File Snakes: Acrochordidae

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FILE SNAKES: Acrochordidae

LITTLE FILE SNAKE (Acrochordus granulatus): SPECIES ACCOUNT

PHYSICAL CHARACTERISTICS

Also known as wart snakes or elephant-trunk snakes, the file snakes have baggy skin that lies in loose folds. The skin is covered with tiny scales and small, bristly outgrowths that make the skin seem quite rough. This rough skin looks rather like the surface of a file, and some say it also looks as if it is covered with small warts; it is the appearance of their skin that gives them the common name "file" snakes. Although for many years people thought that the little file snake was venomous (VEH-nuh-mus), or poisonous, and dangerous to humans, scientists now know that none of the three file snake species, or types, has a bite that can harm a person.

File snakes spend nearly their entire lives in the water. A file snake has both its eyes and its nostrils, or nose holes, located on the top of its short head, so it can breathe the air and see above the water surface while the rest of the body remains underwater. The nostrils also have little valves, or flaps, that can close up when the snake dips completely below the water's surface. The tail is somewhat flattened from side to side and helps the snake swim. Male and female file snakes look very much alike, except that the females have slightly larger heads, thicker bodies, and shorter tails. The tail on a snake is the part of the body that extends back from a slit on the belly. File snakes range in length from about 20 to 76 inches (0.5 to 2 meters). The little file snake is the smallest member of the family, averaging 20 to 28 inches (51 to 71 centimeters) in length but sometimes reaching 40 inches (1 meter). The Arafura file snake grows to about 67 inches (1.7 meters), and the Java file snake grows to 76 inches (2 meters).

GEOGRAPHIC RANGE

The file snakes live from India to Southeast Asia and Australia. They inhabit northern Australia, the Solomon Islands east of New Guinea, Malaysia, and Indonesia.

HABITAT

The file snakes usually live in warm, shallow waters. The Arafura and Java file snakes live in freshwater streams; lagoons, or shallow bodies of saltwater near the sea; and rivers. In the dry season, the Arafura file snake is also found in billabongs (BILL-uh-bongs), which are dried-up streambeds. During the rainy season, it will slither into flooded grasslands. The Java file snake, on the other hand, occasionally swims into the salty ocean water for short periods of time. Little file snakes can live in both freshwater and saltwater areas, from the ocean to swamps near the coastline and to inland rivers, sometimes up to 6 miles (9.6 kilometers) out to sea and in water up to 66 feet (20 meters) deep. Little file snakes have salt glands, small groups of cells that may help them control the amount of salt in their bodies. Salt glands are also seen in many other animals that live in salty waters. Scientists have not studied this gland in detail, however, so they are unsure how important it is to the snake's survival in saltwater.

A DIFFERENT WAY TO SHED

A little file snake sheds its skin differently from the typical land-living snake, which turns its skin inside out as it scoots out of the old skin. Instead, the little file snake first wriggles its body free of its loose skin, so that the skin is separate from the body but still in place around it. Then it works its way free, sometimes knotting its body to help it escape from the old skin. The skin remains right side out.

DIET

The three file snake species eat mostly fishes, and they do not seem to care whether the meal is alive or dead when they find it. The little file snake also eats crustaceans (krus-TAY-shuns). Crustaceans include shelled animals, such as shrimp and crayfish. The Java file snake adds freshwater eels to its diet of mainly catfishes. The Arafura file snake can eat very large fishes. According to one report, a snake that measured 44.5 inches (113 centimeters) in length ate a 19-inch-long (48-centimeter-long) fish—nearly half the snake's size—in just two minutes.

BEHAVIOR AND REPRODUCTION

The file snakes rarely leave the water, but they occasionally move from one body of water to another during the wet and dry seasons or when ocean water levels rise and fall due to the tides. During the daytime, they stay among roots, in holes in the muddy water bottom, or in other hiding places and come out to hunt for food at night. Using the bristles in the outgrowths on their skin, file snakes can sense changes in the murky, or dark, water, which helps locate animals that they might otherwise be unable to see. To hunt, a file snake either will strike out and grasp a passing fish with its mouth or will quickly wrap its body around the fish and hold it until the snake can reach around with its head to bite and eat the fish. Unlike constrictor (kun-STRIK-tuhr) snakes that wrap around and squeeze their prey to death before eating it, the file snake coils around the prey only to hold it temporarily until it can quickly gulp it down. Although they can swim quite well, adults usually move slowly along the bottom. Scientists know very little about the behavior of young file snakes.

Java and little file snakes have young every other year, and Arafura file snakes have young even less often. All of the three species lay eggs, probably from the middle of the wet season to late in the wet season. The little file snake has about five eggs at a time, the Arafura file snake has about seventeen, and the Java file snake lays an average of twenty-six eggs. At least among the Arafura file snakes, larger females have a larger number of young.

FILE SNAKES AND PEOPLE

Some people collect file snakes as food and for their skin, which is used for leather. Since the snake reproduces only once every two years, or even less often, such collecting over the years could lead to dangerous drops in the numbers of snakes. People only rarely collect file snakes for the pet trade.

CONSERVATION STATUS

File snakes are not considered threatened, but some populations may have low numbers. Habitat loss, as well as habitat damage from water pollution, or dirtying and poisoning of water, may hurt their ability to survive into the future. In areas with large fish populations, however, file snakes can become very numerous. Scientists have counted 100 or more Arafura file snakes on every 2 acres (0.8 hectare) of some Australian billabongs.

LITTLE FILE SNAKE (Acrochordus granulatus): SPECIES ACCOUNT

Physical characteristics: The little file snake is rough skinned, with a thick body and a small head. Its back is dark brown with yellowish to reddish stripes. It has loose, baggy skin. Little file snakes are the smallest of the three file snake species, at about 20 to 28 inches (51 to 71 centimeters) long.

Geographic range: The little file snake lives from the western coast of India through the tropical regions of Southeast Asia (including Indonesia and the Philippines) to New Guinea and northern Australia.

Habitat: This snake is mainly a saltwater animal, although it can also live in freshwater. It usually is found in shallow water just a few feet deep, but it has also been seen in ocean water up to 6 miles (9.6 kilometers) from shore and 66 feet (20 meters) deep.

Diet: The little file snake eats mainly the spiny-finned fishes called gobies (GO-bees) and other goby-like fishes and crustaceans.

Behavior and reproduction: This snake rarely leaves the water. It can easily stay underwater for two hours and, if necessary, up to five hours at a time. Although it is a very good swimmer, it usually moves slowly along the muddy water bottom. It is active mainly at night, when it hunts for food. These snakes probably mate in the fall. The females lay eggs about once every other year. A typical litter has five eggs, but there may be as few as one egg or as many as twelve. Larger females have larger numbers of young.

Little file snakes and people: Some people hunt little file snakes for their skin, which is used as leather.

Conservation status: The little file snake is not considered to be endangered or threatened. ∎