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BEETLES (Part 1 of 2)   Leave a comment


Giraffe beetle. Also Giraffe weevil.

DEFINITION:1 any of a large order (Coleoptera) of insects, including weevils, with biting mouth parts and hard front wings (elytra ) that cover the membranous hind wings when the hind wings are folded 2 any insect resembling a beetle.

There are more species of beetles than of any other kind of insect. They constitute the largest order of insects Coleoptera which includes almost one third of a million recognized species. About 20 percent of all known species of animals in the world are beetles.

Beetles are found throughout all continents except Antarctica. Although most species are terrestrial, many such as the whirligig, water scavenger, and true water beetles have become adapted to aquatic environments. Some beetles are only about 0.01 inch (0.025 centimetre) long, whereas tropical rhinoceros beetles and Goliath beetles may reach lengths of 4 to 6 inches (10 to 15 centimetres).

Beetles display a remarkable array of colours, forms, and habits. Some are plain black or have brownish patterns that help to camouflage the insects against certain types of wood or soil. Some beetles are brilliant orange, red, or yellow; others are iridescent green or blue or have a metallic sheen. The antennae of some beetles are large and ornate. Some stag beetles have enlarged, hooked mandibles, or lower jaws, that are almost as long as the beetle itself. Male rhinoceros beetles have huge horns projecting over their heads. The shapes of beetles’ bodies vary from round to elongate. Some are flattened; others are domed or cylindrical.

Some beetles are of great significance to humans. Members of the family of beetles known as weevils, or snout beetles, are notorious agricultural pests. They have specialized, elongated heads and down-curved snouts with mouth parts at the end. Some beetles feed on plant materials such as wood, paper, and fabrics. The larvae of some dermestid beetles are destructive pests of clothing and carpets and even of plant and animal specimens in museums.

Many beetles are valuable because they prey on destructive insect pests. Ladybugs, for example, destroy untold numbers of aphids each year and so protect a wide variety of flowers and vegetables. Many other beetles play more subtle but equally important roles in various ecosystems. Dung beetles, or tumble bugs, eat vast quantities of dung in livestock areas. Carrion beetles are scavengers whose larvae feed on dead animals. Many beetles pollinate flowers.

Physical Characteristics

Mandible, from Latin mandere, to chew; term applied to: (1) chewing jaws of insects and other arthropods; (2) the lower jawbone of mammals; (3) the upper or lower part of a bird’s beak.

Like other insects, beetles have three major body segments: the head, with a single pair of antennae and a pair of compound eyes; the thorax, which bears two pairs of wings and three pairs of legs; and the abdomen, where the reproductive organs are housed. Beetles have chewing jaws called mandibles and paired structures known as maxillary and labial palpi (singular, palpus) that are used for feeding or handling food. The bodies of beetles and other insects are covered by a usually hard layer known as the cuticle that supports the internal organs and protects the body. The cuticle is hard because it contains a substance called chitin. Each defined, plate like area of the cuticle is called a sclerite.

A distinctive feature of beetles is their front pair of wings, which are thick, hard, and opaque, without the veins characteristic of most other insect wings. These fore wings, called elytra (singular, elytron), serve as protective wing covers for a second pair of functional wings underneath. The hind wings are membranous and translucent. These are ordinarily used for flying, while the heavy elytra are held out of the way. When the beetle is at rest, the elytra fold over the back and form a straight line down the centre where they meet. Some beetles have shortened wings, and a few species are entirely wingless.

Life Cycle and Behaviour

Like other insects, beetles reproduce sexually by means of internal fertilization. The ovaries of the female and testes of the male are enclosed within the abdomen. In some species, such as the stag beetles, males engage in combat with one another for the right to mate with the females. After mating, the females lay the fertilized eggs in a location suitable for development of the larvae.

Beetles undergo a complete metamorphosis: they develop from egg into active larva into inactive pupa and finally into an adult. The larva, or grub, does not resemble the adult in structure. The pupal stage though soft, pale, and immobile does have the body form of an adult. The life spans of beetles range from a few months in some species to more than four years in others.

Feeding habits. Most beetles feed on living or dead plant materials, but some are scavengers of dead animal matter and some prey on other insects. A few are parasites.

The adults and larvae of a number of beetle species feed on various plant roots, stems, fruits, seeds, and foliage. Some beetles feed only on certain plant species and plant parts, whereas others are less particular in their choice of foods. The adults and larvae of many beetles feed on decaying wood and help break down dead trees and other vegetation in forest habitats.

Some beetles, such as tiger beetles, are voracious predators. Adult tiger beetles search for prey that they can subdue with their powerful mandibles. The larvae are sedentary; they live in small tunnels where they wait to capture passing insects. Water scavenger beetles are predators as larvae but are plant eaters as adults. Some species of beetles have highly selective feeding habits: they may eat only mites, ant larvae, aphids, or zoo plankton

Defences Although most beetles are protected by their heavy armour, some species have developed additional methods of defence Blister beetles secrete an oily, blister-causing substance that deters predators. Beetles may also discourage or avoid predators by making a startling noise (see below, “Light and sound production”), secreting or ejecting an obnoxious fluid, biting, hiding (using their natural colouring as camouflage), or simply fleeing on foot or on wing.

Luminescence, emission of light resulting from causes other than high temperature.

Light and sound production. Many beetles are capable of producing light and sound, primarily for the purposes of attracting a mate or for frightening enemies. The familiar fireflies, or lightning bugs, are beetles that have special light organs on the underside of their abdomens. These beetles usually the males flash their lights rhythmically as a signal that they are ready to mate, and the females return the signal. The kind of signal system used by the two fireflies allows males and females of the same species to recognize and locate one another. Some tropical click beetles have large, luminescent eye spots on the back of the thorax that presumably are also used in courtship.

Many species of beetles make sounds by rubbing together hard parts of their bodies a practice called stridulation. The vibration created by the friction of these parts produces a shrill creaking noise. Beetles may stridulate by rubbing the two elytra together, by rubbing a hind leg against an elytron, or by rubbing the head against the front of the thorax. In some species, even the immature grubs can produce sounds. Although stridulation is often used by adult beetles as a mating signal, its purposes in other instances by juveniles, for example are not fully understood.

A wood-boring beetle known as the death-watch beetle strikes its head against the sides of its burrow as a mating signal. The name death-watch is derived from the superstition that the sound was an omen of death. One explanation is that the ticking sound of a death-watch beetle that had made its burrow in an old piece of furniture was most often heard late at night by someone sitting at a sickbed.

When threatened by a predator, bombardier beetles squirt, with a loud popping sound, an unpleasant-smelling liquid from the rear of their abdomens. The noise and the ejection act together to startle and repel the predator and give the beetle time to make its escape. When click beetles fall on their backs, they right themselves by snapping their bodies in such a way that they are tossed into the air with a loud clicking sound that can startle a predator.

Kinds of Beetles

There are many families of beetles about 135, according to some experts. The beetles discussed below represent a sampling of some of the most commonly known as well as some of the most unusual beetle families in the order Coleoptera.

Tiger beetles and ground beetles are the most common beetles in North America. The fierce, long-legged tiger beetles are fast-running, fast-flying, often brightly coloured beetles that capture and eat other insects. Species of tiger beetles occur throughout the world but are especially abundant in the tropics.

Ground beetle, one of a group of the order Coleoptera, family Carabidae; especially the fiery searcher (Calosoma scrutator), one of the largest beetles; if held carelessly will discharge quantities of “fiery” juice.

Ground beetles are also abundant in most parts of the world. Many species are black and shiny; some are iridescent. Like the tiger beetles, ground beetles have long legs. Some have enlarged, pinching mandibles that are used to capture prey. Many are nocturnal.

True water beetles (also known as diving beetles or predaceous diving beetles) are oval-shaped insects that can swim, dive, and fly. They are found in most freshwater habitats worldwide but are most common in northern temperate regions. The hind pair of legs of the true water beetle are long, flattened, and fringed to provide a greater surface area that helps the insect float. The beetle breathes through spiracles openings on the abdomen just under the tips of the elytra. Before diving, the beetle collects an air bubble beneath its elytra and then breathes from the bubble while it is underwater. It is carnivorous, preying on insects and other aquatic organisms, including fish larger than itself. The larvae of the true water beetles are sometimes called water tigers because of their voracious appetites. True water beetles often fly from one aquatic habitat to another and may be seen around outdoor lights at night.

Whirligig beetles, like the true water beetles, are oval-shaped aquatic predators that can swim, dive, and fly. They are known for their gregarious habits they are usually seen in groups, spinning and whirling around on the surfaces of quiet ponds or lakes. They have distinctive, divided eyes a top pair for seeing above the water’s surface and a bottom pair for seeing below.

Posted 2012/01/25 by Stelios in Education

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BEETLES (Part 2 of 2)   Leave a comment

Water scavenger beetles include more than 1,000 species of primarily tropical aquatic beetles, with approximately 200 species native to North America. Like the true water beetles, water scavenger beetles must find a way of supplying themselves with oxygen while they forage underwater. At the water’s surface, the beetles project their antennae out of the water to capture a bubble of air. Then they place the bubble beneath their bodies to breathe from it as they swim. This bubble makes water scavenger beetles look as though they have a silvery film on their undersides.

Carrion beetles and burying beetles are widely distributed and eat primarily dead animal matter. Many carrion beetles are relatively large and brightly coloured Burying beetles are so named because they dig beneath small dead animals such as rodents, birds, and reptiles until the animal is completely buried beneath the soil. Then the female digs her way down to the carcass and deposits her eggs. Upon hatching, the larvae feed on the body of the dead animal.

Rove beetles have short elytra that do not cover the abdomen. When they are being pursued, rove beetles run with the tip of their abdomens curled over their backs, giving their abdomens the appearance of stingers. One species expels a fluid from the tip of its abdomen that repels attacking ants.

Luminescence, emission of light resulting from causes other than high temperature.

Fireflies are soft-bodied beetles, most of which produce light in special organs located in the undersides of their abdomens. The light is produced by a chemical reaction between oxygen in the air and two chemicals in the firefly’s body. The females of most species have short wings or are wingless. The wingless females and most firefly larvae are often called glow worms Some species in the firefly family do not produce light.

Stag beetles are best known for their enormous, distinctive mandibles. These are most pronounced in the males. Stag beetles are often found in and around rotting logs, on which the larvae feed. Adults are often attracted to outdoor lights.

Scarab beetles include a wide variety of species about 20,000 worldwide. More than 1,300 species occur in North America. Most scarab beetles are stout and robust, but their size varies greatly from one species to another. Some small species are about 0.08 inch (0.2 centimetre) in length, whereas some of the tropical species are the largest beetles in the world up to 6 inches (15 centimetres) in length. Some members of the scarab-beetle family are scavengers: both the larvae and the adults feed on dung and carrion. Others are plant eaters: the larvae eat roots or wood and the adults eat leaves and flowers. Many members of the latter group are agricultural pests. June bugs and May beetles are scarabs.

Click beetles are small to medium-sized beetles with elongated, flattened bodies that have bluntly rounded ends. The largest species reach lengths of about 2 inches (5 centimetres). The larvae of click beetles, called wire worms, cause extensive crop damage in some areas because they feed on underground roots, seeds, and stems.

Metallic wood-boring beetles resemble click beetles in general shape but can be distinguished by their bright metallic colours Some species damage orchards and forests.

Dermestid beetles are mostly small, scavenging beetles. In the household they are particularly harmful to stored foods, leather, furs, and wool products. Although the adults and larvae are scavengers, most of the damage is done by larvae.

Ladybugs, with their roundish, brightly coloured bodies, are the favourite insects of many people. The adults and larvae are often predators of other invertebrates that are agricultural or garden pests, and many fruit growers consider ladybugs to be among the most beneficial of insects.

Darkling beetle, any beetle of the family Tenebrionidae, which includes meal worms, flour beetles, and other species occurring under stones, in dead wood, fungi, and dry vegetable products; most are black or brown.

Darkling beetles include about 15,000 species worldwide. Of the more than 1,400 species in the United States, most are found in the arid South west Most darkling beetles are solid dull black in colour Meal worms are actually the larvae of darkling beetles. Although they are major pests of grain products, meal worms are also commonly raised as food for insect-eating animals such as lizards, frogs, and birds.

Cantharidin, blistering substance obtained from Spanish-fly beetle and other insects of same family.

Blister beetles are elongate, relatively soft-bodied beetles. The adults of most species feed on plants. Blister beetles secrete an irritant called cantharidin. The substance has been used to produce a drug that causes a blistering reaction on the skin most often as a topical skin irritant to remove warts. The substance was first extracted from a bright green blister beetle of southern Europe known as Spanish fly. The drug, also called Spanish fly, was once considered an aphrodisiac, but it can be toxic if taken internally.

Long-horned, wood-boring beetles are often medium-sized to large 0.8 to 2.4 inches (2 to 6.1 centimetres) in length with extremely long antennae. The larvae of these beetles are usually wood-borers that feed on a variety of trees and can cause considerable damage. More than 20,000 species have been described worldwide, and at least 1,200 of these are native to North America. Some are brightly coloured and metallic in appearance.

Leaf beetles are abundant and widely distributed. They are relatively small, and many are brightly coloured and resemble ladybugs. The adults and larvae feed on foliage and also on other plant parts.

Engraver beetle, any of numerous beetles of family Scolytidae; most live under bark of trees and engrave the wood by burrowing.

Bark beetles are considered the most destructive insects of temperate-zone forests. Both the adults and the larvae live beneath the bark of trees. The damage they inflict on the tree depends on the species. Engraver beetles, for example, feed on the inside of the bark and on the surface of the trunk. Other bark beetles bore directly into the trunk and feed on the wood. Ambrosia beetles bore into the tree’s trunk and feed on fungi that live there. Members of the bark-beetle family are dark-coloured. Their antennae are elbowed and have an enlarged, club like end.

Weevils, or snout beetles, constitute an abundant and diverse beetle family with more than 40 subfamilies and 40,000 recognized species. Their most characteristic feature is the beak or snout. It is well-developed, curves downward, and in some species may be twice as long as the body. The snout is used not only for penetration and feeding but also for boring holes in which to lay eggs. The weevils’ antennae are elbowed and club-shaped at the end. Many weevils have no wings; others are excellent fliers. Most are less than 0.25 inch (6 millimetres) in length and are plainly coloured and marked, yet the largest exceed 3 inches (80 millimetres) in length and may be brightly coloured This family includes some extremely destructive pests, such as the grain weevil and the rice weevil.


Taxonomists divide the Coleoptera into two or more suborders, depending on the classification scheme they prefer. The two suborders common to most schemes are Adephaga and Polyphaga. The suborder Adephaga consists of several families of beetles that are mostly predaceous, including the tiger beetles and ground beetles, the true water beetles, and the whirligig beetles. The suborder Polyphaga contains the majority of beetles.

Tiger beetles and ground beetles belong to the family Carabidae, which contains the largest number of beetle species in North America. (Some taxonomists place tiger beetles in a separate family, Cicindelidae.) Bombardier beetles are also members of the Carabidae family. The true water beetles are in the family Dytiscidae, whirligig beetles are in Gyrinidae, and water scavenger beetles are in Hydrophilidae. Carrion beetles and burying beetles belong to the family Silphidae. Rove beetles are in the family Staphylinidae and have almost as many species in North America as does the family Carabidae. Fireflies and glow worms belong to the family Lampyridae. Stag beetles are in the family Lucanidae. Scarab beetles belong to the family Scarabaeidae, which includes the rhinoceros beetles, Goliath beetles, and dung beetles. Click beetles are in the family Elateridae. Metallic wood-boring beetles are placed in the family Buprestidae. Dermestid beetles belong to the family Dermestidae, and ladybugs are in the family Coccinellidae. Darkling beetles are in the family Tenebrionidae. Blister beetles belong to the family Meloidae. The long-horned wood-boring beetles are classified in the family Cerambycidae, and leaf beetles are placed in the family Chrysomelidae. Bark beetles belong to the family Scolytidae. Weevils belong to the largest family of beetles in the beetle order the family Curculionidae. Bess-bugs belong to the family Passalidae. The death watch beetle is in the family Anobiidae.

Assisted by J. Whitfield Gibbons, Senior Research Ecologist and Professor of Zoology, Savannah River Ecology Laboratory, University of Georgia.

Posted 2012/01/25 by Stelios in Education

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