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Animals/Insects

Home » Animals » Insects » Beetles


Beetles

[Photo of Firebug, Pyrrhocoris apterus]

Firebug

Pyrrhocoris apterus

Beetles are by far the most varied group of all insects. So far, 350,000 species of them have been named, and there may be as many still waiting to be recognized. Beetles constitute 40 percent of all known insect species and 30 percent of the species of all known animals.

The smallest beetle is even smaller than the head of a pin. The biggest, such as the titan beetle that lives in the forests of the upper Amazon, can measure 17.5 cm (over 6 inches) from the tip of its ferocious mandibles to the end of its armored abdomen.

One of the reasons of their success is the structure of their wings. Like the insects that preceded them, they have two pairs. The back two, called are membranous and used in flight. The front pair have been thickened, hardened and converted into covers to protect the hind wings. Hence the scientific name of the whole family - Coleoptera, "shield wings." The fore-wings are called elytra. In flight beetles usually hold up their elytras out of the way of their beating rear wings.

[Photo of Agave Billbug, Scyphophorus acupunctatus]

Agave Billbug

Scyphophorus acupunctatus

With their delicate flying apparatus fully protected, beetles can tackle all kinds of rough tasks. They can dig into the ground and barge their way through rubble. They can bore into wood, tunnel into dung and even, by holding a bubble of air beneath the elytra, swim.1

Life Cycle

Beetles, along with flies, moths, wasps and some other insects, have the most advanced form of metamorphosis, called the complete metamorphosis. Great changes occur during this type of development, which includes four very distinct stages: egg, larva, pupa, and adult.

[Photo of Stink Bug, Brochymena sp.]

Stink Bug

Brochymena sp.

Egg

The eggs are developed in the ovaries of the female and are laid in a sheltered place where the young will have a food supply and favorable conditions for development. Eggs may be laid singly or in masses; hatching usually occurs after several days. The female nearly always goes on her way after egg-laying and leaves the young to care for themselves.

Larva

When the egg hatches, a wormlike stages called the larva emerges. There is no single general term for beetle larvae comparable to term caterpillar for moth and butterfly larvae. Beetle larvae are usually called grubs, but some are called worms. The larvae of different beetles vary greatly in appearance and habits. generally, they have a distinct head with chewing mouth parts.

[Photo of Elephant Stag beetle, Lucanus elephus]

Elephant Stag Beetle

Lucanus elephus

Most larvae have simple eyes called ocelli, others may lack eyes entirely. The skin must be shed periodically to allow for increase in size. This shedding of the skin is called molting. The stages marked by this molting are called instars. The number of instars that the beetle larva passes through varies greatly. Several distinct types of body forms are to be found among beetle larvae:

  • C-shaped (scarabaeiform)
  • Wormlike (vermiform)
  • Flattened and elongated (campodeiform)
  • Wirewormlike (elateriform)
  • Caterpillarlike (eruciform)

Some beetles, especially parasitic species, undergo hypermetamorphosis during their development. This means that the larva exhibits different body shapes as it develops. Most beetle larvae live on land and feed on or within various parts of plants, both above and below ground. Some live on or within decaying vegetation or animal matter. Many larvae prey on other insects, while a few feed on fungi.

[Photo of Spotted Cucumber Beetle, Diabrotica undecimpunctata]

Spotted Cucumber Beetle

Diabrotica undecimpunctata

Pupa

The pupa is called the resting stage. The pupa of most species looks like a pale, mummified adult beetle. In a few species the pupa is covered by a cocoon made by the last instar larva. Within the pupa, larval tissue break down to form adult structures. Most aquatic beetles pupate on the shore in mud, silt, or damp vegetation. One of the few aquatic pupae known among beetles is that of the Water Pennies (Psephenidae); it is oval and flattened like the larva, with tufts of gills on the abdomen, and clings to the rocks. Some Chrysomelids pupate in plant tissues or in gas-filled cocoons attached to plants.1

Adult

Immediately after the pupa molts to form the adult, the beetle is soft-bodied and pale-colored. The hardening of the body and darkening to adult coloration may take many hours. Once the adult exoskeleton hardens, the beetle neither grows nor molts. One generation per year is typical for beetles, but some may have 2 or 3 generations. The adult lives for just a few weeks, but some adults may live for several months.2

[Photo of Tiger Beetle]

Six-spotted Green Tiger Beetle

Cicindela sexguttata
Photo courtesy of biosurvey.ou.edu

Beneficial Beetles

In the Coleoptera man has many good allies. The Ladybird Beetles (Coccinellidae), the Ground Beetles (Carabidae), and the Tiger Beetles (Cicindellidae) are the most conspicuous. But the larvae of many Rove Beetles (Staphylinidae) consume large numbers of Aphids; the larvae of the Checkred Beetles (Cleridae) and of the Fireflies (Lampyridae) do the same. The larvae of some Blister and Oil Beetles (Meloidae) eat the eggs of Grasshoppers.

There are nearly 4,000 species of Ladybirds in the world and about 370 in North America. Very few species are pests, so in general Ladybirds should be protected and encouraged, because in both larva and adult life they rank among our most beneficial insects. The reddish-orange ones, of which we have 40 species, feed primarily on Aphids. The blackish species prefer Scale insects, Mealy bugs, and white flies. When food is scarce they will nibble on plant material, however. Many species will eat only certain stages of these insects, so that not all Ladybirds can be used to control any particular pest.1

Beetle Pests

The most common wood-destroying beetles are found in the families Anobiidae (furniture beetles), Lyctidae (powderpost beetles), and Cerambycidae (longhorn beetles). Among the most common garden pest species are the Japanese beetles, asparagus beetles and rose chafers. Pest beetles chew holes in stems, leaves and flowers during the growing season. The larvae of some species feed on roots. Japanese beetle grubs are a pest of lawns, producing patches of dead or wilted grass. Grain beetles are able to destruct large volumes of stored grains.

Pictured Beetles

Red Bug, Scantius aegyptius - These bugs are not considered to be economically important species; has been observed feeding on the developing seeds and stems of knotweed and malva. It is likely that S. aegyptius will feed on the seeds of several species of annual herbaceous plants.

Agave Billbug, Scyphophorus acupunctatus - Habitat: deserts; adult eats the sap of agave plants; larva feeds on the flower stalks of agave plants; the related Yucca Billbug feeds on yucca plants.

Stink Bug, Brochymena sp. - Habitat: fruit orchards, woods; food sources include juices of caterpillars and other soft insects.

Elephant Stag Beetle, Lucanus elephus - Also called Giant Stag Beetle; habitat: woods; food sources include plant juices and aphid honeydew; larvae eat wet decaying wood.

Spotted Cucumber Beetle, Diabrotica undecimpunctata - One of the most destructive beetles. It damages foliage, flowers, and pollen of cucumbers, melons, corn, potatoes, and peanuts. Female deposits yellow eggs in soil near food plants. Larvae feed on roots and stems until fully grown, then constructs pupal cells below soil.

Six-spotted Green Tiger Beetle, Cicindela sexguttata - Habitat: woodlands; food sources include small insects and spiders.

Threats to Beetles and Their Conservation

Habitat loss is the primary threat to the survival of all beetles. Despite their incredible success, beetle populations are limited, sometimes drastically so, by factors such as fire, urbanization, acid rain, electric lights (including "bug zappers"), overgrazing, agricultural expansion, pollution, deforestation, soil erosion, persistent adverse weather, off-road recreational vehicles, and logging, to name a few. The effect of pesticide drift (the potential effect of pesticide moving into non-target habitats) has an enormous effect on beetle population.

The presence of absence of beetles will stand as a measure of how we are doing in protecting the biosphere for present and future generations, for beetles play a significant part of a seasonal exchange between earth and sky, a pulse in the cycle of life.4

To date, only nine species of beetles have been listed under the United States Endangered Species Act, of which two are tiger beetles. The endangered Puritan Tiger Beetle Cicindela (Ellipsoptera) puritana occurs only along the Connecticut River in Vermont and New Hampshire and on the east and west sides of the Chesapeake Bay in Maryland. The threatened Northeastern Beach Tiger Beetle, Cicindela (Habroscelimorpha) dosalis dorsalis is now restricted to a single area in Massachussetts and a few sites in Maryland and Virginia.5

Types of Beetles

The following list of types of beetles is far from complete and is provided for reference purpose only:

  • Family Amphizoidae (trout-stream beetles)
  • Family Carabidae (ground beetles)
  • Family Cicindelidae (tiger beetles)
  • Family Dytiscidae (predaceous diving beetles)
  • Family Gyrinidae (whirligig beetles)
  • Family Haliplidae (crawling water beetles)
  • Family Noteridae (burrowing water beetles)
  • Family Rhysodidae (wrinkled bark beetles)
  • Family Cupedidae (reticulated beetles)
  • Family Micromalthidae (micromalthid beetles and telephone-pole beetles)
  • Family Hydroscaphidae (skiff beetles and water scavenger beetles)
  • Family Sphaeriidae (minute bog beetles)
  • Family Anobiidae (anobiid beetles)
  • Family Bostrichidae (branch and twig borers)
  • Family Lyctidae (powder-post beetles)
  • Family Ptinidae (spider beetles)
  • Family Buprestidae (metallic wood-boring beetle)
  • Family Byrrhidae (pill beetles)
  • Family Cantharidae (soldier beetles)
  • Family Lampyridae (fireflies and lightningbugs)
  • Family Lycidae (net-winged beetles)
  • Family Phengodidae (glow-worms)
  • Family Telegeusidae (telegeusid beetles)
  • Family Bruchidae (seed beetles)
  • Family Cerambycidae (long-horned beetles and sawyer beetles)
  • Family Chrysomelidae (leaf beetles)
  • Family Cleridae (checkered beetles)
  • Family Melyridae (solf-winged flower beetles)
  • Family Trogositidae (bark-gnawing beetles)
  • Family Byturidae (fruitworm beetles)
  • Family Cerylonidae (cerylonid beetles)
  • Family Ciidae (minute tree-fungus beetles)
  • Family Coccinellidae (lady beetles and ladybird beetles)
  • Family Corylophidae (minute fungus beetles)
  • Family Cryptophagidae (silken fungus beetles)
  • Family Cucujidae (flat bark beetles)
  • Family Discolomidae
  • Family Endomychidae (handsome fungus beetles)
  • Family Erotylidae (pleasing fungus beetles)
  • Family Languriidae (lizard beetles)
  • Family Lathridiidae (minute brown scavenger beetles)
  • Family Mycetophagidae (hairy fungus beetles)
  • Family Nitidulidae (sap beetles)
  • Family Phalacridae (shining flower beetles)
  • Family Rhizophagidae (root-eating beetles)
  • Family Sphindidae (dry-fungus beetles)
  • Family Aglycyderidae
  • Family Anthribidae (fungus weevils)
  • Family Apionidae
  • Family Brentidae (straight-snouted weevils)
  • Family Curculionidae (snout beetles and weevils)
  • Family Platypodidae (pin-hole borers)
  • Family Scolytidae (ambrosia beetles, bark beetles, engraver beetles, and timber beetles)
  • Family Clambidae (fringe-winged beetles)
  • Family Dascillidae (soft-bodied plant beetles)
  • Family Eucinetidae (plate-thigh beetles)
  • Family Geotrupidae
  • Family Helodidae (marsh beetles)
  • Family Rhipiceridae (cedar beetles)
  • Family Dermestidae (dermestid beetles and skin beetles)
  • Family Derodontidae (tooth-necked fungus beetles)
  • Family Jacobsoniidae
  • Family Nosodendridae (wounded-tree beetles)
  • Family Artematopidae (artematopid beetles)
  • Family Brachypsectridae (the texas beetle)
  • Family Callirhipidae (callirhipid beetles)
  • Family Chelonariidae (chelonarid beetles)
  • Family Dryopidae (long-toe water beetles)
  • Family Elmidae (riffle beetles)
  • Family Heteroceridae (variegated mud-loving beetles)
  • Family Limnichidae (minute marsh-loving beetles)
  • Family Psephenidae (water-penny beetles)
  • Family Ptilodactylidae (ptilodactylid beetles)
  • Family Cebrionidae (cebrionid beetles)
  • Family Cerophytidae (cerophytid beetles)
  • Family Elateridae (click beetles)
  • Family Eucnemidae (false click beetles)
  • Family Perothopidae (perothopid beetles)
  • Family Throscidae (throseid beetles)
  • Family Histeridae (hister beetles)
  • Family Sphaeritidae (false clown beetles)
  • Family Georyssidae (minute mud-loving beetles)
  • Family Hydraenidae (minute moss beetles)
  • Family Hydrophilidae (water scavenger beetles)
  • Family Lymexylonidae (ship-timber beetles)
  • Family Anthicidae (antlike flower beetles)
  • Family Euglenidae (antlike leaf beetles)
  • Family Meloidae (blister beetles)
  • Family Mordellidae (tumbling flower beetles)
  • Family Pedilidae (pedilid beetles)
  • Family Rhipiphoridae (wedge-shaped beetles)
  • Family Lucanidae (stag beetles)
  • Family Passalidae (bess beetles)
  • Family Scarabaeidae (scarab beetles)
  • Family Trogidae
  • Family Dasyceridae (dasycerid beetles)
  • Family Leiodidae (round fungus beetles)
  • Family Leptinidae (beaver parasites and mammal-nest beetles)
  • Family Limulodidae (horseshoe crab beetles)
  • Family Pselaphidae (short-winged mold beetles)
  • Family Ptiliidae (feather-winged beetles)
  • Family Scaphidiidae (shining fungus beetles)
  • Family Scydmaenidae (antlike stone beetles)
  • Family Silphidae (carrion beetles)
  • Family Staphylinidae (rove beetles)
  • Family Alleculidae (comb-clawed beetles)
  • Family Cephaloidae (false longhorn beetles)
  • Family Colydiidae (cylindrical bark beetles)
  • Family Inopeplidae (inopeplid beetles)
  • Family Lagriidae (long-jointed beetles)
  • Family Melandryidae (false darkling beetles)
  • Family Monommidae (monommid beetles)
  • Family Mycteridae (mycterid beetles)
  • Family Oedemeridae (false blister beetles)
  • Family Othniidae (false tiger beetles)
  • Family Pyrochroidae (fire-colored beetles)
  • Family Salpingidae (narrow-waisted bark beetles)
  • Family Tenebrionidae (darkling beetles)

References:
Reference file 7197-INS

 


 






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