Beetles

Coleoptera

Summary 3

The Coleoptera /koʊliːˈɒptərə/ order of insects is commonly called beetles. The word "coleoptera" is from the Greek κολεός, koleos, meaning "sheath"; and πτερόν, pteron, meaning "wing", thus "sheathed wing", because most beetles have two pairs of wings, the front pair, the "elytra", being hardened and thickened into a sheath-like, or shell-like, protection for the rear pair, and for the rear part of the beetle's body. The superficial consistency of most beetles' morphology, in particular their possession...

Associations 4

Fungus / infection vector
Basidiobolus ranarum is spread by Coleoptera

In Great Britain and/or Ireland:
Fungus / feeder
Coleoptera feeds on spore mass of fruitbody of Phallus hadriani

Plant / pollenated
adult of Coleoptera pollenates or fertilises flower of Coeloglossum viride

Plant / pollenated
adult of Coleoptera pollenates or fertilises flower of Dactylorhiza fuchsii

Plant / pollenated
adult of Coleoptera pollenates or fertilises flower of
Other: major host/prey

Animal / pathogen
colony of Hirsutella anamorph of Cordyceps entomorrhiza infects Coleoptera

Animal / associate
larva (1st year) of Dinoptera collaris is associated with disused wood-boring galleries of Coleoptera

Animal / pathogen
Entomophthora coleopterorum infects larva of Coleoptera

Animal / predator
nymph of Orthotylus tenellus is predator of egg of Coleoptera

Animal / predator
leaf of Pinguicula vulgaris is predator of adult of Coleoptera
Other: minor host/prey

Animal / predator
adult of Troilus luridus is predator of adult of Coleoptera

Characteristics 5

The most distinctive feature of beetles is the hardening of the forewings into elytra; it is from this that they get their formal name (koleos - sheath, pteron - wing). The elytra serve to protect the more delicate hind wings, as well as the dorsal surface of the abdomen, and may have been a key factor allowing them to exploit narrow passageways (for example, in leaf litter and under bark). During flight the forewings are opened enough to allow the hind wings to unfold and function:

Other derived characteristics of beetles are:

  • hind wings folded under elytra, with reduced venation
  • hind two thoracic segments (mesothorax+metathorax=pterothorax) broadly connected with abdomen, so that the primary functional units of body are head / prothorax / pterothorax + abdomen, rather than the more typical head / thorax / abdomen of many other insects.
  • genitalia retracted into abdomen
  • adult antenna with 11 articles

Beetles are holometabolous insects, normally with adecticous, exarate pupae. Most species have chewing mouthparts. There is a gula present on the undersurface of the head.

Coleoptera overview 6

Order Coleoptera has the most insect species.  Beetles can be found throughout the world and can vary from a millimeter to 75 millimeters in length.  They have an open circulatory system that uses fluid instead of blood.  Most beetles have two pairs of wings, one pair is hardened and the other pair is membranous.  Their antennae are mostly used for their sense of smell.  They have spiracles, which are breathing holes on their abdomen.  Most beetles feed on plants, but other species are predaceous.  Some species are aquatic and have a hard exoskeleton.  Some species are sexually dimorphic.  This can be seen when males have horns on their head.  Most beetles undergo complete metamorphosis.  They go through several stages from: the egg, the grub, the pupa, and the adult (also known as an imago).  Most beetles have a gland that produces pheromones to attract a mate.  Beetles can be found in the fossil record as far back as the Lower Permian.  People release beetles to control common pests, for instance, ladybugs are released into gardens to control aphid populations. 

Communication and perception 7

Most beetles communicate with other beetles with chemicals. Males often locate females by their scent. Beetles usually can't see very well. Some beetle make sounds, usually scraping their mouthparts together or rubbing their legs on their bodies. Some beetles that live in dead wood drum and make vibrations. "Fireflies' and "lightning bugs' are actually beetles. They glow in the dark to communicate.

Conservation status 8

Most beetle species are abundant, and don't need to be especially conserved. Beetles that live in habitats that are getting changed or wiped out could be in trouble, and some beetles depend on certain plant species. If the plant goes, they go. There is a species of aquatic beetle that only lives in a few rivers in northern Michigan. It is considered endangered.

Development 9

Beetles have four different stages in their life cycle. Adult female beetles mate and lay eggs. The eggs hatch into a larval stage that is wingless. The larva feed and grow, and eventually change into a pupal stage. The pupa does not move or feed. Eventually the pupa transforms into an adult beetle.

Development - Life Cycle: metamorphosis

Ecosystem roles 10

Beetles have lots of roles. Dung beetles help get rid of waste, beetles that eat wood help break down dead trees, some beetles feed on pollen and help pollinate flowers.

Ecosystem Impact: pollinates; biodegradation

Food habits 11

Beetles eat all kinds of food. Most are specialists in few kinds, but some, like ground beetles, eat lots of things. Most beetles eat plant parts, either leaves or seeds or fruit or wood. Many are predators on other small animals. Some eat fungus, and there are a bunch of species that eat dung. Sometimes the larvae eat different foods than the adults do.

Functional adaptation 12

Wings fold multiple times without wear: beetles
 

Wings of beetles fold multiple times without wear or fatigue by having resilin in key joints. 

   
  "Beetles use their fore-wings for a different purpose altogether. These creatures are the heavy armoured tanks of the insect world and they spend a great deal of their time on the ground, barging their way through the vegetable litter, scrabbling in the soil or gnawing into wood. Such activities could easily damage delicate wings. The beetles protect theirs by turning the front pair into stiff thick covers which fit neatly over the top of the abdomen. The wings are stowed neatly beneath, carefully and ingeniously folded." (Attenborough 1979:79)


"This account shows the distribution of elastic elements in hind wings in the scarabaeid Pachnoda marginata and coccinellid Coccinella septempunctata  (both Coleoptera). Occurrence of resilin, a rubber–like protein, in  some mobile joints together with data on wing unfolding  and flight kinematics suggest that resilin in the  beetle wing has multiple functions. First, the distribution pattern of  resilin  in the wing correlates with the particular folding  pattern of the wing. Second, our data show that resilin occurs at the  places  where extra elasticity is needed, for example in  wing folds, to prevent material damage during repeated folding and  unfolding.  Third, resilin provides the wing with elasticity in  order to be deformable by aerodynamic forces. This may result in  elastic  energy storage in the wing." (Haas et al. 2000:1375)
  Learn more about this functional adaptation.

Functional adaptation 13

Insect elytra resist shear and cracking: beetles
 

Elytra of beetles maintain integrity of their two layers by transforming forces through connecting bio-nails. 

     
  "Nature is replete with examples of layered-structure materials that are evolved through billions of years to provide high performance. Insect elytra (a portion of the exoskeleton) have evoked worldwide research attention and are believed to serve as fuselages and wings of natural aircraft. This work focuses on the relationship between structure, mechanical behavior, and failure mechanisms of the elytra. We report a failure-mode-optimization (FMO) mechanism that can explain elytra's mechanical behaviors. We show initial evidence that this mechanism makes bio-structures of low-strength materials strong and ductile that can effectively resist shear forces and crack growth. A bio-inspired design of a joint by using the FMO mechanism has been proved by experiments to have a potential to increase the interface shear strength as high as about 2.5 times. The FMO mechanism, which is based on the new concept of property-structure synergetic coupling proposed in this work, offer some thoughts to deal with the notoriously difficult problem of interface strength and to reduce catastrophic failure events." (Fan et al. 2005:229)
  Learn more about this functional adaptation.

Geographic range 14

Beetles are the most diverse group of insects. There are over 300,000 species known to science, and probably many tens of thousands more still unknown. Beetles are found on land and in fresh water all over the world.

Biogeographic Regions: nearctic (Introduced , Native ); palearctic (Introduced , Native ); oriental (Introduced , Native ); ethiopian (Introduced , Native ); neotropical (Introduced , Native ); australian (Introduced , Native ); oceanic islands (Introduced , Native )

Habitat 15

Beetles are found in just about every habitat. Most species live on plants, others tunnel or burrow, some swim.

Habitat Regions: temperate ; tropical ; polar ; terrestrial ; freshwater

Terrestrial Biomes: tundra ; taiga ; desert or dune ; chaparral ; forest ; rainforest ; scrub forest ; mountains

Aquatic Biomes: lakes and ponds; rivers and streams

Wetlands: marsh ; swamp ; bog

Introduction 16

The Coleoptera, or beetles, includes many commonly encountered insects such as ladybird beetles (family Coccinellidae), click beetles (Elateridae), scarabs (Scarabaeidae), and fireflies (Lampyridae). They live throughout the world (except Antarctica), but are most speciose in the tropics.

The oldest beetle fossils are from the Lower Permian (about 265 million years old; Ponomarenko, 1995); since then the group has diversified into many different forms. They range in size from minute featherwing beetles (Ptiliidae), adults of which are as small as 0.3 mm long, to the giant Goliath and Hercules beetles (Scarabaeidae), which can be well over 15 cm. While most species are phytophagous, many are predacious, or fungivores, or are parasitoids. They communicate to one another in many ways, either by use of chemicals (e.g. pheromones), sounds (e.g. stridulation), or by visual means (e.g. fireflies). They live in rainforest canopies, the driest deserts, in lakes, and above treeline on mountains.

In one sense the most unusual property of beetles is not some aspect of their structure or natural history, but their sheer number. There are more known species of Coleoptera than any other group of organisms, with over 350,000 described species. Perhaps the most famous quote about beetles comes from the great population geneticist J.B.S. Haldane, who was asked what might be learned about a Creator by examining the world. His response: "an inordinate fondness for beetles" (Fisher, 1988).

Known predators 17

Coleoptera is prey of:
Amia calva
Nematocera imagines
Passerina cyanea
Hylocichla mustelina
Geothlypis trichas
Picoides pubescens
Baeolophus bicolor
Vireo olivaceus
Melanerpes erythrocephalus
Hymenoptera
Sitta pygmaea
Dendroica coronata
Phrynosoma
Sialia
Junco hyemalis
Spizella passerina
Turdus migratorius
Leucosticte atrata
Anthus spinoletta
Eremophila alpestris
Scolopacidae
Araneae
Cicindelidae
Camponotus pennsylvanicus
Rodentia
Serpentes
Varanidae
Erinaceus europaeus
Vulpes vulpes
Calcarius mccownii
Calcarius ornatus
Spermophilus
Calamospiza melanocorys
Asilidae
Peromyscus maniculatus
Orthoptera
Athene cunicularia
Salvelinus fontinalis
Saurothera vieilloti
Otus nudipes
Amphisbaena caeca
Herpestes auropunctatus
Eleutherodactylus coqui
Eleutherodactylus richmondi
Eleutherodactylus portoricensis
Eleutherodactylus wightmanae
Eleutherodactylus eneidae
Eleutherodactylus hedricki
Melanerpes portoricensis
Todus mexicanus
Mimocichla plumbea
Margarops fuscatus
Anolis cuvieri
Anolis evermanni
Anolis stratulus
Anolis gundlachi
Myiarchus antillarum
Vireo latimeri
Nesospingus speculiferus
Icterus dominicensis
Vireo altiloquus
Seiurus aurocapillus
Seiurus motacilla
Sphaerodactylus klauberi
Sphaerodactylus macrolepis
Diploglossus pleei
Bufo marinus
Chlorostilbon maugeus
Anthracothorax viridis
Mniotilta varia
Parula americana
Dendroica caerulescens
Dendroica discolor
Setophaga ruticilla
Coereba flaveola
Loxigilla portoricensis
Typhlops rostellatus
Odonata
Gonatista grisea
Hemiptera
Coleoptera
Diptera
Eptesicus fuscus
Pteronotus parnelli
Spindalis zena
Falco sparverius
Tyrannus dominicensis
Elaenia
Dendroica petechia
Loxigilla noctis
Trochilidae
Anolis gingivinus
Anolis pogus
Chilopoda

Based on studies in:
USA: Florida, South Florida (Swamp)
Russia (Agricultural)
USA: Illinois (Forest)
USA: Arizona (Forest, Montane)
USA: Montana (Tundra)
India, Rajasthan Desert (Desert or dune)
USA: California, Cabrillo Point (Grassland)
Puerto Rico, El Verde (Rainforest)
USA: Alaska (Tundra)
Canada: Ontario, Mad River (River)

This list may not be complete but is based on published studies.

Known prey organisms 18

Coleoptera preys on:
Plectoptera
Odonata
Hemiptera
Psectrocladius
Rotifera
Cladocera
Chironomidae
detritus

alpine vegetation
Diptera
Eleucine
Cyperus
Cenchrus
Artemisia frigida
Bouteloua gracilis
Oenothera laciniata
Psoralidium tenuiflorum
Hesperostipa comata
Heterotheca canescens
Aristida purpurea
Carex
Gutierrezia
Ratibida columnifera
Ericameria nauseosa
Cleome serrulata
Liatris punctata
Atriplex canescens
Thelesperma filifolium
Coleoptera
Acari
Collembola
Isoptera
live leaves
live wood
roots
pollen
fruit
seeds
flowers
fungi
Isopoda
nectar and floral
leaves
wood
Miniopterus australis

Based on studies in:
USA: Florida, South Florida (Swamp)
Russia (Agricultural)
Puerto Rico, El Verde (Rainforest)
USA: Illinois (Forest)
USA: Arizona (Forest, Montane)
USA: Montana (Tundra)
USA: California, Cabrillo Point (Grassland)
USA: Alaska (Tundra)
India, Rajasthan Desert (Desert or dune)

This list may not be complete but is based on published studies.

Lifespan/longevity 19

Most beetle species complete their lives in a single year. Some, especially larger ones, live for more than a year, hatching in summer, a few months to a year or more as a larva and pupa, and then emerging to reproduce as an adult.

Physical description 20

Beetles are like all insects, they have a head, thorax, and abdomen, and six legs. Their bodies tend to be very solid and tough. They have chewing mouthparts and often have powerful jaws. Adult beetles have modified wings: the first pair of wings is small and very hard, and acts as a protective covering for the second pair of wings. Many beetles can fly with their second pair of wings. Most adult beetles are brown or black, but some are very brightly colored. Beetle larvae look sort of like worms, but they have six legs and a hard head. Beetle pupa can't move and are covered with a leathery skin.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; polymorphic ; poisonous

Sexual Dimorphism: sexes alike; female larger; male larger; sexes colored or patterned differently; sexes shaped differently; ornamentation

Pollinator 21

Early beetles appear to have been among the primary visitors of primitive flowering plants. An improvement over wind pollination, beetles likely played an important role in the evolution of flowering plants.

Many familiar North American plants are pollinated by beetles. For example, plants in the magnolia family, including the eight species that are native to the United States, have flowers that are specialized for beetle pollination. In fact, though magnolia flowers are often described as "primitive" (relatively unchanged from the ancestral type), some researchers have suggested that magnolia flowers are actually quite specialized and have evolved to promote nearly exclusive pollination by beetles. The beetles appear to be attracted by the odor of the flowers - which is sometimes described as unpleasant - as well as their color. They feed on nectar, stigmas, pollen, and secretions of the petals. Other insects appear to be unable to access magnolia flowers at critical times, while stigmas are mature or while pollen is shed. At least some magnolia species, including one species in Mexico, produce heat.

Odor, often foul or unpleasant, is thought to act as a primary attractant for many beetle and fly pollinators. Beetle-pollinated plants additionally produce heat. The odor may mimic a food source; the heat is thought to help spread the odor and/or provide a direct energetic benefit to pollinating insects

Predation 22

Most beetles hide, and many beetle larvae dig tunnels to hide in. Some rely on their hard shell. Some, like lady beetles, have toxic chemicals to repel predators. Some can bite. Some, like ground beetles, run fast.

Known Predators:

  • Talpidae
  • Soricidae
  • Sigmodontinae
  • Muridae
  • Mephitis mephitis (like beetle larvae)
  • Piciformes
  • other Aves 
  • Anura
  • Anura
  • Caudata
  • other Coleoptera 
  • Actinopterygii
  • Hymenoptera
  • Formicidae
  • Araneae (when they can bite through the shell)

Reproduction 23

Mating System: monogamous

Female beetles usually lay dozens or hundreds of eggs. Reproduction is often timed to match the time of most available food.

Breeding season: Breeding season varies, often in spring or summer

Key Reproductive Features: semelparous ; iteroparous ; seasonal breeding ; year-round breeding ; sexual ; fertilization (Internal ); ovoviviparous ; oviparous

Adult beetles mate, and the female lays eggs on or very near a food source for her larvae. Some beetles collect a supply of food for their larvae, and lay the egg in the ball of food. Some scavenger beetles even feed their babies.

Parental Investment: no parental involvement; male parental care ; female parental care

The suborders of coleoptera 24

The four living suborders of beetles diverged from one another in the Permian and early Triassic, and are substantially different from one another. Adults differ in the structure of the prothorax, hind wing, abdomen, ovary, testes, and so on. The major differences are summarized in a table.

Polyphaga is by far the largest suborder, containing 85% of the known species, including rove beetles, scarabs, stag beetles, metallic wood-boring beetles, click beetles, fireflies, blister beetles, mealworms, ladybirds, leaf beetles, longhorn beetles, and weevils. Many are phytophagous. Adephaga includes ground beetles, tiger beetles, predacious diving beetles, and whirligig beetles; most adephagans are predacious. Myxophaga is a small suborder, containing less than 100 known species, whose members are small or minute, and associated with hygropetric habitats, drift material, or interstitial habitats among sand grains. Archostemata contains several families of beetles, most associated with wood; members of this family are somewhat similar to some of the earliest, Paleozoic beetle fossils.

Sources and Credits

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