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Order: Coleoptera
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Common Name--Beetles
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Names
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The order name Coleoptera is pronounced "co-le-OP-ter-a."
This name was first used by Aristotle in the fourth century B.C.
It is derived from the Greek words "koleos," which means sheath,
and "ptera," which means wings. The name refers to the fact
that most beetles have hardened front wings, termed elytra,
which cover the folded hind wings like a sheath.
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Insects in the order Coleoptera are commonly called beetles.
The common name "beetle" comes from older English words for a
"little biter". Some of the common names for groups
of species include tiger beetles, water beetles, ground
beetles, dung beetles, rove beetles, long-horned beetles,
chafers, weevils, and curculios. Larvae of some species are
called grubs, wireworms, and rootworms.
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Diversity
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We live in the "Age of Beetles." Coleoptera is the
largest order in the entire animal kingdom. There are more
species of beetles than species of plants. There are about
350,000 named species of beetles in the world and many more
unnamed species. In the United States and Canada, there are
almost 24,000 species, which is about 30% of all insect species
in the same area.
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The families of beetles containing the most species in North
America are the rove beetles (Staphylinidae, 3100 species),
the weevils (Curculionidae, 2432 species), the ground beetles
(Carabidae, 1700 species), the leaf beetles (Chrysomelidae,
1474 species), the scarab beetles (Scarabaeidae, 1375 species),
the darkling beetles (Tenebrionidae, 1300 species), and the
long-horned beetles (Cerambycidae, 1100 species).
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For an excellent article on the diversity of beetles, read
"Planet of the Beetles."
Chadwick, Dougls H. National Geographic,
Vol. 193 No. 3 (March 1998), 100-119.
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Habitats
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Beetles can be found in varied terrestrial and fresh-water
habitats. In addition to being associated with all kinds of
plants, they can be found in logs or under bark, in fungi, in
mud, in decaying plant and animal matter, in water, in stored
food, in bird and mammal nests, and in termite nests. Species
in the genus Cremastocheilas (family Scarabaeidae) live
in ant nests and feed on ant larvae. Many beetles live deep in
the soil or in decaying leaf litter on the ground. Other beetles
live under rocks or in caves.
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Mammal nest beetles (family Leptinidae) are external parasites
of mammals, including beavers. These beetles live in the fur
or the nests of their hosts. Some scarab beetles in the genus
Trox live in bird and mammal nests apparently feeding
on the droppings of the animals or the remains of their food.
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Form and Function
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Adult beetles range in size from 0.01 to almost 8 inches in
body length, but antennae of some are much longer than their
bodies. Beetles usually have hard bodies, but sometimes they
are leathery or even soft bodied. These bodies may be very smooth
or very hairy. The majority of beetles are dark brown or black,
but many are red, blue, green, purple or a combination of
colors.
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Beetles have many types of antennae. These may include forms
that are threadlike, sawtoothed, comblike, feather-like, or
clubbed. Some beetles have "lamellate" antennae with
segments at the end of the antennae that have long, plate-like
projections on one side. Weevils have "elbowed"
antennae, with an elbow-shaped joint between the long first
segment and remaining shorter segments.
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Beetle mouthparts are usually the biting and chewing type with
well-developed mandibles being present. The mandibles may be
very large and resemble the antlers of deer in males of stag
beetles. Mandibles of some beetles are used in defense or
mating rather than in eating. Mandibles of some predaceous
larvae are grooved or have a tube inside for injecting
digestive enzymes into the prey.
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Beetles usually have two sets of wings, the hard front wings,
or elytra (elytron is singular), and the membranous hind wings.
The hind wings are folded under the elytra when not in use.
The elytra usually extend to the tip, or near the tip, of the
abdomen. A distinctive feature of Coleoptera is that the elytra
meet in a straight line on the back. Some beetles, such as
rove beetles, have short elytra, and most of the abdomen is
exposed.
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The three pairs of legs in beetle species may be modified for
swimming, digging, running, grasping, or other activities.
Flea beetles (family Chrysomelidae) have hind legs modified for
jumping. Males of some water beetles have wide tarsal
segments for holding the female during mating. Many scarab
beetles have sharp spines on their legs that are used for
defense against vertebrate predators.
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Beetle larvae can be of different shapes and sizes. Some are
wormlike and legless, and others are more like caterpillars,
with thoracic legs and abdominal prolegs. Wireworms, such as
larvae of click beetles, have short legs and are long, hard,
and wirelike. Many larvae have C-shaped bodies and are
usually soft. This form of larva, which is present in scarabs
and other beetles, often is called a grub. Many predaceous
larvae have long legs for running along the ground.
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Pupae are like pale, mummified versions of the adult beetle.
The legs and wings project from the pupa, rather than being
fused with the body as in Lepidoptera. In some species the
pupa is surrounded by a silk cocoon or a round chamber made of
hardened earth.
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Life Cycle
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Beetles have complete metamorphosis with egg, larva, pupa, and
adult. Females of some beetles keep the eggs inside their
bodies and give birth to live larvae. Blister beetles (family
Meloidae) have a unique type of metamorphosis, termed
hypermetamorphosis, in which the larva changes into different
forms of larvae during its development. A blister beetle egg
hatches into an active, long-legged larva. As the larva molts and
becomes larger, it changes into a C-shaped larva with shorter
legs. This form of larva molts into a legless instar that
does not feed. Eventually, the legless instar molts into the
pupa with legs and wings projecting from its body.
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In some beetles, the adults help take care of the young larvae,
which is a simple form of social behavior. Females of rove
beetles in the genus Bledius (family Staphylinidae)
build, maintain, and defend larval tunnels and also provide
algae for the larvae to eat. Males and females of some
Scarabaeidae cooperate in digging nests and providing their
larvae with food. Bess beetles (family Passalidae) and species
in other families of insects also care for their young.
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Most beetle larvae pass through 3-5 instars. Some beetles may
have as many as 30 instars, while one species of cave beetle is
known to have only one instar. At the end of the final larval
instar, the larva molts into the pupal stage. After the pupal
stage, the adult beetle will emerge to feed, mate, and produce
eggs for another generation. A few weevils, leaf beetles, and
other beetles can reproduce without mating (parthenogenesis).
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Most beetles have one generation per year, although some may
have two or more in warm regions. Many scarab beetles require
two to three years to complete one generation. Some
long-horned beetles (family Cerambycidae) have been known to
take thirty years to complete their life cycle.
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Form and Feeding Habits
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Most beetles are either plant feeding or predaceous. Some
species have different feeding habits in different stages, such
as those with predaceous larvae and plant-feeding adults. Many
species feed as scavengers on dead plants and animals. Other
species feed on fungi or mold, and a few are parasitic on other
insects or vertebrate animals.
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Among the insects, beetles are the most important group of
ground-dwelling predators. Beetles will prey on both active
and inactive stages, such as eggs and pupae, of a wide range
of insects and other prey. However, adults of some ground
beetles (family Carabidae) and many lightning beetles (family
Lampyridae) prey mainly on snails. Many beetles that live
in decaying leaves on the ground, or leaf litter, prey on mites
(class Arachnida). Some predators can be omnivorous, with the
larva or adult feeding on both plants and animals. Soldier
beetles (family Cantharidae) and others have predaceous larvae
and plant-feeding adults.
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A unique form of predation among the Coleoptera is present with
larvae of tiger beetles. Most beetles are active
hunters of prey, but tiger beetle larvae, also known as "chicken
chokers," wait in burrows in the ground. These larvae have a
large bump on their backs that help them hold their bodies in
the burrow. When an insect walks over their camouflaged heads,
they grab the prey with long mandibles.
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Most kinds of plants are eaten by some kind of beetle. Many
beetles have specific parts of the plant that they eat. Adults
and larvae of many beetles chew off parts of leaves. Larvae of
some beetles are leaf miners, eating trails inside the leaves.
Other beetles bore in stems or fruit. Some kinds of beetle
larvae, including white grubs and rootworms, feed on roots.
Many adult beetles can be found in flowers where they may feed
on the petals, nectar, or pollen. Some beetles feed on sap
that flows from a tree wound.
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Larvae of long-horned beetles (family Cerambycidae) and
metallic wood-boring beetles (family Buprestidae) bore in the
wood of shrubs and trees, especially those that are dying or
dead. The female twig-girdler, a kind of long-horned beetle,
lays an egg at the end of a branch on a living tree. Then, the
female chews, or girdles, the stem to cut off the water supply.
The tip of the branch dies and usually falls to the ground.
The larva of the twig-girdler then feeds inside the dead
branch. Metallic wood-borers are known also as jewel beetles.
More information on these beetles with images of some living
jewels can be found at
The Buprestid Gallery.
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Bark beetles (family Scolytidae) feed under the bark of trees.
Some bark beetles are known as engraver beetles because their
feeding galleries make distinctive patterns on the wood. Other
bark beetles are called ambrosia beetles because they feed on
a kind of fungus, known as ambrosia, that they grow in their
tunnels.
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Beetles in several families of Coleoptera eat various kinds of
fungi. Some eat bracket fungi that grow on trees, and others
prefer mushrooms or puffballs on the ground. Some beetles in
fungi are actually predators that are eating larvae of beetles,
flies, and other insects eating the fungi. Many beetles can
be found in leaf litter that has fungi and bacteria aiding
decay of the leaves. Sometimes it is not known if the beetle
is eating fungi or is eating the decaying leaves and other
organic materials.
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Several groups of beetles feed on animal droppings, or dung.
Some dung beetles (family Scarabaeidae) feed on the dung where
it falls on the ground, sometimes burrowing into the ground
under the dung pile. Tumblebugs are dung beetles that form a
round ball of dung and roll it away to another location where
it won't be disturbed by other insects that eat the same food.
Different species of dung beetles prefer different kinds of
animal droppings. Some cave beetles feed on bat droppings.
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Certain species in the families Scarabaeidae, Dermestidae, and
Silphidae feed on decaying animal flesh, or carrion. Some
carrion beetles (Silphidae) bury small animals several inches
below the surface of the soil. After finding a suitable spot
for burial, a mating pair of these beetles work together to
move the carcass and bury it. The beetles will feed on the
buried carrion and lay eggs on it as well. The developing
larvae may feed on the carrion for three or four weeks.
Information on an endangered species of carrion beetle can be
found at
The American Burying Beetle.
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Coleoptera includes several species that feed on stored food,
furniture, and wood in houses. Mealworms, flour beetles, and
grain beetles can be found in kitchen pantries where they feed
on a wide variety of dried plant and animal products. Some
species in the families Anobiidae and Lyctidae are known as
powderpost beetles. These beetles bore into dry wood,
including wood and furniture in houses. The beetles make piles
of powdery dust, composed of sawdust and their droppings,
outside the entrances of their burrows.
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Natural Enemies
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Both adults and larvae of aquatic beetles are eaten by fish,
frogs, birds, and turtles. Terrestrial beetles also provide
food for many vertebrate animals, especially small mammals like
shrews and mice. Toads eat many ground beetles (family
Carabidae). Wood-boring beetles are a major part of the diet of
woodpeckers.
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Beetle eggs and larvae may be parasitized by wasps in the
families Mymaridae, Ichneumonidae, Chalcididae, Braconidae, and
other families. Flies in the family Tachinidae parasitize
beetle larvae, and flies in Pyrgotidae parasitize adult scarab
beetles. Beetles also may be preyed upon by spiders, certain
wasps in the family Tiphiidae, and other beetles.
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Olympic Feats and Other Strange Facts
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Adults and larvae lightning beetles (Lampyridae) are not the
only ones that produce light. Adults of some click beetles
have light-producing spots on their thoraxes. Larvae of
Phengodidae also produce light and are known as glowworms.
Adults of glowworms are strange-appearing beetles because of
their feathery antennae and short elytra.
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Adults of the lead cable borer, Scobicia declivis
(family Bostrichidae), often bore through the lead covering
telephone lines. Although the beetles do not appear to feed
on the lead, they do create holes that allow moisture to enter
the cables. This can cause the wires to short circuit and
interrupt phone service.
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The heads of some weevils are longer than the rest of their
bodies. Weevils have the front part of their heads stretched
out to form long snouts. The weevil can feed inside nuts and
fruits with their mandibles at the end of these snouts.
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The smallest beetle in the world is the feather-winged beetle
Nanosella fungi in the family Ptiliidae which measures
about one-hundredth of an inch in length.
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The heaviest beetle in the world is the African goliath beetle,
which may weigh 3.5 ounces or more. In addition, these beetles
measure up to five inches in length. The goliath beetle weighs
approximately 40 million times as much as the smallest beetle
in the world.
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The longest beetles in the world are the long-horned beetles
(Cerambycidae) Titanus giganteus from South America and
Xixuthrus heros from Fiji. Both of these beetles may
attain a length of almost 8 inches.
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The aquatic whirligig beetles (Gyrinidae), which swim along
the surface of water, have divided compound eyes. The upper eye
on each side of the head sees above the water, and the lower
eye sees below the surface of the water.
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Adult predaceous diving beetles, in the family Dytiscidae, can
stay under water for thirty-six hours even though they do not
have gills or other structures for breathing under water. They
obtain air from the water surface and carry the air under their
elytra.
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When adult click beetles (Elateridae) are placed on their backs,
they have the ability to flip themselves over, sometimes going
several inches into the air. This is done when the beetle
arches its body, then suddenly snaps a pointed projection on
the bottom of its prothorax into a small groove on the
mesothorax. The eyed click beetle has two spots on its
pronotum that resemble eyes, which may frighten predators,
especially when the beetle flips into the air.
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In ancient Egypt, the dung beetle, Scarabaeus sacer,
was very important in mythology. The dung-ball-rolling
behavior of this beetle was said to symbolize the movement of
the sun across the sky and the Egyptian sun god, Ra. It also
was believed that the scarab had supernatural powers which
would insure rebirth after death. In some cases, green carved
scarabs were used to replace the hearts in mummies.
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Blister beetles (family Meloidae) emit "blood" from
certain parts of their bodies when disturbed. This liquid can
cause large, watery blisters to appear on the skin of animals
coming in contact with one of these beetles.
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An African leaf beetle, Diamphidia simplex (Chrysomelidae),
exudes a poison that causes death by paralysis. African
bushmen use this poison on their arrow tips to kill animals.
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Bombardier beetles in the genus Brachinus (Carabidae)
emit an offensive gas as a means of self-defense. The gas is
boiling hot when it is sprayed out with a popping sound.
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The Good and The Bad
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Major crop pests include species in the families Chrysomelidae
(cucumber beetles, flea beetles, Colorado potato beetle),
Curculionidae (weevils), and Scarabaeidae (white grubs,
Japanese beetle). Adults of cucumber beetles can transmit
plant diseases, and their larvae, known as rootworms, are
pests of corn and other crops. Weevil pests include the cotton
boll weevil, plum curculio, and many others. White grubs
feed on roots of grasses, and they are pests in pastures, crops,
golf courses, and lawns. The Japanese beetle has a white
grub that is a grass pest and an adult that is a pest of
fruits and shrubs. Photographs of many beetle pests can be
found at
The University of Nebraska Image Gallery.
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Many beetles are pests of the forestry industry, either of the
living tree or of wood products. Bark beetles are perhaps
the most serious group of pests, especially of pine trees.
Some bark beetles transmit fungi or viruses that can kill the
tree. Wood may be damaged by long-horned beetles, metallic
wood borers, branch borers (Bostrichidae), and other beetles.
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Some beetles attack plant or animal products in homes and
various places of storage. Granary weevils and rice weevils
are major pests of stored grain. Other beetles feed on flour,
cheeses, meats, cereals, and other products stored in the
kitchen pantry. Carpet beetles (Dermestidae) are a major
pest of plant and animal products in the home, including rugs,
curtains, silk, fur, and leather.
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Many beetles are quite beneficial. Dung beetles remove animal
droppings, reduce numbers of flies, and help the soil. Carrion
beetles feed on dead and decaying plants or animals and help
in the decomposition cycle. Ladybird beetles and other
predators prey on aphids, scale insects, and other pests that
damage crops. Photographs and descriptions of common ladybird
beetles can be found at
Biological Control. Many beetles and larvae are
an important source of food for other animals. Although flour
beetles in the genus Tribolium (Tenebrionidae) are pests,
they also are used for research on genetics.
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Beetles have long held an important place in the world of art,
literature, and mythology. Scarab beetles were regarded highly
in ancient Egypt and were frequently the models for carvings,
paintings, and jewelry. The brightly colored elytra of
metallic wood-boring beetles, such as the South American
Euchroma gigantea, have been used to make jewelry and
other works of art.
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Taxonomy
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Selected Families of North American Coleoptera
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Anobiidae (death-watch beetles)
Anthicidae (antlike flower beetles)
Bostrichidae (branch-and-twig borers)
Bruchidae (seed beetles)
Buprestidae (metallic wood-boring beetles)
Cantharidae (soldier beetles)
Carabidae (ground beetles)
Cerambycidae (long-horned beetles)
Chrysomelidae (leaf beetles)
Cicindelidae (tiger beetles)
Cleridae (checkered beetles)
Coccinellidae (lady or ladybird beetles)
Cucujidae (flat bark beetles)
Curculionidae (snout beetles)
Dermestidae (dermestid beetles)
Dytiscidae (predaceous diving beetles)
Elateridae (click beetles)
Elmidae (riffle beetles)
Erotylidae (pleasing fungus beetles)
Gyrinidae (whirligig beetles)
Haliplidae (crawling water beetles)
Histeridae (hister beetles)
Hydrophilidae (water scavenger beetles)
Lampyridae (lightningbugs or fireflies)
Leiodidae (round fungus beetles)
Leptinidae (mamal-nest beetles)
Lucanidae (stag beetles)
Lycidae (net-winged beetles)
Lyctidae (powder-post beetles)
Melandryidae (false darkling beetles)
Meloidae (blister beetles)
Melyridae (soft-winged flower beetles)
Mordellidae (tumbling flower beetles)
Nitidulidae (sap beetles)
Passalidae (passalid beetles)
Pedilidae (pedilid beetles)
Phalacridae (shining mold beetles)
Phengodidae (glowworms)
Pselaphidae (short-winged mold beetles)
Psephenidae (water-penny beetles)
Ptiliidae (feather-winged beetles)
Scarabaeidae (scarab beetles)
Scolytidae (bark-and-ambrosia beetles)
Silphidae (carion beetles)
Staphylinidae (rove beetles)
Tenebrionidae (darkling beetles)
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Selected References
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Arnett, R. H. Jr. American Insects, A Handbook of the
Insects of America North of Mexico. New York: Van
Nostrand Reinhold Co., 1985.
Borror, D. J., Triplehorn, C. A., and Johnson, N. F. An
Introduction to the Study of Insects. Sauders College
Publishing, 1989.
Dillon, E. S., and Dillon, L. S. A Manual of the Common
Beetles of Eastern North America, Volumes One and Two.
New York: Dover Publications, Inc., 1961.
Hutchins, R. E. Insects in Armor - A Beetle Book. New
York: Parents Magazine Press, 1972.
Jacques, H. E. How to Know the Beetles. Dubuque, Iowa:
William.C. Brown Co., 1951.
White, R. E. A Field Guide to the Beetles of North America.
Boston: Houghton Mifflin Co, 1983.
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Links
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For an extensive list of Coleoptera Web sites, go to the Links Component of the module.
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Picture Credits
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Smithsonian Institution
Side View, Whirligig Beetle Eyes
Dr. Ross E. Hutchins (Deceased)
Mississippi Entomological Museum
Hercules beetle with spotted elytra
Stag beetle males fighting with mandibles
Colorado potato beetle with elytra meeting in straight line
White grub of scarab beetle
Pupa of lightning beetle
Larva of lightning beetle
Larva of tiger beetle
Twig girdler
Galleries of Scolytus engraver beetles
A bracket fungus - food for many beetles
Adult glowworm beetle
Acorn weevil with long snout
The eyed click beetle
Cotton boll weevil
Joe MacGown
Mississippi Entomological Museum
Cremastocheilas harrisii, a predator of ant larvae
Polyphylla scarab beetle with lamellate antennae
Phaneus dung beetle
Richard L. Brown
Mississippi Entomological Museum
Euchroma gigantea with elytra used for jewelry
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