BBC Wildlife Magazine - - Beetles -

Aris­to­tle is cred­ited with coin­ing the term Coleoptera, the name we still use to­day for the bee­tle in­sect or­der. From the Greek words koleos (‘sheath’) and pteron (‘wing’), it sums up bee­tles’ most suc­cess­ful in­no­va­tion – wing cases, or ely­tra. Th­ese are tough­ened and of­ten ridged or cor­ru­gated. In ad­di­tion, they are curved to fit neatly to­gether, snug over the ab­domen, pro­tect­ing the del­i­cate mem­bra­nous hind wings furled be­neath. But with the flick of a few mus­cles, the ely­tra hinge for­wards, large hind wings un­flap and the bee­tle is air­borne.

The first beet­loids evolved from an an­ces­tor they shared with the lacewings, and the ear­li­est bee­tle fos­sils, which date from about 300 mil­lion years ago, had more flat­tened, wing-like, ill-fit­ting ely­tra. Th­ese pri­mor­dial wing-cases show a dis­tinc­tive net-like trac­ery of ridges and struts. To­day, mem­bers of the prim­i­tive bee­tle fam­ily Cu­pe­di­dae still have this ar­chaic ely­tral re­in­force­ment.

The other ma­jor ar­moured com­po­nent of a bee­tle’s body is the broad shield be­hind the head. Called the tho­rax by the unini­ti­ated, this is re­ally just the up­per plate of the first seg­ment of the tho­rax, yet it dom­i­nates the bee­tle’s fore­body. En­to­mol­o­gists re­fer to it as the prono­tum. Its domed, flat­tened or flanged form com­bines with the ely­tra to give bee­tles their sleek out­line. For mil­lions of years, this is what has en­abled them to hide in tight cran­nies or un­der loose bark or logs, or to push into root thatch, soil, car­rion, dung or be­tween the gills of mush­rooms.


If we know lit­tle about bee­tles, we know even less about their lar­vae – yet it is the grubs that do the eat­ing and grow­ing. At the end of its ‘lar­va­hood’, a bee­tle mag­got un­der­goes a mag­i­cal trans­for­ma­tion, in which most of its in­ter­nal or­gans are dis­solved and re­assem­bled to cre­ate the com­plete, fin­ished, winged adult. This process takes place in the pupa, or chrysalis, and is called holometabolism (com­plete meta­mor­pho­sis). It is in stark con­trast to the grad­u­ally in­creas­ing nymph growth of in­sects such as grasshop­pers, leaf bugs, cock­roaches and ear­wigs, which show hemimetabolism (in­com­plete meta­mor­pho­sis).

This split be­tween a seden­tary, self-feed­ing em­bryo stage and an ac­tive adult stage that dis­perses by flight is another of the bee­tles’ se­crets of suc­cess. Be­cause th­ese in­sects have di­vided their life his­to­ries into two halves, the adult bee­tles of­ten live ac­cord­ing to dif­fer­ent sea­sonal time frames, and in com­pletely dif­fer­ent habi­tats or eco­log­i­cal niches to their lar­vae. They thus neatly avoid the of­ten-crush­ing pres­sure of com­pet­ing with their own off­spring. For in­stance, the lar­vae of the vine wee­vil, Otiorhynchus

sul­ca­tus, are sub­ter­ranean root­feed­ers, whereas the adults live in trees, nib­bling leaf mar­gins into dis­tinc­tive stamp-edge per­fo­ra­tions.

The fat oil beetl ee­tles that wad­dle about Bri­tain’sBrit chalk downs, grassy banks nks and sandy un­der­cliffs are an­oth­erer ex­am­pleex of bee­tles with dra­mat­i­cally split per­son­al­i­ties.per Dur­ing their lum­ber­ing per­am­bu­la­tions, ns, the adults might chew a but­ter­cup leaf or two,, butbu their lar­vae live in a par­al­lel uni­verse. The many y thou­sands of oil bee­tle eggs hatch into tiny ag­ile lar­vae called tri­un­gulins, which race up plant stems and flow­ers to cling to fly­ing in­sects. A few lucky ones will at­tach to a fe­male soli­tary bee and get taken back to her small nest bur­row in the warm soil, where they trans­form into a sec­ond lar­val stage – le­g­less blobs that start de­vour­ing bee grubs and nec­tar and pollen stores.


At an im­plau­si­ble 0.3mm long, the Bo­li­vian feather-wing bee­tle, Scy­dosella mu­sawasen­sis, could scurry around quite hap­pily within this let­ter ‘O’. It is smaller than many sin­gle-celled an­i­mals. At the other end of the spec­trum, the huge Brazil­ian longhorn, Ti­tanus gi­gan­teus, may reach nearly 17cm and will only just sit in the fully ex­tended palm of your hand; if goaded, it can break a pen­cil in its jaws. This gives a size dif­fer­en­tial of at least 130 mil­lion times. Other gi­ants in­clude the shorter but bulki­ier go­liath bee­tles ( Go­liathus s) of Africa, at up to 11cm, and thee ele­phant bee­tles ( Me­ga­soma) of Sou­uth Amer­ica, which reach nearly 14cm.. But un­like the more fam­mil­iar mam­malian gi­ants, suchs as whales, whose li­ife in the oceans has al­lowwed them to evolve su­per­maas­sive size, aquatic bee­tles are much smaller than their ter­res­trial coun­ter­parts. The big­gest wa­ter bee­tle ever found – the ducal, Me­gadytes ducalis, of Brazil – is only 5cm long. This is for com­plex rea­sons, to do with the need for dif­fu­sional gas-ex­change gra­di­ents across small-bod­ied or­gan­isms that lack cen­tral lungs, heart and haemoglobin-based blood sys­tems to trans­port oxy­gen.

Most bee­tles, though, are at the diminu­tive end of the scale. The av­er­age across all known species is a frac­tion un­der 7mm. This does mean that some peo­ple have been put off study­ing the Coleoptera, in favour of big­ger, gaudier



En­cy­clo­pe­dias in­vari­ably make the claim that in­sects oc­cur from seashore to moun­tain-top. This, in fact, does not ap­ply to all in­sects – it does to bee­tles, though. A tiny flat-bod­ied ground bee­tle ( Ae­pus) in­hab­its silt-filled cracks in coastal rocks well below the high­wa­ter mark, which get cov­ered by the in­com­ing tide twice a day. Near the top of the world, North Amer­ica’s moun­tain bark bee­tle, Den­droc­tonus pon­derosae, munches pines as high as the tree-line.

Deep un­der­ground, some cave bee­tles have evolved tiny eyes or none at all, as well as long spindly legs and an­ten­nae to feel where they are go­ing, and have be­come flight­less (there’s nowhere to fly to). They eke out a liv­ing scav­eng­ing on the bits in bat guano, and any­thing else dead that they find in the dark­ness. In the karst lime­stone caves of south­ern Europe, Lep­todirus hochen­wartii in­cu­bates gi­ant eggs in­side its body that hatch into al­ready fully grown non-feed­ing lar­vae, which pu­pate quickly and emerge as adults.

Wa­ter bee­tles live in fresh wa­ter, but they re­main air breathers. Lack­ing gills, they visit the sur­face of­ten to re­plen­ish the oxy­gen car­ried in a thin air bub­ble known as a plas­tron. For bee­tles, ob­tain­ing oxy­gen from the air, by suck­ing it into fine tubes all along the body, is more ef­fi­cient than ab­sorb­ing it from wa­ter us­ing gills. Hav­ing made the leap to a ter­res­trial ex­is­tence from a marine one over half a bil­lion years ago, all in­sects had to com­mit to non-saline en­vi­ron­ments.


Bee­tles have chew­ing mouth­parts s, and so do their lar­vae. Th­ese are two tough, ap­prox­i­mately tri­an­gu­lar jaws, which are able to ex­ert pow­er­ful bit­ing or gr rind­ing pres­sure. There is vir­tu­ally nothin ng that bee­tles do not feed on.

As well as scav­eng­ing in leaf lit­ter, bee­tles eat plants from the roots to the shoots. They also tackle mam­mal dung, car­rion, other in­sects and even each other. They graze mould in com­post bins and are among the most im­por­tant com mpost­ing re­cy­clers when it comes to dead wood and fun­gal deca ay. Some steal food from spi­ders’ webs. A few species in­vade ourr homes to in­fest our stored food and eat our car­pets.

Bee­tles took ad­van­tage of the ex­plo­sion in plant di­ver­si­tyit with the evo­lu­tion of flow­er­ing plants 120–100 mil­lion years ago, and now are the sec­ond most speciose plant-feed­ing in­sects after moth cater­pil­lars. Many of the over 135,000 spe­cial­ist plant-feed­ers in the im­por­tant bee­tle lin­eage Phy­tophaga are ex­tremely host-spe­cific. They will feed only on a sin­gle plant species – and of­ten on just one part of that plant. In this way they have carved out tiny spe­cial­ist niches, al­low­ing di­ver­si­fi­ca­tion rather than com­pe­ti­tion with each other.

This does mean that some bee­tles have be­come se­ri­ous gar­den or crop pests. No­to­ri­ous ex­am­ples in­clude the lily bee­tle, Lil­io­cerislilii; the Colorado bee­tle,

Leptino­tarsa de­cem­lin­eata, which de­vours pota­toes; and the western corn root-worm, Diabrot­i­cavir­gifera, which at­tacks maize. How­ever, th­ese ‘bad guys’ are the ex­cep­tions.

A ten­lined June bee­tle from the USA shows off its tough wing-cases and mem­bra­nous flight wings.

Right: Her­cules bee­tles can be enor­mous, and the males sport im­pres­sive ‘horns’. Left: the ti­tan bee­tle, or Brazil­ian longhorn, is the world’s largest bee­tle. Liv­ing the he high life: black vine wee­vil vil adults nib­ble on tree leav aves, whereas the lar­vae feed onn root­sro un­der­ground. A Korowai man col­lects bee­tle lar­vae from a felled tree in Sen­dek, West Pa­pua, In­done­sia.

Above: a nut wee­vil in flight. Its lar­vae de­velop in hazel­nuts. Right: tiger bee­tles have long legs, which en­able them to move rapidly to catch prey.

Wa­ter bee­tles carry oxy­gen in an air bub­ble when they dive and can only be found in fresh wa­ter. Right: Eupho­lus nick­erli is a wee­vil of New Guinea’s mon­tane forests. Its jaws drill holes in plant stems or buds for its eggs.

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