Caldwell noted “every single character that was identified in the original manuscript as being diagnostic of a snake was either not the case or not observable.” Instead, Caldwell’s group contended that Tetrapodophis is not a snake at all, but rather a member of a group of unrelated marine reptiles.

The fossilized imprint of Tetrapodophis reveals small, specialized feet—or perhaps flippers. Credit: © Dave Martill, University of Portsmouth

This dispute is merely the latest spat among paleontologists on snake origins. Paleontologists agree that snakes likely evolved in the Jurassic Period some 150 million years ago. Some people (like Martill) think that snakes evolved from aquatic reptiles. Over million of years, four-legged reptiles would have spent more and more time in the water, eventually losing their limbs in favor of a long body good for swimming. Later, snakes made their way onto land, with some (sea snakes) remaining in their ancestral habitat. Martill’s group contends that snakes were closely related to mosasaurs, giant marine reptiles that prowled the oceans some 100 million years ago. Most paleontologists, however, think that snakes evolved from burrowing, terrestrial reptiles. As these aimals dug deeper and more complex burrows with their strong heads, their limbs vanished over millions of years. Later, snakes moved into different habitats, including the sea. In this scenario, snakes’ closest relatives would be monitor lizards such as the Komodo dragon. So far, a lack of ancient snake fossils has prevented either hypothesis from being proven.

Further muddying the water, Caldwell—of the “land snake” faction—reported that when he went to study the fossil in the German museum, the fossil was no longer there. Apparently, it had been a loan to the museum from a private collector. The collector had retrieved it from the museum because it had been damaged during an earlier study. Most paleontologists will not study privately owned fossils for this exact reason: an owner may take back the fossil at any time. Science must be repeatable, so a description of a specimen that is no longer available for study is not science at all. Since Tetrapodophis was revealed to be a privately owned specimen, many experts have vowed to ignore it while conducting future studies on snake evolution. We will have to wait for more fossils—in the permanent collections of museums and universities—to determine if snakes started out on land or in the water—with four legs or, perhaps, four flippers.

August 17, 2012

The recent discovery of the biggest Burmese python ever found in Florida is convincing evidence of just how well established these highly destructive reptiles have become in Everglades National Park and other parts of South Florida, according to Florida scientists. The snake was 17 feet 7 inches (5.35 meters) long and weighed 164 1/2 pounds (76 kilograms). Scientists recovered 87 eggs from the snake–also  a record for the state. The pythons “are surviving a long time in the wild,” said snake expert Kenneth Krysko of the Florida Museum of Natural History. “There’s nothing stopping them.” About 1,825 Burmese pythons were discovered in Everglades National Park from 2000 to 2011. However, scientists think the python population is many times higher.

Native to Southeast Asia, the python is classified as an invasive species in North America. From 1999 to 2004, pet exporters met a growing American demand for Burmese pythons by shipping more than 144,000 baby snakes to the United States. However, new owners were frequently unprepared or unwilling to care for the massive snakes in adulthood. Many owners dumped their snakes into the wild. Pythons released into the Everglades, a region with a climate similar to that of the snakes’ native habitat, flourished. Pythons also have escaped into the wild during hurricanes.

Young Indian pythons hatch from eggs outside the mother's body. The leathery shells of snake eggs expand as the young snakes grow inside. When they are ready to hatch, young snakes slash their shells with a special tooth that grows on the upper jaw. (AP/Wide World)

The pythons have devastated the mammal population of the Everglades and were targeting the park’s birds, according to a study released in April 2012. The study was the first to provide evidence linking a sharp decline in populations of medium- and large-sized mammals in the park to an explosion in the number and range of the large snakes. The record-holding snake found recently had feathers in its stomach.

Wildlife experts agree that eliminating the secretive and hard-to-hunt snakes from the park would be impossible. They are unsure if the spread of the snakes, which have no natural predators in North America, can be halted. In January, the administration of President Barack Obama outlawed the import and interstate commerce of Burmese pythons, two other pythons, and the yellow anaconda. Reptile importers are still allowed to trade in reticulated pythons and boa constrictors. Florida permits residents to hunt pythons under certain conditions.

Additional World Book articles:

• Ecology
• Invasive Species (A Special Report)
• Reptile