Scavengers (zoology)

Carnivorous worms, bears, beetles, kites, vultures, gulls, and hyenas do not live only by killing prey. To varying extents, they eat scraps from other predator kills and the corpses of animals that died of old age, injury, or illness. Contrary to popular belief, many scavengers are poorly designed for hunting. Some have short talons, lack optimum teeth, or lack the tact and coordination to properly catch prey. Regardless, they are ecologically important as they ensure that carrion does not become breeding places for disease organisms.

All scavengers have a keen sense of smell to help them to find decaying flesh. They need not worry about corpses fighting back, although they do risk contracting dangerous diseases. However, scavengers rarely die from eating carrion because natural selection has given them tolerance of foods that kill other animals.

Scavenger Worms, Beetles, and Maggots

The sea mouse is a segmented worm related to earthworms. An undersea scavenger, it lives in shallow coastal waters worldwide. In a sea mouse, each body segment is separated from the others by chitinous tissues. On the sides of the segments are muscular protrusions having bristly hairs used in locomotion. Finer hairs growing from the segments allow the worm to sense its surroundings. As a sea mouse crawls through the seabed, it eats carrion. The worm has a flat, three-inch wide, nine-inch-long body. Scales and bristles, like gray fur, cover it and lead to the name sea mouse.

Scarab beetles are one of the twelve thousand species of colorful beetles, which grow up to six inches long. They have horns on their heads or thoraxes. Males use the horns in combat during mating. Many beetles eat carrion. Dung beetles are most often called scarabs. Some scarabs (tumble bugs) form dung into balls and roll it into their burrows. There it becomes food for them or for their larvae, hatched from eggs deposited on the pellets. Ancient Egyptians worshiped tumble bugs, viewing the dung pellets as symbolizing the world and the scarab horns as symbolizing the sun’s rays. Thinking that scarabs caused good fortune and immortality, they used scarab carvings as charms and replaced the hearts of the embalmed dead with carved scarabs.

Maggots, the larva of flies, are tiny yellowish-brown, worm-like creatures that feed on decaying organic matter, including carcasses. Their oversized salivary glands allow them to digest this matter more easily. Though all maggots survive on consumption of decomposing matter, their general food preferences can differ depending on their genus and species. For example, while some species feed almost solely on decaying carcasses, such as maggots of the green bottle fly (Lucilia sericata), others prefer grains, like seedcorn maggots (Deltia platura). Though they are often regarded as vile creatures, maggots perform a necessary process for decomposition that aids in plant growth and the breakdown of rotting matter.

Bears, Jackals, Raccoons, and Hyenas

Many mammals, such as bears, jackals, hyenas, and raccoons, are scavengers only when necessary. Among bears, the best-known scavenger is the American black bear. It averages six feet long, approximately three feet tall at the shoulder, and weighs three hundred pounds, which is small and light for a bear. This small size may make it unable to compete for choice bear fare and explain why black bears eat carrion. Given the option, black bears prefer twigs, leaves, fruit, nuts, corn, berries, fish, insects, beehives, and honey.

Raccoons, nocturnal animals, inhabit swamps or woods near water. They eat frogs, crayfish, fish, birds, eggs, fruits, nuts, rodents, insects, and carrion. Raccoons have stout, catlike bodies, masked faces, coarse yellow-gray to brown fur, body lengths up to two feet, and ringed, bushy tails, and weigh up to fifteen pounds. They are solitary except for mating in January and February. After two-month pregnancies, females give birth to three to seven babies, which remain with them for a year. Wild raccoons live for up to seven years.

Jackals are Old World wild dog scavengers that live on plains, deserts, and prairies. Golden jackals live from North Africa to southeast Europe and India. Black-backed jackals inhabit East and South Africa. Jackals have foxlike heads but otherwise resemble wolves. They are nocturnal creatures, holing up in dens during the day. They eat carrion and small birds and mammals, hunting in packs. Jackals live for up to fifteen years.

African and Asian hyenas are also built something like wolves. The two main species, spotted (laughing) hyenas and striped hyenas, were once thought to eat only carrion. This notion arose from observations of their carrion-eating and because hyena hind legs, shorter than their front legs, make them look awkward.

African laughing hyenas have brown fur liberally sprinkled with spots, large heads, and jaws and teeth that can crush bones. These hyenas, six feet long and three feet tall at the shoulder, are less clumsy than they look. It is now thought that they are the greatest killers of zebras. Nocturnal hyena packs kill prey or eat carrion. Hyenas live in groups of about sixty members. Females have one or two cubs after four-month pregnancies. Little is known about striped hyenas, which are smaller and less aggressive. They are tan, with dark, vertical stripes and live from East Africa to Asia. Hyenas live for up to twenty-five years.

Scavenger Birds

Kites, one bird scavenger group, are hawks found in warm parts of all continents. Their legs and feet are small and weak, so they eat carrion and small animals. Swallow-tailed kites are two feet long, with beautiful white bodies and black wings and tails. They inhabit the southern United States. The smaller, white-tailed kite inhabits the Americas, Europe, and Asia. Kites often hover in the air, searching for insects and small mammal carrion.

Vultures are larger carrion eaters. New World vultures are related to storks and live in the temperate and tropical regions of the Americas. The Old World vultures of Europe and Asia resemble New World vultures in eating habits but are related to hawks and eagles. Unlike kites, vultures look like carrion eaters. Most are ugly and dark-feathered. They lack plumage on their heads and necks, minimizing messiness from blood and gore. Vultures are predisposed to carrion-eating because they have blunt claws, which are poor weapons for hunting. They are suited to finding carrion by their ability to sustain long flights and their sharp eyes. Vultures fly in flocks, except during mating, when pairs nest on cliffs or in caves. Most vultures lay three eggs among bare rocks. Parents incubate the eggs and feed their young, which can fly when six months old.

There are six New World vulture species. Turkey vultures (buzzards) live in the southern United States and northern Mexico. The largest North American land bird is a vulture, the California condor, which is up to six feet long with a wingspan of up to eleven feet. Andean condors are the largest South American vultures. Condors have black body plumage. The naked heads and necks of vultures and condors vary in color and in the presence or absence of feather ruffs and wattles.

There are fourteen Old World vulture species. Most interesting are the bearded vultures called lammergeiers, four feet long and weighing up to fifteen pounds. They inhabit mountains up to fifteen thousand feet high in Europe, Africa, and Asia. Lammergeiers build nests on ledges or in mountain caves. They have tan chest and stomach plumage, white faces, and dark brown wings and tails. Masklike black feather “beards” surround their eyes and beaks. Also of interest are Egyptian vultures, two feet long, with naked yellow heads, white body feathers, and black wings. They live in Mediterranean areas and as far east as India. Many Old World vultures are not as funereal-looking as the New World breeds.

Gulls, also scavenger birds, are pigeon-sized and long-winged. Most live in the oceans and large inland lakes. Adults have gray plumage on their wings, backs, and heads, webbed feet, and white underparts. They are graceful fliers and swimmers and nest in large colonies on rocky islands or in marshes. Gulls eat fish, other water animals, insects, carrion, garbage, and the eggs or young of other birds.

Best known are white herring gulls. Adults are two feet long, and, in addition to the typical gray and white gull motifs, have black wing tips, yellow bills, and flesh-colored legs. They eat fish, shellfish, garbage, and carrion. Often commercial fishermen, cleaning catches, see gulls swarming behind their boats, awaiting fish offal. Herring gulls mate and lay about six eggs. Females incubate them for three weeks and feed the offspring until, at six weeks old, they strike out on their own.

Sharks

There are over three hundred shark species. They differ from bony fish in having skeletons made of cartilage, not bone. Many sharks eat nearly all large marine animals. They vary from forty to fifty foot long to six-inch-long species. Most abundant in tropical and subtropical waters, nearly all sharks are viewed as aggressive carnivores.

Sharks are usually gray, having leathery skins and gills behind the head. Shark tails are not symmetrical, and shark skeletons end in upper tail lobes. Shark fins and tails are rigid, not erectile, as in bony fish. Sharks also have a keen sense of smell, sensing traces of blood and homing in on their sources. Despite their great strength, sharks are mostly scavengers, eating injured fish and carrion. They also eat seals, whales, and fish.

Benefits of Scavenging

Scavengers consume carrion, preventing its decay and the endangerment of the health of other animals. This is one of their main ecological functions. Species such as the sea mouse, the carrion beetle, maggots, scarabs, vultures, and condors choose to eat carrion. Others, such as American black bears, jackals, raccoons, kites, sharks, and gulls, given a choice, much prefer catching live prey.

Also, some scavengers’ perceived food sources may be based on incomplete data. For example, laughing hyenas were dubbed scavengers based on their awkward appearance and a few observations. More careful study showed that they are more predator than scavenger. In addition, regardless of preference in obtaining their food, scavengers such as sharks and vultures have another important ecological role in the oceans and on land—killing the injured or weak members of other species. This activity helps those species to select strong individuals, enhancing the chances of species survival.

Principal Terms

Carrion: the corpses of dead animals

Cartilage: the wing case of a beetle

Chitinous: made of fibrous chitin

Elytra: the wing case of a beetle

Bibliography

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Le Sage, Mitchell J., et al. "Do Scavengers Prevent or Promote Disease Transmission? The Effect of Invertebrate Scavenging on Ranavirus Transmission." Functional Ecology, vol. 33, no. 7, 2019, pp. 1342-1350. doi.org/10.1111/1365-2435.13335. Accessed 5 Oct. 2024.

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