In the vast and diverse animal kingdom, a fascinating group thrives on a diet primarily consisting of insects. These creatures, known as insectivores, play a crucial role in maintaining ecological balance by controlling insect populations. From the depths of the rainforest to the familiar landscapes of our backyards, insectivores exhibit a remarkable range of adaptations and behaviors that enable them to efficiently hunt and consume their tiny prey. This article delves into the world of insectivores, exploring their diversity, dietary habits, hunting strategies, and ecological significance.
What is an Insectivore?
Insectivores are animals that primarily consume insects. Insects are high in protein and fat, which makes them a good source of nutrition for insectivores. While the term "insectivore" might suggest an exclusive diet of insects, it's more accurate to consider insects as a significant proportion of their food intake. Many insectivores supplement their diet with other invertebrates, plant matter, or even small vertebrates.
Diversity of Insectivores
Insectivores can be found across various animal classes, including mammals, birds, amphibians, reptiles, and even spiders. Each type of insectivore has evolved unique strategies for hunting and consuming insects, reflecting the diverse environments they inhabit.
Mammalian Insectivores
There are around 345 mammal species that are insectivores. Most have long snouts, small eyes and very sharp teeth. The order Insectivora comprises a very diverse range of mammals, including shrews, desmans, moles, tenrecs and hedgehogs. Mammalian Insectivores include Shrews, Moles, Hedgehogs and the Xenarthran group which includes the Anteater, Sloth and Armadillo.
Shrews: Shrews occupy the same niche as the earliest insectivorous mammals - small and ground-dwelling, feeding on insects in leaf litter and undergrowth.
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Moles: Moles and golden moles occupy burrowing niches, hunting insects and other invertebrates, such as worms, below the ground.
Hedgehogs: Hedgehogs are not exclusively insectivores but are almost omnivorous. Hedgehogs feed on insects, snails, frogs and toads, caterpillars, worms, beetles, snakes, bird eggs, carrion, mushrooms, grass roots, berries, melons and watermelons. It’s favourite food is slugs and worms, they may eat 40 or more slugs in a night.
Anteaters: Anteaters belong to the order ‘Pilosa’ which also includes Sloths. The Giant Anteater is the largest of the Anteater species, hence its name. Other Anteater species include the Silky Anteater (Cyclopes didactylus) and the Collared Anteater (Tamandua tetradactyla). Giant Anteaters can be found in forests and savannas throughout Central and South America from Belize to Northern Argentina but are more common in the South.
Armadillos: This little armadillo of the forests and grasslands of Central America and northern South America uses an enlarged middle claw of its front feet to tear open ant and termite mounds. These armored ground mammals have big appetites! They need a lot of sustenance from a steady source of insect nutrition. They twist their bodies around to drive those front foot claws deep into the earth.
Sloths: Sloths are omnivores. They may eat insects, small lizards and carrion, however, their diet consists mostly of buds, tender shoots and leaves (including leaves from the cecropia tree).
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Numbats: The numbat has 52 teeth, the most of any terrestrial mammal. Interestingly, it does not really use those teeth to chew its favorite meal, termites. Like the anteater, armadillo, and pangolin, the numbat has a long, sticky tongue to insert into the nests of its prey.
Aardwolfs: This aardwolf skull exhibits greatly reduced molars and carnassials teeth as they are unnecessary for any large, insectivorous animal subsisting on soft insects such as termites.
Elephant Shrews: Elephant shrews are primarily insectivores and eat ants, termites, earthworms, spiders, centipedes, and millipedes. However, they will also sometimes eat leaves, fruits, and seeds.
Pangolins: Pangolins operate much the same way as armadillos and anteaters, but they are not related. Found in Africa and southern Asia, they are toothless and collect ants, termites, and larvae with their tongue.
Avian Insectivores
Birds are essential to reduce the general insect population. In populated areas, birds search high and low (literally) for the perfect insects. They’ll visit yards, gardens, dirt patches, fields, grass, trees, and leaf piles in pursuit of bugs. Many birds even snatch flying bugs right out of the air! Birds prefer to be near fresh water as well, so they often find bugs that visit the same water source.
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- Australian Swiftlet: The Australian Swiftlet (Aerodramus terraereginae) is an insectivore and a flight feeder who preys on insects and floating spiders. It typically feeds during the day and within 30 kilometres of the breeding colony, returning to the caves at night to roost.
Amphibian Insectivores
Common Frog: Common Frogs will feed on any invertebrate of a suitable size. Snails, slugs, worms, beetles, woodlice and flies are all flicked into the frogs wide mouth by its long tongue. The frogs hunt/catch these animals by catching them on their long, sticky tongues. The diets of Common Frogs change significantly throughout their lives, the oldest frogs will feed only on land, younger frogs will also feed in the water.
Spring Peeper: Not all toads and frogs are strictly entomophagous, but the spring peeper is. At only 1.5 inches in length, this little chorus frog found in the wet places of eastern North America is too small to take slugs, small birds, bats, small reptiles, small rodents, or even other frogs like larger and more aggressive anurans.
Reptilian Insectivores
Lizards: Lizards typically feed on insects, birds or rodents. A few species are omnivorous or herbivorous. One familiar example of a herbivorous lizard is the iguana, which is unable to properly digest animal protein. Most lizards eat insects.
Texas Horned Lizard: This lizard of the desert and semi-desert has been found as far to the north as Michigan and as far to the east as Washington D.C. This insectivore is a specialist in harvester ants but will take other insects if it must.
Arachnid Insectivores
Wolf Spider: Wolf spiders are insectivores and eat mostly ground-dwelling insects and other spiders, such as grasshoppers, ants and beetles. Less commonly they will eat small reptiles and amphibians.
House Centipede: The House Centipede (Scutigera coleoptrata) is an insectivore that kills and eats insects. House centipedes feed on bedbugs, termites, cockroaches, silverfish, spiders and other household pests. They kill their prey by injecting venom through their fangs and then eating the dead prey.
Other Insectivores
Archerfish: Speaking of archerfish, this animal, also called the rifle fish has a diet made up mostly of insects. It really does spot an insect on an overhanging branch or leaf and spits water at it from as far as 4 feet away. The insect is then knocked into the water. The banded archerfish is found in the mangrove swamps of Oceania.
Dragonfly: The dragonfly’s wings are powerful and allow it to change direction instantly, fly backward, forward, up, down, left, and right. A dragonfly can hover or can fly as fast as 22 to 34 miles per hour. Its eyesight is acute, and it instantly snatches insect prey out of the air.
Specialized Adaptations for Insectivory
Insectivores have evolved a variety of specialized adaptations that enable them to efficiently locate, capture, and consume insects. These adaptations can be broadly categorized into:
Sensory Adaptations: Many insectivores have highly developed senses that help them locate insects. For example, bats use echolocation to detect insects in the dark, while anteaters rely on their keen sense of smell to find ant and termite colonies. Elephant shrews have a very good sense of smell and excellent sight and hearing, all of which help them when hunting.
Feeding Adaptations: Insectivores often possess specialized mouthparts and digestive systems that are adapted for consuming insects. Anteaters have long, sticky tongues that they use to lap up ants and termites, while some lizards have sticky tongues for capturing insects.
- The anteater has huge salivary glands that produce large amounts of sticky saliva to the tongue which allows many ants, termites and their eggs to stick to it at one time. The tongues microscopic spine-like protrusions further aid the eating process. Its tongue can extend up to 2 feet in length and can be flicked in and out of the insects nest twice a second. As many as 30,000 - 35,000 ants can be consumed in one day.
Locomotory Adaptations: Some insectivores have developed specialized forms of locomotion that aid in their insect-hunting endeavors. For example, the Australian Swiftlet is a flight feeder who preys on insects and floating spiders.
Hunting Strategies of Insectivores
Insectivores employ a wide range of hunting strategies to capture their insect prey. These strategies can be broadly classified into:
Active Hunting: Some insectivores actively search for insects, using their senses to locate and pursue their prey. Wolf spiders chase down and grab their prey, while others wait for it to walk by and ambush it.
Ambush Predation: Other insectivores rely on ambush predation, lying in wait for insects to come within striking distance. Frogs wait until the insect gets just close enough, then zip! The frog’s long tongue shoots out of its gaping mouth and grabs the bug before the insect knows what happened.
Trapping: Some insectivores use traps to capture insects. Spiders that spin webs wait for insects to bumble into the stickier strands. One family of truly innovative spiders, the Deinopidae, use nets to catch insects.
Ecological Significance of Insectivores
Insectivores play a vital role in maintaining the balance of ecosystems by controlling insect populations. By preying on insects, they help to prevent outbreaks that could damage crops, forests, or other valuable resources. Insectivores also serve as a food source for larger animals, contributing to the flow of energy through the food web.
Insectivores in Captivity
Zoos often house a variety of insectivorous animals, providing them with carefully calculated diets to ensure their health and well-being. The Zoo’s insectivores consume a mind-boggling number of bugs each week: 121,000 crickets, 150,000 mealworms and 17,000 waxworms, not including thousands of other non-insect invertebrates, like earthworms and springtails. Insects provide a great source of protein and calcium, which animals need to stay healthy. Keepers provide these colonies with essentially the same levels of care as with any other animal. Staff also make sure the insects are packed with high-quality food, so they have higher nutritional value. Dietary plans are carefully calculated by Department of Nutrition staff. By examining what each animal consumes in its natural environment, the team figures out how to most closely match that diet in the Zoo.