Beetle

Order of insects

For other uses, see Beetle (disambiguation).

"Beetles" redirects here. For the English rock band, see The Beatles.

"Coleoptera" redirects here. Not to be confused with Coeloptera or Cleopatra.

Beetle Temporal range: 299–0  Ma PreꞒ Ꞓ O S D C P T J K Pg N Earliest Permian–Present
Clockwise from top left: female golden stag beetle ( Rhinotia hemistictus), cowboy beetle (Chondropyga dorsalis), and a species of Amblytelus
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
(unranked):	Endopterygota
Order:	Coleoptera Linnaeus, 1758
Suborders[1]
Adephaga Archostemata Myxophaga Polyphaga †Protocoleoptera See subgroups of the order Coleoptera

Beetles are

polar regions, they interact with their ecosystems in several ways: beetles often feed on plants and fungi, break down animal and plant debris, and eat other invertebrates. Some species are serious agricultural pests, such as the Colorado potato beetle, while others such as Coccinellidae (ladybirds or ladybugs) eat aphids, scale insects, thrips

, and other plant-sucking insects that damage crops.

Beetles typically have a particularly hard

metamorphosis, with a series of conspicuous and relatively abrupt changes in body structure between hatching and becoming adult after a relatively immobile pupal stage. Some, such as stag beetles, have a marked sexual dimorphism, the males possessing enormously enlarged mandibles which they use to fight other males. Many beetles are aposematic, with bright colors and patterns warning of their toxicity, while others are harmless Batesian mimics of such insects. Many beetles, including those that live in sandy places, have effective camouflage

.

Beetles are prominent

lady beetles and dung beetles

are beneficial by helping to control insect pests.

Etymology

Staatliches Museum für Naturkunde Karlsruhe

, Germany

The name of the taxonomic order, Coleoptera, comes from the Greek koleopteros (κολεόπτερος), given to the group by Aristotle for their elytra, hardened shield-like forewings, from koleos, sheath, and pteron, wing. The English name beetle comes from the Old English word bitela, little biter, related to bītan (to bite),^[2][3] leading to Middle English betylle.^[4] Another Old English name for beetle is ċeafor, chafer, used in names such as cockchafer, from the Proto-Germanic *kebrô ("beetle"; compare German Käfer, Dutch kever).^[5]

Distribution and diversity

Beetles are by far the largest order of insects: the roughly 400,000 species make up about 40% of all insect species so far described, and about 25% of all animal species.^{[1][6][7][8][9][10]} A 2015 study provided four independent estimates of the total number of beetle species, giving a mean estimate of some 1.5 million with a "surprisingly narrow range"^[11] spanning all four estimates from a minimum of 0.9 to a maximum of 2.1 million beetle species. The four estimates made use of host-specificity relationships (1.5 to 1.9 million), ratios with other taxa (0.9 to 1.2 million), plant:beetle ratios (1.2 to 1.3), and extrapolations based on body size by year of description (1.7 to 2.1 million).^[11][12]

This immense diversity led the evolutionary biologist

Beetles are found in nearly all habitats, including freshwater and coastal habitats, wherever vegetative foliage is found, from trees and their bark to flowers, leaves, and underground near roots - even inside plants in galls, in every plant tissue, including dead or decaying ones.[14] Tropical forest canopies have a large and diverse fauna of beetles,^[15] including Carabidae,^[16] Chrysomelidae,^[17] and Scarabaeidae.^[18]

The heaviest beetle, indeed the heaviest insect stage, is the

• 

  Titan beetle, Titanus giganteus, a tropical longhorn, is one of the largest and heaviest insects in the world.

• 

  Scydosella musawasensis

  , the smallest known beetle: scale bar (right) is 50 μm.

• 

  Hercules beetle, Dynastes hercules ecuatorianus, the longest of all beetles

• 

  iridescent Protaetia cuprea feeding on thistle

Evolution

Late Paleozoic and Triassic

Fossil and life restoration of Moravocoleus permianus (Tshekardocoleidae

) from the Early Permian of the Czech Republic, representative of the morphology of early beetles

Curculionoidea) and click beetles (e.g. Elateroidea) appeared. The first jewel beetles (e.g. Buprestidae) are present, but they remained rare until the Cretaceous.^[30][31][32] The first scarab beetles were not coprophagous but presumably fed on rotting wood with the help of fungus; they are an early example of a mutualistic

relationship.

There are more than 150 important fossil sites from the Jurassic, the majority in Eastern Europe and North Asia. Outstanding sites include Solnhofen in Upper Bavaria, Germany,^[33] Karatau in South Kazakhstan,^[34] the Yixian formation in Liaoning, North China,^[35] as well as the Jiulongshan formation and further fossil sites in Mongolia. In North America there are only a few sites with fossil records of insects from the Jurassic, namely the shell limestone deposits in the Hartford basin, the Deerfield basin and the Newark basin.^[25][36]

Cretaceous

The

Cerambycidae) were rather rare: their diversity increased only towards the end of the Upper Cretaceous.^[25] The first coprophagous beetles are from the Upper Cretaceous^[38] and may have lived on the excrement of herbivorous dinosaurs.^[39] The first species where both larvae and adults are adapted to an aquatic lifestyle are found. Whirligig beetles (Gyrinidae) were moderately diverse, although other early beetles (e.g. Dytiscidae) were less, with the most widespread being the species of Coptoclavidae, which preyed on aquatic fly larvae.^[25]

A 2020 review of the palaeoecological interpretations of fossil beetles from Cretaceous ambers has suggested that

fungivorous species in particular appearing to dominate.^[40]

Many fossil sites worldwide contain beetles from the Cretaceous. Most are in Europe and Asia and belong to the temperate climate zone during the Cretaceous.

Las Hoyas. In Australia, the Koonwarra fossil beds of the Korumburra group, South Gippsland, Victoria, are noteworthy. Major sites from the Upper Cretaceous include Kzyl-Dzhar in South Kazakhstan and Arkagala in Russia.^[25]

Cenozoic

structural color^[41]

Beetle fossils are abundant in the Cenozoic; by the Quaternary (up to 1.6 mya), fossil species are identical to living ones, while from the Late Miocene (5.7 mya) the fossils are still so close to modern forms that they are most likely the ancestors of living species. The large oscillations in climate during the Quaternary caused beetles to change their geographic distributions so much that current location gives little clue to the biogeographical history of a species. It is evident that geographic isolation of populations must often have been broken as insects moved under the influence of changing climate, causing mixing of gene pools, rapid evolution, and extinctions, especially in middle latitudes.^[42]

Phylogeny

The very large number of beetle species poses special problems for classification. Some families contain tens of thousands of species, and need to be divided into subfamilies and tribes. Polyphaga is the largest suborder, containing more than 300,000 described species in more than 170 families, including rove beetles (Staphylinidae), scarab beetles (Scarabaeidae), blister beetles (Meloidae), stag beetles (Lucanidae) and true weevils (Curculionidae).^[9][43] These polyphagan beetle groups can be identified by the presence of cervical sclerites (hardened parts of the head used as points of attachment for muscles) absent in the other suborders.^[44]

testes are tubular and the first abdominal sternum (a plate of the exoskeleton) is divided by the hind coxae (the basal joints of the beetle's legs).^[45]

reticulated beetles (Cupedidae) and the telephone-pole beetle.^[46]

The Archostemata have an exposed plate called the metatrochantin in front of the basal segment or coxa of the hind leg.[47] Myxophaga contains about 65 described species in four families, mostly very small, including Hydroscaphidae and the genus Sphaerius.^[48] The myxophagan beetles are small and mostly alga-feeders. Their mouthparts are characteristic in lacking galeae and having a mobile tooth on their left mandible.^[49]

The consistency of beetle

Early Permian.^{[52][54][55][56]}

Molecular phylogenetic analysis confirms that the Coleoptera are monophyletic. Duane McKenna et al. (2015) used eight nuclear genes for 367 species from 172 of 183 Coleopteran families. They split the Adephaga into 2 clades, Hydradephaga and Geadephaga, broke up the Cucujoidea into 3 clades, and placed the Lymexyloidea within the Tenebrionoidea. The Polyphaga appear to date from the Triassic. Most extant beetle families appear to have arisen in the Cretaceous.[56] The cladogram is based on McKenna (2015).^[56] The number of species in each group (mainly superfamilies) is shown in parentheses, and boldface if over 10,000.^[57] English common names are given where possible. Dates of origin of major groups are shown in italics in millions of years ago (mya).^[57]

Coleoptera	240 mya Adephaga Carabidae (ground beetles) 200 mya Polyphaga Derodontoidea (29) 200 mya Staphylinidae 195 mya (48,000, rove beetles) Elateriformia Nosodendridae (70) 190 mya 190 mya Cucujiformia Lymexyloidea Phytophaga Chrysomeloidea Chrysomelidae (35,000, leaf beetles) Cerambycidae (25,000, longhorn beetles) Curculionoidea (97,000, weevils) 170 mya 225 mya
285 mya

External morphology

Beetle body structure, using cockchafer

. A: head, B: thorax, C: abdomen. 1: antenna, 2: compound eye, 3: femur, 4: elytron (wing cover), 5: tibia, 6: tarsus, 7: claws, 8: mouthparts, 9: prothorax, 10: mesothorax, 11: metathorax, 12: abdominal sternites, 13: pygidium.

Beetles are generally characterized by a particularly hard exoskeleton and hard forewings (elytra) not usable for flying. Almost all beetles have mandibles that move in a horizontal plane. The mouthparts are rarely suctorial, though they are sometimes reduced; the maxillae always bear palps. The antennae usually have 11 or fewer segments, except in some groups like the Cerambycidae (longhorn beetles) and the Rhipiceridae (cicada parasite beetles). The coxae of the legs are usually located recessed within a coxal cavity. The genitalic structures are telescoped into the last abdominal segment in all extant beetles. Beetle larvae can often be confused with those of other endopterygote groups.^[47] The beetle's exoskeleton is made up of numerous plates, called sclerites, separated by thin sutures. This design provides armored defenses while maintaining flexibility. The general anatomy of a beetle is quite uniform, although specific organs and appendages vary greatly in appearance and function between the many families in the order. Like all insects, beetles' bodies are divided into three sections: the head, the thorax, and the abdomen.^[7] Because there are so many species, identification is quite difficult, and relies on attributes including the shape of the antennae, the tarsal formulae^[a] and shapes of these small segments on the legs, the mouthparts, and the ventral plates (sterna, pleura, coxae). In many species accurate identification can only be made by examination of the unique male genitalic structures.^[58]

Head

Lamia textor

The head, having mouthparts projecting forward or sometimes downturned, is usually heavily

Polyphylla fullo has distinctive fan-like antennae

, one of several distinct forms for the appendages among beetles.

Beetle antennae are primarily organs of sensory perception and can detect motion, odor and chemical substances,^[62] but may also be used to physically feel a beetle's environment. Beetle families may use antennae in different ways. For example, when moving quickly, tiger beetles may not be able to see very well and instead hold their antennae rigidly in front of them in order to avoid obstacles.^[63] Certain Cerambycidae use antennae to balance, and blister beetles may use them for grasping. Some aquatic beetle species may use antennae for gathering air and passing it under the body whilst submerged. Equally, some families use antennae during mating, and a few species use them for defense. In the cerambycid Onychocerus albitarsis, the antennae have venom injecting structures used in defense, which is unique among arthropods.^[64] Antennae vary greatly in form, sometimes between the sexes, but are often similar within any given family. Antennae may be clubbed, threadlike, angled, shaped like a string of beads, comb-like (either on one side or both, bipectinate), or toothed. The physical variation of antennae is important for the identification of many beetle groups. The Curculionidae have elbowed or geniculate antennae. Feather like flabellate antennae are a restricted form found in the Rhipiceridae and a few other families. The Silphidae have a capitate antennae with a spherical head at the tip. The Scarabaeidae typically have lamellate antennae with the terminal segments extended into long flat structures stacked together. The Carabidae typically have thread-like antennae. The antennae arises between the eye and the mandibles and in the Tenebrionidae, the antennae rise in front of a notch that breaks the usually circular outline of the compound eye. They are segmented and usually consist of 11 parts, the first part is called the scape and the second part is the pedicel. The other segments are jointly called the flagellum.^[62][65][66]

Beetles have

Acilius sulcatus, a diving beetle with hind legs adapted as swimming

limbs

Checkered beetle Trichodes alvearius

taking off, showing the hard elytra (forewings adapted as wing-cases) held stiffly away from the flight wings

The abdomen is the section behind the metathorax, made up of a series of rings, each with a hole for breathing and respiration, called a spiracle, composing three different segmented sclerites: the tergum, pleura, and the sternum. The tergum in almost all species is membranous, or usually soft and concealed by the wings and elytra when not in flight. The pleura are usually small or hidden in some species, with each pleuron having a single spiracle. The sternum is the most widely visible part of the abdomen, being a more or less sclerotized segment. The abdomen itself does not have any appendages, but some (for example, Mordellidae) have articulating sternal lobes.^[74]

Anatomy and physiology

A beetle's body systems

The nervous system in beetles contains all the types found in insects, varying between different species, from three thoracic and seven or eight abdominal ganglia which can be distinguished to that in which all the thoracic and abdominal ganglia are fused to form a composite structure.^[7]

Respiratory system

Dytiscus spiracles

(right) on upper side of abdomen, normally covered by the elytra, are in contact with an air bubble when the beetle dives.

Diving beetles, such as the Dytiscidae, carry a bubble of air with them when they dive. Such a bubble may be contained under the elytra or against the body by specialized hydrophobic hairs. The bubble covers at least some of the spiracles, permitting air to enter the tracheae.^[7] The function of the bubble is not only to contain a store of air but to act as a physical gill. The air that it traps is in contact with oxygenated water, so as the animal's consumption depletes the oxygen in the bubble, more oxygen can diffuse in to replenish it.^[75] Carbon dioxide is more soluble in water than either oxygen or nitrogen, so it readily diffuses out faster than in. Nitrogen is the most plentiful gas in the bubble, and the least soluble, so it constitutes a relatively static component of the bubble and acts as a stable medium for respiratory gases to accumulate in and pass through. Occasional visits to the surface are sufficient for the beetle to re-establish the constitution of the bubble.^[76]

Circulatory system

Like other insects, beetles have

Tympanal organs or hearing organs consist of a membrane (tympanum) stretched across a frame backed by an air sac and associated sensory neurons, are found in two families.^[78] Several species of the genus Cicindela (Carabidae) have hearing organs on the dorsal surfaces of their first abdominal segments beneath the wings; two tribes in the Dynastinae (within the Scarabaeidae) have hearing organs just beneath their pronotal shields or neck membranes. Both families are sensitive to ultrasonic frequencies, with strong evidence indicating they function to detect the presence of bats by their ultrasonic echolocation.^[7]

Reproduction and development

Beetles are members of the

Punctate flower chafers

(Neorrhina punctata, Scarabaeidae) mating

Some beetles have intricate mating behaviour. Pheromone communication is often important in locating a mate. Different species use different pheromones. Scarab beetles such as the Rutelinae use pheromones derived from fatty acid synthesis, while other scarabs such as the Melolonthinae use amino acids and terpenoids. Another way beetles find mates is seen in the fireflies (Lampyridae) which are bioluminescent, with abdominal light-producing organs. The males and females engage in a complex dialog before mating; each species has a unique combination of flight patterns, duration, composition, and intensity of the light produced.^[7]

Before mating, males and females may stridulate, or vibrate the objects they are on. In the Meloidae, the male climbs onto the dorsum of the female and strokes his antennae on her head, palps, and antennae. In

fertilize the egg.^[6]

Life cycle

The life cycle of the stag beetle includes three instars

.

Egg

Essentially all beetles lay eggs, though some

ovoviviparous, laying eggs which hatch almost immediately. Beetle eggs generally have smooth surfaces and are soft, though the Cupedidae

have hard eggs. Eggs vary widely between species: the eggs tend to be small in species with many instars (larval stages), and in those that lay large numbers of eggs. A female may lay from several dozen to several thousand eggs during her lifetime, depending on the extent of parental care. This ranges from the simple laying of eggs under a leaf, to the parental care provided by scarab beetles, which house, feed and protect their young. The Attelabidae roll leaves and lay their eggs inside the roll for protection.^[7][81]

Larva

The

skin beetles undergo a degree of reversed development when starved, and later grow back to the previously attained level of maturity. The cycle can be repeated many times (see Biological immortality).^[82] Larval morphology is highly varied amongst species, with well-developed and sclerotized heads, distinguishable thoracic and abdominal segments (usually the tenth, though sometimes the eighth or ninth).^[6]

Scarabaeiform larva of Hercules beetle

Beetle larvae can be differentiated from other insect larvae by their hardened, often darkened heads, the presence of chewing mouthparts, and spiracles along the sides of their bodies. Like adult beetles, the larvae are varied in appearance, particularly between beetle families. Beetles with somewhat flattened, highly mobile larvae include the ground beetles and rove beetles; their larvae are described as campodeiform. Some beetle larvae resemble hardened worms with dark head capsules and minute legs. These are elateriform larvae, and are found in the click beetle (Elateridae) and darkling beetle (Tenebrionidae) families. Some elateriform larvae of click beetles are known as wireworms. Beetles in the Scarabaeoidea have short, thick larvae described as scarabaeiform, more commonly known as grubs.^[83]

All beetle larvae go through several

carabid beetle. In another week it moults and assumes the appearance of a scarabaeid larva—the scarabaeidoid stage. Its penultimate larval stage is the pseudo-pupa or the coarcate larva, which will overwinter and pupate until the next spring.^[85]

The larval period can vary widely. A fungus feeding staphylinid Phanerota fasciata undergoes three moults in 3.2 days at room temperature while Anisotoma sp. (Leiodidae) completes its larval stage in the fruiting body of slime mold in 2 days and possibly represents the fastest growing beetles. Dermestid beetles, Trogoderma inclusum can remain in an extended larval state under unfavourable conditions, even reducing their size between moults. A larva is reported to have survived for 3.5 years in an enclosed container.^[7]

Pupa and adult

The ivory-marked beetle, Eburia quadrigeminata, may live up to 40 years inside the hardwoods

on which the larva feeds.

As with all endopterygotes, beetle larvae pupate, and from these

exarate; in a few beetles (Staphylinidae, Ptiliidae etc.) the appendages are fused with the body (termed as obtect pupae).^[6]

Adults have extremely variable lifespans, from weeks to years, depending on the species.

Cerambycidae), while Buprestis aurulenta and other Buprestidae have been documented as emerging as much as 51 years after manufacture of wooden items.^[86]

Behaviour

Locomotion

Photinus pyralis

, firefly, in flight

The elytra allow beetles to both fly and move through confined spaces, doing so by folding the delicate wings under the elytra while not flying, and folding their wings out just before takeoff. The unfolding and folding of the wings is operated by muscles attached to the wing base; as long as the tension on the radial and cubital veins remains, the wings remain straight.[7] Some beetle species (many Cetoniinae; some Scarabaeinae, Curculionidae and Buprestidae) fly with the elytra closed, with the metathoracic wings extended under the lateral elytra margins.^[87] The altitude reached by beetles in flight varies. One study investigating the flight altitude of the ladybird species Coccinella septempunctata and Harmonia axyridis using radar showed that, whilst the majority in flight over a single location were at 150–195 m above ground level, some reached altitudes of over 1100 m.^[88]

Many rove beetles have greatly reduced elytra, and while they are capable of flight, they most often move on the ground: their soft bodies and strong abdominal muscles make them flexible, easily able to wriggle into small cracks.^[89]

Aquatic beetles use several techniques for retaining air beneath the water's surface. Diving beetles (Dytiscidae) hold air between the abdomen and the elytra when diving. Hydrophilidae have hairs on their under surface that retain a layer of air against their bodies. Adult crawling water beetles use both their elytra and their hind coxae (the basal segment of the back legs) in air retention, while whirligig beetles simply carry an air bubble down with them whenever they dive.^[90]

Communication

Beetles have a variety of ways to communicate, including the use of

stridulate to communicate,^[91] but others may use sound to defend themselves when attacked.^[92]

Parental care

A dung beetle rolling dung

Parental care is found in a few families

asphyxiating, and protects them from the predatory carabid beetle Dicheirotrichus gustavi and from the parasitoidal wasp Barycnemis blediator, which kills some 15% of the larvae.^[94]

Burying beetles are attentive parents, and participate in cooperative care and feeding of their offspring. Both parents work to bury small animal carcass to serve as a food resource for their young and build a brood chamber around it. The parents prepare the carcass and protect it from competitors and from early decomposition. After their eggs hatch, the parents keep the larvae clean of fungus and bacteria and help the larvae feed by regurgitating food for them.^[95]

Some dung beetles provide parental care, collecting herbivore dung and laying eggs within that food supply, an instance of mass provisioning. Some species do not leave after this stage, but remain to safeguard their offspring.^[96]

Most species of beetles do not display parental care behaviors after the eggs have been laid.^[97]

Subsociality, where females guard their offspring, is well-documented in two families of Chrysomelidae, Cassidinae and Chrysomelinae.^{[98][99][100][101][102]}

Eusociality

Eusociality involves cooperative brood care (including brood care of offspring from other individuals), overlapping generations within a colony of adults, and a division of labor into reproductive and non-reproductive groups.^[103] Few organisms outside Hymenoptera exhibit this behavior; the only beetle to do so is the weevil Austroplatypus incompertus.^[104] This Australian species lives in horizontal networks of tunnels, in the heartwood of Eucalyptus trees. It is one of more than 300 species of wood-boring Ambrosia beetles which distribute the spores of ambrosia fungi.^[105] The fungi grow in the beetles' tunnels, providing food for the beetles and their larvae; female offspring remain in the tunnels and maintain the fungal growth, probably never reproducing.^[105][104] Cooperative brood care is also found in the bess beetles (Passalidae) where the larvae feed on the semi-digested faeces of the adults.^[106]

Feeding

Hycleus sp. (Meloidae) feeding on the petals of Ipomoea carnea

Beetles are able to exploit a wide diversity of food sources available in their many habitats. Some are

fungi - some beetles have yeasts living their guts, including some yeasts previously undiscovered anywhere else.^[108]

Decaying organic matter is a primary diet for many species. This can range from

carrion beetles, Silphidae). Some beetles found in dung and carrion are in fact predatory. These include members of the Histeridae and Silphidae, preying on the larvae of coprophagous and necrophagous insects.^[109] Many beetles feed under bark, some feed on wood while others feed on fungi growing on wood or leaf-litter. Some beetles have special mycangia, structures for the transport of fungal spores.^[110]

Ecology

A camouflaged longhorn beetle, Ecyrus dasycerus

Anti-predator adaptations

Beetles, both adults and larvae, are the prey of many animal

dragonflies, robberflies, reduviid bugs, ants, other beetles, and spiders.^[111][112] Beetles use a variety of anti-predator adaptations to defend themselves. These include camouflage and mimicry

against predators that hunt by sight, toxicity, and defensive behaviour.

Camouflage

Further information: Camouflage

Camouflage is common and widespread among beetle families, especially those that feed on wood or vegetation, such as leaf beetles (Chrysomelidae, which are often green) and weevils. In some species, sculpturing or various colored scales or hairs cause beetles such as the avocado weevil Heilipus apiatus to resemble bird dung or other inedible objects.^[111] Many beetles that live in sandy environments blend in with the coloration of that substrate.^[113]

Mimicry and aposematism

Clytus arietis (Cerambycidae), a Batesian mimic

of wasps

Further information: Mimicry and Aposematism

Some

aposematic, where bright or contrasting coloration warn off predators; many beetles and other insects mimic these chemically protected species.^[114]

aposematic

coloration, warning of their toxicity.