When one thinks of crocodiles, one does not usually think of them as showing up in the United States, but they do. Crocodiles and alligators belong to a group of reptiles called crocodilians, which are the largest of the living reptiles. Of the 23 different species of crocodilians in the world, 2 species are native to the United States and south Florida is the only place where both of these species coexist.
The American alligator ranges throughout the southeastern United States. American Crocodiles on the other hand, inhabit coastal areas of south Florida where they are at the northern extreme of their range. American crocodiles also can be found on the islands of Cuba, Jamaica, and Hispaniola, as well as along both coasts of southern Mexico and Central America, south to Ecuador on the Pacific coast of South America, and Venezuela on the Atlantic coast.
At first glance crocodiles can be difficult to distinguish the two, but there are important differences. The American crocodile is lizard-shaped with a long, muscular tail and four short legs that have five toes on the front feet and four on the back feet. Adults have grayish-green backs and tails and white to yellowish undersides. Their narrow snout is triangular in shape, and the fourth tooth on both sides of the lower jaw is visible when the mouth is closed. The ear drums are protected by movable flaps of skin at the top of the head behind the eyes, and the nostrils are at the end of the elongated snout. Because of the location of the eyes, ears, and nostrils, a crocodile can be submerged with only the top of its head exposed and still be able to see, hear, and breathe. Male crocodiles can reach about 20 feet in length but rarely exceed 14 feet in the wild. Mature females are about 8 to 12 feet in length.
Alligators are more numerous in Florida than crocodiles and are darker, have a broader snout, and are typically found in freshwater habitats. Crocodiles, on the other hand, are rare and secretive creatures that inhabit coastal, brackish, and salt-water habitats.
Although American crocodiles have an aggressive reputation thanks to the larger, man-eating crocodiles found in Australia, those inhabiting the Everglades rarely come in conflict with humans because of their shy nature.
Crocodiles rely on external sources of heat to regulate their body temperature by basking in the sun or by moving to an area with warmer or cooler water and if surprised by an approaching person they will quickly and noisily enter the water. Crocodiles normally slip quietly the water quietly and splashing indicates it is frightened and feeling stressed.
Crocodiles sometimes can be seen sunning with their mouths open. This behavior is also a way of regulating body temperature and does not mean that the crocodile is acting aggressively toward people.
Crocodiles will eat almost anything that moves. Young crocodiles eat small fish, snails, crustaceans, and insects while adults feed mostly at night on fish, crabs, turtles, snakes, and small mammals. The growth rate of crocodiles varies with food availability and temperature. Digestion is efficient only within a certain range of body temperatures and as a result, crocodiles grow more slowly near the extreme limits of their range.
American crocodiles build nests that are either holes in or mounds of sand and other earthen material. Curiously, the sex of embryos is not determined at fertilization, but by the temperature at which the eggs are incubated. Temperatures of 88 to 91 degrees Fahrenheit produce mostly males and temperatures lower than 88 degrees result in mostly females. However, the temperature must remain above 82 degrees for the eggs to survive and hatch.
Crocodiles nests are on elevated, well-drained sites so that the eggs will be above the high-water mark because crocodile eggs cannot survive flooding for more than 12 hours. Crocodiles typically live to an age of 50 to 70 in the wild.
Although adult crocodiles have no natural predators other than humans, hatchlings have a high mortality rate and are preyed upon by other wildlife including raccoons, birds, and crabs. Alteration of salinity and water levels in Florida Bay resulting from extensive drainage programs throughout south Florida also are a factor. Crocodile nests that are too wet or too dry result in egg mortality. Suitable year-round crocodile habitat was lost with the development of the upper Florida Keys.
There may be a new invasive species. At least two Nile crocodiles have been captured in South Florida and there could be more. A team of researchers used DNA analysis on four crocodiles captured between 2000 and 2014 to confirm that at least two of the crocs were most closely related to Nile crocodiles from Africa.
While Florida is no stranger to non-native amphibians and reptiles, (the Burmese python), the Nile crocodile is a cause of concern because researchers estimate that the croc, an aggressive species, may be responsible for some 200 human deaths a year in Africa. The Nile crocs also have a hearty appetite for cattle and there is concern that there could be potential crossbreeding with American alligators.
Researchers aren't sure how the animals came to be in Florida. But their DNA did not match those kept at Disney’s Animal Kingdom or other facilities that are licensed to keep Nile crocs in Florida. The most likely culprit is an unregistered breeder who brought the crocs to Florida and they escaped of were deliberately released.
The concern is that there are likely more Nile crocodiles lurking in the Florida. This may, or may not be a problem. All one has to do is think of the Burmese python which have now established themselves in the Everglades.