Anteaters are native to Central and South America, inhabiting both forest and open-plain regions. The giant anteater, shown here, is the largest of the species, weighing up to 23 kg (50 lb). The animal is well-adapted to hunt for insects, its sole source of food, because of its long front claws and sticky tongue, which can extend to 60 cm (24 in).
Most predators hunt the largest animals that they can catch without putting themselves unduly at risk. However, some animals concentrate on food items that are much too small to be worth collecting one by one. Instead of catching food individually, they have special feeding adaptations for sweeping it up in bulk.
Strictly a filter feeder, the whale shark strains plankton and small fish from the upper waters of tropical and subtropical seas by lying motionless beneath the water’s surface. Considered the largest living species of fish, a whale shark may measure more than 15 m (50 ft) in length and weigh more than 18 metric tons. The whale shark poses little risk to humans; however, whale sharks have been known to ram boats that they have mistaken for rival sharks.
On land, these animals include insect-eating mammals, such as anteaters and pangolins. Using their long and sticky tongues, they lick up ants and termites and can consume over 20,000 insects a day. In water, this kind of feeding strategy is mirrored by animals called filter feeders, which sieve small animals or food particles from their surroundings. Many of these filter feeders are sessile animals that sieve food from the water immediately around them. Others, such as some whales, scoop up their food while on the move and filter it out in their mouths, using specialized gills or plates of a fibrous material called baleen. This feeding technique is extremely efficient, allowing whales to grow to an immense size.
There are approximately 2,000 species of mosquitoes ranging from the tropics to the Arctic Circle and from sea level to mountaintops. All mosquitoes belong to the insect order Diptera, which includes all of the flies, or two-winged insects. All species of Dipterans have a single pair of wings for flying and a second vestigial pair called halteres, which act as organs of balance. Female mosquitoes have hypodermic mouthparts which enable them to pierce the skin and suck the blood of mammals, birds, reptiles, and other arthropods. The males have reduced mouthparts and feed instead on nectar and water.
In another feeding technique, predators seek out sources of food that are much larger than themselves but only eat part of their prey—usually its blood. This way of life is has been pursued with great success by several groups of flying insects, such as mosquitoes and horseflies. But in the animal world as a whole, fluid diets are much more common in animals that feed on plants. Aphids, cicadas, and other true bugs use piercing mouthparts to suck sap from plant stems. Many different animals, including moths, butterflies, hummingbirds, and bats, use probing beaks and tongues to reach nectar in flowers.
Flukes of the genus Schistosoma parasitize two hosts. The young hatch from their eggs in rivers and lakes and enter a specific kind of aquatic snail, where they develop into tadpole-like larvae called cercariae. When the cercariae leave the snail, they burrow through the skin of a human host swimming or wading in infested water. Adult flukes mature in the host’s bloodstream and settle in the veins of the gut. Their eggs, deposited in the lining of the human intestine and bladder, pass back into water via the sewage system, and the cycle begins again. More than 200 million people worldwide suffer from schistosomiasis, a disease characterized by the abscesses and bleeding caused by the flukes’ infestation.
To avoid the need to track down food, some animals use a highly specialized feeding strategy, called parasitism (see Parasite). A parasite lives on or inside other animals and simply siphons off some of its host's food or, more commonly, feeds on the host itself. External parasites, such as fleas, have well-developed senses and adaptations that enable them to cling to their hosts. Internal parasites, such as tapeworms and liver flukes, are highly modified for a life inside their hosts. The sense organs of internal parasites are rudimentary or absent because they do not need to find food or avoid enemies. Instead, they devote their time entirely to the twin tasks of feeding and reproduction.