SCIENCE REPORTER, JANUARY 201129

WHEN theologians asked thefamous biologist JBS Haldane,‘what could be inferred about

the mind of the Creator from the works ofHis creation’, he quipped in jest: “TheCreator, if he exists, has a specialpreference for beetles.” True. The livingworld is predominated by various kinds ofbeetles – small, big, stout and slim. Noother group of animals exhibits such arange of size, colour and shape. Imagine,one in four species in the world is a beetleand they account for 40% of all knowninsect species. How come the world isfull of beetles?

Though known from earlier times,beetles were classified and describedsince 1871 and till now scientists havedescribed about 3,50,000 types.Entomologists (scientists who study insects)claim that the true number of beetlescould probably be about a million. Not amonth passes without the discovery of anew beetle species. In fact, befitting thebicentennial celebration of Darwin, a newdung beetle species found in the remoteforest region of Costa Rica was namedafter Darwin – Canthidium (Eucanthidium)

darwini in 2009.

Scientists identify beetles byColeoptera, which means ‘sheathedwings’. Though they have wings beetleshardly fly and some like ground beetleshave lost their ability to fly completely. Likeother insects they also have three-segmented body and six legs. The uniquefeature of beetles is the exoskeleton madeup of large number of, and particularlyhard, forewings that act like armour.

Since there are more than 3,50,000varieties of beetles, obviously they mustcome in various shapes and sizes. One ofthe smallest beetles is the fringed antbeetle (Nanosella fungi) that is just 0.25mm in length. In fact at these lengths theywould be smaller than many single celledprotozoa. In contrast, the world’s largestbeetles Titanus giganteus and Callipogon

armillatus are palm full; these can be aslarge as an adult human palm. Anotherlarge beetle Goliathus giganteus couldgrow to a body length up to 10 cm.

When Australian tiger beetle(Cicindela hudsoni) is chasing, the preyknows that it cannot show a clean pair ofheels ever. This beetle is the world’s fastestrunning insect; it can run as fast as 9 km/h.It chases down the prey at high speed.The heaviest and bulkiest beetles are theMegasoma beetles of South America. Theheaviest species is Megasoma actaeon

whose fully grown larva can weigh over200 g. While most of the insects live for ashort duration, Jewel beetles can survivefor 30 years or more. The Bombardierbeetle can shoot boil ing hot puffs ofirritating gas from its anus, which the beetlecan aim with remarkable accuracy andturn on and off 500 times a second.

As the name suggests, the strongestcreature in the world is the Hercules Beetle;it can carry up to 850 times its own weight.In contrast, a huge African elephant canonly carry up to 25% of its own weight onits back. In a laboratory experiment, it wasfound that the Hercules beetle could pullabout 850 times its own body weight,equivalent to an average adult (70 kg) liftingseven tractors.

Eat Everything - AnythingIf beetles had to evolve in various diverseforms they must have adapted andspecialised to feed on any available food,indeed all organic material. Beetles suchas red flour beetle are stored food pestsand live all their life in the stored food grains.They do not have normal eyesight but areexceptionally good at detecting the lightsource. Living under sack full of grains theyneed to know when they are leaving thestored grains. On the other hand, somebeetles such as ladybug have pretty good

T.V. VENKATESWARAN

Beetles of

the World

Beetles of

the WorldBeetles come in all shapes and sizes, and, of

course, in great numbers too!

Click beetle

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eyesight. They are called friends of plantsas they feed upon pest insects such asspider mites and aphids and thus protectthe plants.

Leaf beetles, as the name suggests,are herbivores and cause havoc to plantsand crops. Various specialised beetlesadapted to feed on the roots, stems,leaves, or reproductive structures of theirhost plants have also evolved. Somespecies live on fungi, others burrow intoplant tissues, and still others excavatetunnels in wood or under bark.

Ground beetles or carabids arecarnivorous and devour earthworm andsnails while beetles like Staphylinidae,Amblyopininae are parasites on mammals.A class of beetles are scavengers; they feedon carrion, faecal material, decayingwood, or other dead organic matter. Dungbeetles as the name suggest eat dung ofother animals. Dung beetles, such as the

Horns of Beetles

What makes beetles unique in theinsect world is their ability to growhorns. Horns at times are about onethird of the entire body weight. Studieshave found that beetles use their hornsin surprising ways.

Science today has pretty good ideaof what needs to happen for legs tobecome longer or wings to become wider. But scientists are still baffledhow animals develop a completely new body part. Studying how beetle hornsevolved might help answer the question.

A beetle horn is not a horn. Some beetle horns snap together, likepincers. Others are low and curved, like an elephant’s tusk. And watchout—a dung beetle’s horns can be longer than the rest of its body. Beetlehorns come in a variety of shapes and sizes. Often, just like male elephanttuskers, it is only mostly males that have fully grown adult horns. Formales the horns are weapons to keep off other males from approaching thefemale in the tunnel-nest. Beetles use their horns to grab other beetles, liftthem in the air, and even throw them off trees. Sometimes a beetle willslide its horn underneath another beetle and flip it over.

The horn in adulthood is used as a weapon; it is used to break thehead capsule when the beetles are in juvenile stage. Larvae of beetlesnormally grow inside little balls of packed dung, called brood balls. Insidetheir cozy brood balls, the larvae grow thick and protective helmets calledlarval head capsules. But the larvae eventually have to break out of thesecapsules to become full-grown adults. Larvae seem to use their horns topoke their way out of their capsules. To test this hypothesis, in some of thelarva, scientists used electricity to destroy the horn. This stopped the hornsfrom growing normally. Sure enough, these hornless larvae could not shedtheir head capsules, thus establishing the purpose of the horns.

African Garreta nitens, use their serratedforeleg and broad hoe-like head to carveout chunks of faecal material to use it asfood. They ingest huge quantities of dung,using their membranous mandibles to strainout remnants of undigested food, bacteria,yeasts, and moulds. Not even a scrap offood is allowed to go waste. Dung beetleshave a crucial role in nature as they

In fact humans have beenusing beetles since thedawn of civilisation.A class of beetles calledjewelled beetles have ametallic shine anddazzling colours in theirexoskeleton.

Potato beetle

Rhino beetle

Beetal Colours

Tortoisebeetle

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consume waste and bury the organicmatter in the ground; they contribute to soilfertility and structure.

The Great SurvivorsFossils indicate that beetles originated wayback on the geological time scale, awhopping 299 million years ago—waybeyond the age of dinosaurs. They havebeen diversifying since then. How andwhen the large number of beetles cameabout has been an intriguing question.Whether beetles diversified into numerousspecies from a handful of original ancestralspecies, or whether there were quite a fewancestral species that gave way tocopious beetle species that we witnesstoday has been a hotly debated topic formany decades, but never resolved.

The astonishing diversity of beetleswas hitherto attr ibuted to herbivory—feeding on plants. Biologists speculatedthat the huge diversification occurred withthe emergence of flowering plants some140 million years ago. As newer species offlowering plants emerged, newer types ofbeetle species co-evolved to feed on theroots, leaves, and flowers of the plants.

However, a recent study done withmodern techniques of DNA analysis

indicates that large numbers of modern-day beetle lineages evolved very soonafter the first beetles originated, and havepersisted ever since. After millions of years,many diverse lineages appeared duringthe Jurassic period, when the majorgroups of dinosaurs appeared too. Thestudy used the DNA sequencing and fossilrecords to compile a comprehensiveevolutionary ‘ family tree’ for beetles. Bycomparing DNA sequences from 1,880beetle species, the scientists were able togroup beetle species that havedescended from a common ancestor,enabling them to build an evolutionarytree for all the species included.

From the study it appears that the largenumbers of beetle species existing todayare the direct result of this early evolutionimplying that there has been a very highrate of survival and continuousdiversification of many lineages. Evolutionof many modern beetle l ineagessignificantly predates the appearance ofthe first flowering plants. Beetles havedisplayed an exceptional ability to seizenew ecological opportunit ies anddevelop a great range of life styles andfeeding types; not just feeding on greenplants. In contrast many other species suchas dinosaurs have vanished from the faceof earth without trace, making beetles thegreat survivors.

To Be or Not to BeSurvival in terms of evolution impliesadaptations. Beetles appear to be apt atit. Two recent studies indicate how beetlessize up opportunity to evolve into diversevariety of species and thus survive the greatgame of evolution.

A class of beetles called carabidbeetles feeds on insects, worms and snails.Snails are juicy food for them; but snailshave a hard shell protecting them. To relish

the snail the beetles have to either have alarge powerful head with which they cancrush the snail shell or the head should besmall enough such that it can be insertedinto the shell mouth. Beetles have evolvedboth ways. There are both elongate, small-headed and stout, large-headed carabidbeetles that feed upon land snails.

Large-headed beetles can readilycrush snail shells with their powerful jaws,but cannot insert their oversized heads intothe shells. In contrast, small-headed beetlescan insert their heads into the shells fordirect predation on snail bodies, but poorlycrush the shells because of their frugal jaws.Carabid beetles that feed on snails tendto have an extremely slender or stoutforebody compared to beetles that eatinsects and earthworms. Studies indicatethat adaptations for snail feeding led tothe diversification of beetle heads.

If beetles have evolved and diversifiedto both crush the shells and protrude insidethe shell, snails have counter evolved anddiversified. It has been demonstratedamong the fresh water snails that the shellmorphology (shape) has diversified alongwith the diversif ication of beetles.Freshwater snails have now two types ofshells – elongate and round. The elongateshells protect against entry attacks androunded shells protect against crushingattacks.

Speciation has occurred in beetlesover a considerable period of t ime.Diversity in beetle species can occurbecause of their varied feeding habitats.Scientists have recently noticed that aparticular leaf beetle is in the process ofspeciation. Two beetle species havediversified, one specialising in feedingmaple tree leaf and the other the leaf ofwil low. Both beetles are visuallyindistinguishable but each prefers to feedand lay eggs on its own “host plant”.

Stag beetle

Lady Bird beetle Colourful beetle

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Although there is some intermixing, thebeetles show a decided preference formates from the same host. Scientists haveobserved that the willow beetles starve todeath rather than feed on the mapleleaves readily consumed by their maplebeetle cousins. Thus, slowly and steadily inthousands of years both will divide into twoseparate species—this is evolution inaction, and emergence of biodiversity.

These studies have established howecological factors contribute toevolutionary divergence and the origin ofEarth’s millions of species. This reflects thetrue power of natural selection, which hasdriven these beetles to become sointimately adapted to their host plantenvironment, promoting their speciation

along the way. It is not a coincidence thatplant-feeding insects, such as beetles, areamong the most ecologically specializedand the most species-rich groups on theplanet.

A Lesson or TwoThe Hercules beetle has a trick up itssleeve. This amazing beetle, usually foundin the rainforests of Columbia, Venezuela,Peru, Ecuador, Bolivia, and Brazi l, ismysterious – it can change the colour ofits exoskeleton as it rains. The insect’sexoskeleton or shell changes from greento black as its surrounding atmosphere getsmore humid. Scientists have been able toshed light on this mysterious phenomenononly recently.

Scanning electron microscopy hasbeen utilized to study the minute structureof the exoskeleton andspectrophotometer has been used toanalyze how the light interacts with thisstructure. The shells, the study reveals, arenot green dyed. When the light interfereswith the structure it produces the typicalgreen colour of the shell, through aprocess called irradiance. However, whenwater penetrates through the widely openporous layers, it destroys the interferencephenomenon leading to blackcolouration.

As to why the beetle changes colour,questions remain. Some have suggestedthat the phenomenon occurs for defenceand protection. At night the weather is

humid. Therefore, it is good to turn black.Others have suggested that it is to do withwarmth absorption at night.

Nevertheless, scientists say that theycould use the knowledge gained fromstudying Hercules beetle to design‘intelligent’ materials’. Such materials couldbe put to work as humidity sensors. Thiscould be useful for example to monitorthe moisture level in food processingindustry etc.

In fact humans have been usingbeetles since the dawn of civilisation. Aclass of beetles called jewelled beetleshave a metallic shine and dazzling coloursin their exoskeleton. The durability andcolour of the beetle exoskeleton hasinspired their use in jewellery. AmazonianIndians have been long since using shellsfrom buprestid beetle, Euchroma

gigantean, to make jewellery. A Spanishbeetle Lytta vesicatoria is the source ofchemical cantharadin used byveterinarians as a mating stimulant whenbreeding cattle and in the treatment ofcertain urogenital diseases

Beetles have also been objects ofworship! Early Egyptians perceived theEarth as a ball of dung pushed throughthe universe by a dung beetle, and usedthis beetle as the image for their sun god,Khepera.

Mr T.V. Venkateswaran is a scientist at VigyanPrasar, A-50, Institutional Area, Sector-62, Noida-201307, U.P. Email: tvv@vigyanprasar.gov.in

Amazonian Indians have beenlong since using shells frombuprestid beetle, Euchromagigantean, to make jewellery.

There are more than 3,50,000 varieties of beetles, obviously theymust come in various shapes and sizes. One of the smallest beetlesis the fringed ant beetle that is just 0.25 mm in length.

Tiger beetle

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