Insecta (Insects))(Insects Introductory Article

Insecta (Insects))(Insects Introductory article

EA Jarzembowski, Maidstone Museum and Bentlif Art Gallery, Maidstone, UK Article Contents

.. Introduction

Insects are the most diverse organisms on Earth with a long evolutionary history and are .. KeyKey Stages in Insect Evolution

one of the most successful groups of organisms to have existed. .. InsectInsect Groups

.. GeneralGeneral Biology Introduction Judging by their diversity, insects (superclass Hexapoda) being a very large number of individuals. The upper size are perhaps the most successful organisms of alltime, with limlimitit of insinsectectss (e.(e.g.g. the HerHerculculeses beetle beetle 16 cm long) is an estimated 2–30 million species. Most of these are yet to ususuauallllyy atattritribubutedted to ththee coconsnstratrainintsts of ththeieirr spspeciecialal be described scientifically (only about a million have been (tr(tracheacheateate)) respirairator resp toryy system system (see below) below).. ApaApartrt frofromm namnameded sosofar)far)..HowHoweveever,r, alralreadeadyywelwellloveoverr370370000differ000differentent size, insects also have some special adaptations of their kinkindsds ofof beebeetletlehavhaveebeebeennrecorecognignizedzedcomcomparparededwithhaamer wit meree arthropod inheritance: quarter of a million flowering plants (angiosperms). The size of the task of documenting insect species is possibly .. ThTheireir bodbodiesies are segsegmenmentedted and the segmsegmentsents have becobecomeme fusfuseded and spespeciacializlizeded (tag(tagmosmosis)is) proproducducinging one ofofthe sinsinglegle bigbiggestgestchallellenge cha ngessfacifacingngentomo entomologlogististssinin threthreeemaimainnbodbodyydivdivisiisionsons ––aaheahead,d, thothoraxraxandandabdabdomeomenn the new millennium. Many insects have very specialized (( ).). lifestyles and are restricted to particular environments and Figure 1 microclimates. With the present rate of global develop- .. TheTheirir appappendendageagess (li(limbsmbs)) are compose composedd of sevseveraleral segsegmementntss anandd hahaveve bebecocomeme spspeciecialalizizeded to prprododucucee menment,t, itit isisperhaps perhapsineinevitvitablableethatmanythatmanyhabhabitaitatstswilllshri wil shrinknk or vanish during the twenty-first century and many species walking legs and other useful parts including several will become extinct. pairs of mouthparts and the sexual apparatus. .. They have a tough external skeleton (exoskeleton) to InsInsectsects occupy an impimportortantant rolrolee in terrestr terrestrialial and fresfreshwahwaterterecosys ecosystemtemssandandwitwithouhouttthethemmitit isisinconc inconceiveivablablee protect them and support the internal soft parts (see that the world’s food chains would survive in their present belbelow)ow).. The exoskeexoskeletletonon has the addaddeded funcfunctiotionn of of formform..ForForexamexampleple,,whawhattelselseewouwouldldpollinlinate pol atemanmanyyspecspeciesies redreducuciningg desdesiciccacatitionon whwhicichh hahass enenabableledd ininsesectscts toto of flofloweweriringng plplanants,ts, or prprovovididee fofoodod foforr many many smsmalalll successfully colonize the terrestrial environment. vertebrates? Some insects are injurious to human develop- menment,t, parparticticulaularlyrlyagriagriculculturturee(e.(e.g.g.locusts locusts))andandhealthlth hea (e.(e.g.g. Insects differ from other arthropods in that: malarimalaria-spreaa-spreadingding mosquitoes).mosquitoes). Such species species have been studied intensively by applied entomologists, but for every .. They have basically three pairs of legs, one pair on each pest there are thousands of harmless or beneficial species thoracic segment, and walk in a ‘tripodal’ manner. whiwhichchusuallallyyrece usu receivelessivelessatteattentintion.Thoseon.Thosethathattdodoareareofteoftenn .. They have have evolvelved evo d powpoweredered flight, unlikeunlike any othotherer colcolourourfulful,, such as butterfl butterfliesies,, or larlargege and activeive, act , liklikee dragonflies. Even small unobtrusive insects, however, may invertebrates. Over 99% of insects are winged or belong to to basically basically winged insect groups (collectively(collectively called have a fascinating biology which can provide insight into PterPterygoygotata or pterpterygoygotes,tes, see below) below).. UnlUnlikeike in othotherer the complexity of life. For example, the study of ants, animals, insect wings evolved independently of limbs wasps and bees has revealed much about the evolution of socsociaiallbebehahaviviouourrininwhicichhrea wh reariringng ththeeyoyoununggisis aacocommmmununalal responsibility. For many years, the Drosophila fruitfly has Mouthparts Antenna been a labora laboratorytory animaanimall for importa importantnt genetic genetic worworkk Compound eye including how genes control body development. Insects Thorax can thus help us to understandunderstand the workingsworkings of life itself..itself Forewing Why are insects so successful as a group? There is no simple answer, but it may be that they are about the right size, most insects ranging from a few millimetres to a few Hindwing cencentitimemetretress lolongng.. ThThee EaEartrthh cacann susupppporortt ononlyly a fefeww thothoususanandd spspeciecieses of lalargerge ananimimalalss susuchch as bibirdrdss anandd Legs

supportmammals. a lotAt ofthe microorganisms other end of the that scale, are the smaller planet th canan Abdomen insectsinsects,, but because their populationspopulations spread so easily,y, easil Figure 1 Giant antant Formicium showing insect body organization (after their biodiversity is correspondingly low – despite there Jarzembowski). Wingspan 144 mm.

Insecta (Insects)

anandd ththererefefororee wiwiththououtt lolossss of fufuncnctitionon in ototheherr appendages. Adult

Key Stages in Insect Evolution Egg Insects are thus distinguished by a number of important Grasshopper adaptations. Insects also have a long geological history. ThTheefofoururmamaininstastagesingesintheevoltheevolututioionnofofininsesectshadctshad alalreareadydy Nymph been accomplaccomplishedished by the close of the PalaeozoicPalaeozoic era (245 million years ago). These were: 1. The rise rise of pterygo pterygotete insectsinsects from somesome primitivtivelyelyprimi winglwinglessess insectsinsects (apterygotes,(apterygotes, see below).below). This helped Nymph didispspersersalal anandd escescapapee from from grgrououndnd enenememieiess (e.(e.g.g. spispiderders)s) priprioror to the evolutlution evo ion of any other flyingng flyi animals. 2. The abiliilityab ty of many insecinsectsts (Neopter(Neoptera,a, see below)below) to fold their wings over their bodies when at rest. This gave adult winged insects the advantage of entering Adult confined spaces such as nooks and crannies in rocks and plants. 3. The appearan appearancece of metmetamoamorphrphosiosis,s, especiallallyespeci y com-- com plepletete metamo metamorphrphosiosiss (holom (holometaetabolboly).y). Insects Insects thatt tha reach the latter evolutionary level undergo a major strustructucturalral reorga reorganiznizatiationon durduringing a resting resting (pupal (pupal)) stage between the juvenile and adult stages (Figure 2,, Egg right). Butterfly Pupa 4. 4. A near-near-modernmodern ecologecologicalical sspectrumpectrum of plant-feedplant-feedinging activiactivityty (herbivory)(herbivory) arising over one hundred millionmillion years before the spread of flowering plants (angiosperms).

HolHolomeometabtabolyoly enaenablebledd the aduadultlt (imago (imago)) and juveni juvenilele (larva) to evolve marked differences in form and lifestyle Larva andandthusexplothusexploititdifferen differenttnatnaturaurallresoresourcurceseswithou withouttmutmutualual comcompetpetitiition.on. ItIt isisperhap perhapssineinevitvitablableethatthatinsinsectsectspospossesssessinging FigFigure2ure2 Lifecycles ofof hemimhemimetabetabolous(left)olous(left)andholom andholometaboetabolouslous(rig(right)ht) insects compared (nymph = larva, pupa = chrysalis). (Adapted from a combination of neoptery and holometaboly (2 and 3) Chinery, 1993.) include the most diverse organisms on Earth. Complex adaadaptatptationionsssuchsuchasasparasiasitistismmand par andsocsocialialityityappappeareareded latlaterer shared genetic characters at the molecular level. There are, inin ththeeMeMesozsozoioicceraera(th(theeagageeofof ththeedidinonosasaururs).s). InsInsecectsts wewerere howhoweveever,r, impimportortantant diffdifferenerencesces inin the bodyypla bod plansns ofof insinsectsects modern in many respects by the dawn of the Cenozoic era and crustaceans, notably the presence of a second pair of (65 million years ago) in which we still live. antennae (antennules) and a nauplius larva in the latter. If TheTheorioriginginand relrelatiationsonshiphipssofof insinsectsectsare,,how are howeverever,,stilstilll HeHexaxapopodada is momostst clclososelelyy relrelatateded to CrCrusustataceacea,, ththenen a subject of debate and research (Figure 3). The earliest myriapods are related to ‘apterygotes’. known hexapod is a springtail, Rhyniella praecursor, from the Lower Devonian Rhynie Chert of Scotland dated at 396 million years (Ma) (Figure 4). Pterygote insects appear much later in the mid Carboniferous, cc. 330330Ma.Ma. InsectsInsects Insect Groups share featurefeaturesswithwithmyriapods myriapods (millipedes(millipedesand centipedes), centipedes), incincludludingtheingthepresenc presenceeofoftrachea tracheaeeandandMalMalpigpighiahianntubtubuleules.s. There is broad agreement about the composition of the TheTheyy alsalsoo share share feature featuress with with crustac crustaceanseans (crabs and major divisions (orders) of living Hexapoda. There is a shrshrimimpsps),), susuchch asas sisimimilalarirititieses inin ththeenenervrvouousssysystestemmananddththee vavaririabablele nunumbmberer of extextininctct orordedersrs sosomeme of whwhicichh are possession of compound eyes. A relationship with Crus- curcurrenrentlytlybeibeingng reireinternterprepretedted inin the liglightht ofof newnewstustudiediessandand tacea has been supported recently by the discovery of palaepalaeoentomoentomologiologicalcal discoveries. discoveries. Some entomoentomologislogiststs

Insecta (Insects)

Protura Entognatha Collembola Diplura Archaeognatha Monura Zygentoma Ectognatha Palaeodictyopteroidea Ephemeroptera Palaeoptera Dicondylia Protodonata Odonata Pterygota Plecoptera Embioptera Phasmatodea Orthoptera Grylloblattodea Protelytroptera Dermaptera Polyneoptera Miomoptera Blattodea Isoptera Protorozoptera Mantodea Caloneurodea Zoraptera Psocoptera Phthiraptera Paraneoptera

Thysanoptera Hemiptera Glosselytrodea Strepsiptera Coleoptera Rhapidioptera Megaloptera Neuroptera Hymenoptera Oligoneoptera Trichoptera Lepidoptera Diptera Siphonaptera Mecoptera

Figure 3 Provisional relationships among the major hehexapodxapod ggroupsroups (after Jarzembowski).Jarzembowski).

restrestricrictt the term insectinsect to pterygo pterygotestes and their closest closest using a special appendage called the spring (furca) on apterygote relatives and regard the remaining apterygotes abdabdomiominalnal segmen segmentt 4. There There is usuusuallallyy a ‘gl‘glue’ue’ tube as other groups of hexapods. The insect orders, with their (collophore) on segment 1 which is used for imbibing maimainn attattribributeutess and includ includeded grogroupsups,, are sumsummarmarizeizedd wawateter.r. CoCollllemembobolala araree amamonongg the most most imimpoportartantnt below. consumers in many soil ecosystems. .. Order Diplura (two-pronged bristletails): Dating from the Upper Carboniferous, diplurans are small or large, ‘Apterygotes’ narrow-bodied and mostly unpigmented, blind entognathous hexapods. There is a pair of cerci (‘tails’) on AptApterygerygoteotessareare priprimitmitiveivelylywingleglessss win insinsectsects..TheTheyyrangrangeeinin abdabdomiominalnalsegmen segmentt 1010(hence (hencethe common common namname)e) whiwhichch length from leslesss than 1 to 5050mm. Under 1% of all known may resemble antennae or forceps. Diplura are mainly hexapod species are apterygotes: they include Collembola, found in damp soil under logs or stonesstones.. Diplura, Protura, ‘Thysanura’ and Monura. .. Order Protura: There is no fossil record. proturans are very small, cryptic, mostly white entognathous hexa- .. Order Collembola (springtails): Found from the Lower DevDevonionianan onwards onwards,, these these small small or minute minute,, white white oror pods with no eyes or antennae. The front legs point pigmepigmentednted entognentognathousathoushexapohexapodsdsare calleddspring calle springtailstails forwforward.ard. They have no comcommonmon name but ProturProturaa because of the ability of many species to leap consider- meameansns ‘si‘singlnglee taitail’,l’, referringreferring to the simsimpleple pointed pointed ablableedisdistantancesces whewhenndisdisturbturbed.ed. The lealeappisis accompaccomplislishedhed

Insecta (Insects)

Palaeoptera ThTheseeseininsecsectsts cancannonottnonormrmalallyly fofoldld ththeieirrwiwingngssﬂaﬂattovoverer ththee body when at rest (due to lack of a structure at the wing base known as the third axillary sclerite). Some Palaeop- tera can, however, bend their wings back. Palaeopterous insinsectsectscompriprisese com two livlivinging ordordersers and sevseveraerallextiextinctnctones.s. one

.. Order Ephemeroptera (mayflies): Upper Carboniferous onwonwardards.s. DelDelicaicatete insinsectectss witwithh two or thrthreeee ‘ta‘tailsils’.’. Larvae with abdominal gills living in freshwater. Adult witwithh redreduceucedd hinhindwidwingsngs,, nonnon-fu-functinctionaonall (ve(vestistigiagial)l) mouthparts, and a subimago stage. Mayflies are not confined to the month of May, but many adults live fforor lelessss ththanan aadaday,y, hehencnceeththeieirrsciscienentitificfic nanameme (d(derieriveveddfrfromom the Greek ephemeros, short lived). .. Order Odonata (dragonflies and damselflies, sometimes FigFigure4ure4 RhyniellaRhyniellapraecurpraecursor sor reconstructed leapingleaping(after(after Jarzembowski). Length 1.5 mm. called dragondragonfliesflies collectivel collectively):y): Upper CarbonCarboniferouiferouss ononwawardrds.s. AdAdulultsts anandd lalarvrvaeae (n(nymymphphs)s) are acactitiveve abdomen. Proturans are found in soil but are uncom- prepredadatotorsrs.. LaLarvarvaee ususuauallllyy liliveve in frefreshshwawateterr wiwithth mon. tractracheaheall gilgillsls and exteextendandableble moumouthpathpartsrts for seiseizinzingg .. OrdOrderer ‘Thysan ‘Thysanuraura’’ (th(three-ree-taitailedled bribristlstletaietails)ls):: Thesese The preyprey.. AdultAdultss with two pairsrs pai of well-well-devdeveloelopedped winwingsgs and ectognathous hexapods have a carrot-shaped body with toothed jaws: they take insect prey on the wing, hunting shiny scales and two long, thread-like antennae plus by sisighght.t. ThThee adadulultsts mamayy be didististinctnctlyly papatttternerneded,, three long, segmented ‘tails’‘tails’,, hence the commoncommon name. associated with sexual dimorphism and well-developed ThThee orordederr is ofoftetenn spsplilitt inintoto twtwoo sesepapararatete orordedersrs vision. Dragonflies include the largest insects of all time Archaeognatha and Zygentoma, the former including in the extinct order Protodonata (Upper Carboniferous Petrobius found on the sea shore and the latter the to Triassic) some of which attained wingspwingspansans of 70 cm. dodomemestisticc sisilvlvererfisfishh anandd firfirebebrarat.t. ThThee exextitincnctt orordederr Monura (with only one ‘tail’) from the Upper Carbo- The Palaeoptera includes several extinct late Palaeozoic nifniferouerouss and PermPermianian is relrelateatedd to Archae Archaeognognathatha.a. orders collectivelcollectivelyy called the PalaePalaeodictyodictyopteroiopteroideadea (or Zygentoma are considered to be the closest relatives of ArcheoArcheoptera)ptera) which had beak-like beak-like mouthparts and are winwingedged insinsectsects (pteryg (pterygotesotes)) becaus becausee of similailar sim r jaw thought to have fed on plants. Some Palaeodictyopter- articulation and together form the Dicondylia. oidoideaea (Diaph (Diaphanoanopterpterodeodea)a) devdeveloelopedped a uniuniqueque winwing-g- folding mechanism.

Pterygotes Polyneoptera Primitively winged insects comprising 99% of all known These are the more primitive Neoptera with nine living ordordersers and seveseveralral extinc extinctiotions.ns. Both Both aduadultslts and larlarvaevae insect species. sizes range from very small to very large (ny(nymphmphs)s) are terrestr terrestrialial excexceptept in the ordorderer PlePlecopcopteratera (und(underer 11mmmm long to about 700mm wingspanwingspan (fossilsils)).)).(foss whwhereere the lalarvarvaee araree aqaquauatitic.c. ThThee lalarvarvaee araree ususuauallllyy TwTwoopapairirssofof wiwingngssarareeprpreseesentnt,,ononeeeaeachch ononthemimiddddlele the anandd ‘mi‘minianiaturturee aduadultslts’’ as in ParParaneaneopteoptera.ra. Mouthp Mouthpartsarts are hind thoracic segments, although the hind pair may be adapted for biting (cutting and chewing) a variety of food. reduced or lost, e.g. in certain parasitesparasites and undergroundunderground dwellers. Some fossil pterygotes had an additional pair of .. Order Blattodea (cockroaches): Upper Carboniferous ‘winglets’ on the front thoracic segment. Pterygotes have onwards. Body ﬂattened with large head shield (prono- two main divisions: exopterygotes and endopterygotes. tum) and leathery forewings (tegmina). .. OrderOrder DermapteraDermaptera (earwigs):(earwigs): Jurassic onwards. Abdo- men often often witwithh forcforcepseps.. ForForewiewingsngs redreduceduced to smallll sma Exopterygotes tegmina (like rove beetles). Hindwings, when present, TheThewinwingsgs devdeveloeloppextexternaernallyllyininthe juveni juvenilele insinsectect (la(larvarva oror larlargegeandfan andfan-sha-shapedped..SomSomeeearearwigwigfemfemalealessarearenotenoteddforfor nymph). Metamorphosis is incomplete (pauro- or hemi- their maternal care. The common name stems from the metabolous; Figure 2, left) and there is no pupal stage. fact that Dermaptera have been found occasionally in Exopterygotes comprise three groups: Palaeoptera, Poly- people’s ears (e.g. when camping or sleeping on straw neoptera and Paraneoptera; Polyneoptera and Paraneop- mattresmattresses)ses) associated with the insect’s cryptic beha- tera are the Neoptera.ra.Neopte viour.

Insecta (Insects)

.. Order Order Embioptera Embioptera (web-spinner (web-spinners):s): Permian Permian onwards.ds. onwar .. Order Order Phthiraptera (lice): Eocene onwaronwards.ds. WingWinglessless ForForeleelegsgs with with disdistintinctct swellillings swe ngs packed packed with with glands glands insects, parasitic on birds and mammals. Body flattened which are used to line tunnels with silk in which the whwhenen vivieweweded frfromom ababovovee wiwithth bibititingng or susuckckiningg insects live. mouthpmouthpartsarts in the divisdivisionsions ‘Malloph‘Mallophaga’aga’ and ‘Ano‘Ano-- .. OrderOrder Isoptera (termites):(termites): Lower CretaceousCretaceous onwards. plura’, respectively. SocSocialial insinsectectss with with reprod reproductiuctiveve forms forms (‘q(‘queeueens’ns’ and .. OrOrdederr Psococoptpterera Pso a (b(booookk anandd babarkrk lilice)ce):: PePermrmiaiann ‘kings’) and sterile soldiers and workers. They live in ononwawardrds.s. SmSmalalll ininsesectctss wiwithth a rorounundd heheadad,, lolongng family units (nests) in wood or earthen constructions, anteantennannae,e, bitbitinging moumouthpthpartsarts and winwingsgs oftoftenen helheldd sometimes in buildings. The reproductives can fly to roofwise (pitched at an angle) over the abdomen. They colonize new sites and shed their wings on landing. are mainly scavengers. .. Order Mantodea (praying mantises): mantises): Cretaceous on- .. Order Thysanoptera (thrips): Permian onwards. Small, wards. Predators with distinctive spiny front legs used slendeslenderr insectinsectss with asymmetric mouthpartmouthpartss adapteadaptedd for catching insect prey. The name mantis is derived for sucking plants. Wings, when present, narrow with from the Greek for holy person, and the common name redureducedced venvenatiationon and a haihairyry frifringenge resembl resemblinging tintinyy also reflects the resemblanresemblancece to the act of praying when featfeathershers..(Th(Theelatlatiniinizedzed namnameeofof the orderer ord meameansns ‘fr‘fringinge-e- awaiting prey. wings’.) .. OrderOrder Orthoptera (crickets, grasshoppers, katydidskatydids and locustlocusts):s): Upper CarboniferCarboniferousous onwards. onwards. Insects with PaPararaneneopopteterourouss ininsesectscts alalsoso ininclclududee ththee titinyny lilivivingng hind legs usually adapted for jumping and pronotum ordorderer Zorapt Zorapteraera,, and somsomee extinct extinct PalPalaeoaeozoizoicc ‘pr‘proto-oto- extended down the side of the body. Males of many rthopterans’. species produce distinctive calls (songs) by rasping the forewings or forewings/hind legs together. .. Order Phasmatodea (stick insects): Permian onwards. Endopterygotes (Oligoneoptera, Endopterygota, Plant-feeding insects with a remarkable resemblance to Holometabola) sticks and leaves. Reproduction without males (parthe- These are insects in which the wings develop internally nogenesis) occurs in some species. (hence EndopterygEndopterygota)ota) and metamometamorphosirphosiss is complcompleteete .. OrderOrder Plecoptera (stoneflies): Permian onwards. LarvLarvaeae (holometabolous, FigFigureure 22, rigright)ht).. TheTheyy compriprise com se 80% (ny(nymphmphs)s)usuallallyylivliveeinin usu frefreshwshwateraterandandhaveenono hav gilgillslsand of known insect species with one extinct and eleven livinlivingg only two long ‘tails’. The adults often have distinctive orordedersrs,, alalththououghgh most most of ththee bibiododiviverersisityty is in fofourur veiveinsns reseresemblmblingaingapairrofoflad pai ladderderssinintheitheirrwinwings,gs,andmayandmay ordersorders(Coleo(Coleoptera,ptera,DipteDiptera,ra, HymenHymenoptera,optera,LepidoLepidoptera):ptera): be found among waterside stones, from which they get their common name. .. Order Coleoptera (beetles; Permian onwards): These minminuteutetoto larlargege insinsectectssnormnormallallyyhavhaveebitbitingmouthpingmouthpartarts.s. The front pair of wings are modified into rigid wing The polpolyneyneopteopterourouss insinsectsects alsalsoo includ includee the folfollowlowinging cases called elytra. The elytra usually meet edge to edge orders: GryllGrylloblatoblattodea,todea, ProtelProtelytropteytroptera,ra, CalonCaloneurodeaeurodea,, in a straight line when at rest and partly or wholly Miomoptera and ‘Protorthoptera’ of which the first is still cover the hindwings and abdomen. 40% of all insects livinlivingg but rare and the others are all extinct. anandd 3030%% of alalll ananimimalalss are bebeetetleles;s; ththee nunumbmberer of of beetle species is six (or more) times greater than that of Paraneoptera vertvertebraebratestes..TheThe sinsinglegle mosmosttimpimportortantant factfactoror concontritributbut-- ing to the success of the Coleoptera is the evolution of These are characterized mainly by reductions in internal the elytra, protecting the body and facilitating life in organs and foot segmentation. There are five living orders enclosed spaces and cryptic habitats. Beetles are mainly and some extinct groups. terrestrial, but some are aquatic. .. Order Hemiptera (true bugs): Permian onwards. The .. Order DipDipteratera(tru(trueeoror twotwo-wi-wingengeddflieflies,s, incincludludinginggnagnats,ts, dominant order of exopterygote insects with piercing midges, mosquitoes and bluebottles; Triassic onwards): momoututhphparartsts adadapaptedted foforr susuckickingng.. In ththee susuboborderderr These minute to moderately large insects have only the HomoHomopteraptera (including (including leafhleafhoppers,oppers, cicadas, cicadas, aphids,s, aphid frofrontnt papairir of wiwingngss ususuauallllyy prpreseesentnt,, ththee hihindndwiwingngss scale insects and whitefly) the forewings are usually of havhavinging becbecomeome altalteredered to club-lb-like clu ike balbalancancee organs organs eveevenn consissisten con tencycy wherea whereass in Hetero Heteropterpteraa (true (true bugs)s) bug (halteres). Wings are translucent with few cells, absent ththeyey may may hahaveve a sosoftft ououteterr papartrt,, e.e.g.g. shshieieldld bubugsgs.. in parasitic forms. Mouthparts are adapted for sucking Homopterans feed only on plant juices, whereas some or mopping up liquids, e.g. houseflies and for ‘biting’ hetheteroperopterateransns alsalsoosucsuckkblobloodod andandincincludludeeaquaquatiaticcforformsms (piercing and sucking), e.g. mosquitoes. Some species (e.g. pond skaters, water boatmen). Bugs can transmit transmit virulent diseases and many mimic bees and plant and occasionall occasionallyy human diseases (Chaga’s dis- waswaspsps for proprotecttectionion (see below)below).. LarLarvaevae laclackk true ease). leglegss and are usuallally usu y magmaggotgot-li-like.ke. PupPupaeae somsometietimesmes

Insecta (Insects)

dedevevelolopp in a toutoughgh skskinin (p(pupuparariuium)m).. DiDiptptereraa araree .. OrOrderder NeuropNeuropteratera (lacew(lacewingsings and antlions; antlions; PermiPermianan oftoftenen associ associateatedd witwithh moist moist sitsituatiuationsons and decayin decayingg onwards): These insects, which may be small or large, material. usuusualallyly hahaveve twtwoo sisimimilalarr papairirss of wiwingngss whwhicichh araree .. OrOrdederr Hyme Hymenonoptptereraa (s(sawawfliflieses,, wawaspsps,s, hohornrnetets,s, larlargege and coveredcovered witwithh a comcompleplexx networ networkk of veiveinsns ichneumons, ants and bees; Triassic onwards): These and held held rooroofwifwisese when when not flyiflying.ng. NeuNeuropropteratera are miminunutete to lalargerge ininsecsectsts usuusualallyly hahaveve twtwoo papairirss of of predators and larvae have distinctive sucking jaws used tratranslnsluceucentnt wings wings of which which the front pair pair is larlargerger.. to catch other insects, e.g. ants and aphids. Larvae are The wings are coupled by a row of minute hooks on the terrestrial or aquatic. Adult antlions resemble dragon- front edge of the hindwing.hindwing. The wing venation consisconsiststs flies and mantisflies resemble praying mantises. o f of lalargrgee cecelllls,s, or mamayy be grgreaeatltlyy rereduduceced.d. BiBititingng .. OrdOrderer Megalo Megaloptepterara (al(alderder flies): flies): TheThesese medmediumium-si-sizeze momoututhphparartsts may may be acaccocompmpananieiedd by a totongngueue for or large insects are sometimes included in Neuroptera. lalappppiningg up liliququidids,s, as in bees, bees, to cocollllecectt nectatar nec r for Larvae have biting mouthparts and are aquatic. making honey as larval food. A well-developed egg- .. OrdOrderer RapRaphidhidiopiopteratera (sn(snakeake flieflies):s): TheThesese medium medium-- laying organ (ovipositor) is usually found in females, sizsizee insinsectsects are sometietimes som mes includ includeded in NeuNeuropropteratera.. sometimes used as a sting. Larvae are terrestrial, with Larvae have biting mouthparts and are terrestrial. or without legs. Wasps, hornets, ichneumons and bees .. OrOrdederr SiSiphphononapapteterara (fl(fleaeas;s; CrCretetacaceoueouss ononwawardrds)s):: have a very narrow ‘waist’ which is absent in sawflies. Fleas are small, wingless insects compressed sideways The ovipositor in sawflies is used for cutting slits in (unl(unlikeike liclice)e) witwithh bloblood-od-sucsuckinkingg moumouthpthpartarts.s. TheTheyy plplanants,ts, hehencncee ththee cocommmmonon nanameme.. IcIchnhneueumomonsns anandd are parasites of birds and mammals. manmanyywaswaspspsare parasiasitictic par ononotherrinsinsectectssand othe andimpimportaortantnt .. OrderOrder StrepsipteraStrepsiptera (stylopids;(stylopids; Eocene onwardonwards):s): Small in ‘biological control’. Some bees are also parasitic, e.g. parasites with extreme sexual dimorphism. Males are cucuckckoooo bebeeses.. Waspsps, Wa s, anantsts anandd bebeeses hahaveve evolvlveded evo freefree-li-livinving,g, and havhavee functictiona fun onall hinhindwidwingsngs with with the euseusociocialialityty indepe independendentlntlyy of the termiteites term s and havee hav foreforewinwingsgs modifie modifiedd as haltere halteress (unliklike (un e in DipDipteratera).). reproductives and workers inhabiting earth or paper The females are grub-like and generally stay in the host. nesnests.ts. The colcolonionieses are domina dominatedted by ‘qu‘queeneens’.s’. Ant .. Order TriTrichochoptepterara (caddi (caddisflisflies,es, sedsedgege fliefliess or rairailsls of of rereprprododucuctitivevess cacann shsheded ththeieirr wiwingngs,s, lilikeke tetermrmititeses,, fishfisherermemen;n; PePermrmiaiann ononwawardsrds):): ThTheseese araree smsmalalll oror altalthouhoughgh worker workerss laclackk wings, wings, unlike unlike wasp wasp and bee medmediumium-si-size,ze, motmoth-lh-likeike insinsectsects witwithh lonlongg antantennennae,ae, workers which are noted insect predators and pollina- lalargrgee cocompmpououndnd eyeyeses anandd wwiningsgs hehelldd roroofofwwisisee tors of flowers, respectively. There are many solitary whwhenen nonott flyflyining.g. Adulults Ad ts araree reareadidilyly didististingnguiuishsheded wasps and bees, unlike ants. from moths by being covered in small hairs and few (if .. O Orderrder Lepido Lepidopterpteraa (moths (moths and butterfl butterfliesies,, Jurassi Jurassicc anyany)) scascalesles,, havhavinging redureducedced moumouthpthpartsarts,, and beibeingng onwards): These insects, which may be small or large, founfoundd neanearr water water whewherere the larvae live.live. The larvalarvaee usually have two pairs of wings which, together with have biting mouthparts and often live in fixed shelters ththee bobodydy,, araree more more or lelessss coverered cov ed wiwithth titinyny scaleless sca or poportartablblee cacasesses whicich wh h ththeyey conconststruructct of vavaririououss (flatten(flatteneded hairs).hairs). Most adult LepidopteraLepidoptera have tubularrtubula materials. suckinsuckingg mouthpartsmouthparts (proboscises)(proboscises) for feeding on juices lilikeke nenectctarar (a(altlthohougughh sosomeme hahaveve prprimimititivivee bibititingng moumouthpthpartsarts)) witwithh the probos probosciscis coiled coiled liklikee a watchch wat There is one extinct order of Oligoneoptera: the Glossely- spring when not in use. Larvae (caterpillars) have biting trodea (Permian to Jurassic). moumouthpthpartsarts mostly mostly for chewchewinging plants plants and includ includee pests of crops and garden plants. Exceptions include the clothes moth, which feeds on animal material such as wool. wool. Some Some caterpi caterpillallarsrs spispinn a protect protectiveive cocoon cocoon General Biology bebefoforere pupupapatitingng,,asas ininthesilkmoththesilkmoth,,ththeeththrereadadssofofwhicichh wh are used to weave a quality fabric. Day-flying Lepidop- Exoskeleton and growth tera include some of the most colourful insects, the wing patterns being formed by natural pigment and irides- The insect exoskeexoskeletletonon (cu(cuticticle)le) is madmadee of chitin chitin and cence, the latter provided by the microscopic structure sclerotin, the latter forming the hard outer layer, as well as of the scales. proteiproteinn and a waxy externexternalalcoating. coating. Insect larlarvaevae grow by .. OrdeOrderr Mecopt Mecopteraera (scorpirpionfl (sco onfliesies;; PerPermiamiann onwonwardsards):): sheddisheddingng their exoskeletoexoskeletonn periodperiodicallically,y, e.g. nymphs of aa Scorpionflies are small or medium-size insects in which hemhemimeimetabotaboloulouss grasgrasshoshoppepperr moumoultlt five to eigeightht timeses tim the head is typically extended downwards to form a ((Figure 2, left). Ametabolous insects (without metamor- bebeakak wiwithth ththeemomoututhphparartsts atat ththe ee endnd..ThTheetitippooff ththeemamalele phosis) continue to moult into adult life, altogether as abdomen is often curved up and swollen, resembling a much as 50 times in the silverfish. The growth period of scoscorpirpion’on’ss stisting.ng. Some Some speciecies spe s hang hang from from plants plants byby ininsecsectsts tetendndss to be fasteter fas r in hohott clclimimateates.s. A trotropipicalcal the forelegs. Larvae are terrestrial. bubutttterflerflyy may may develelop dev op frofromm egeggg to adadulultt in 3 weweekeks,s,

Insecta (Insects)

whereas in temperate regions there are usually only one to Insects also have touch sensors, heat and temperature three generations per annum. detectors.

Internal organs ThTheeguguttisis a tutubebe (w(witithhpopoucuchehes)s)extenendidingng ext frommththeemo fro moututhh Survival to the anus. Excretion is done mainly via the Malpighian Many small insects depend on sheer fecundity to outstrip tubules, which are blind, narrow tubes attached to the gut predation. Larger insects with smaller populations may cavitiesand producing (the haemocoel) uric acid. Bloodand there bathes are thefew organs blood inve ssels.large hidhideeoror disdisplaplayyproprotecttectiveive camcamouflouflageage,,e.ge.g..lealeaffinsinsectects.s. The blblacackk anandd yeyellllowow or reredd strstripipeses of wawaspspss araree wawarnirningng Air isis supsuppliplieded to the livlivinging tistissuessues(anddnot (an not theblood) blood) byby aa colours that the insects can sting and birds soon learn to network of chitinous tubes (tracheae and tracheoles) from avoid them. To discourage predators, many insects have a about 10 pairs of openings (spiracles) on the sides of the nasty taste, e.g. burnet moths, or irritant hairs, e.g. the body. Many aquatic larvae get their oxygen by simple brobrown-wn-taitaill motmothh catcaterpierpillallar.r. SomSomee defence defenceleslesss specspeciesies diffusion. mimmimicic waswasppcolcoloraoratiotionnforfor protprotectiection,on, e.ge.g..thethewasp wasp beetle.e.beetl Palatable species can resemble unpalatable ones, e.g. in Senses butterflies the viceroy resembles the monarch. Some insect lalarvrvaeae arareeprprototectecteded byby bebeininggsusurrorrounundededdinin fofoodod,,e.e.g.g. gagallll-- Sight forming and leaf-mining insects and dung-flies. The compound eyes are made up of a number of similar liglight-sht-sensiensitivtivee units units (ommat (ommatidiidia).a). Each Each unit unit has a lenss len givgivingingthetheeyeeyeaafacefacetedtedappappearearanceance..DraDragongonfliefliesshavhaveegoogoodd visvisionionwitwithhupup toto 3030 000000ommommatiatidiadia..InseInsectsctsalsalsoohavhaveesinsinglegle Further Reading eyes (ocelli). Carpenter FM (1992) Superclass Hexapoda. Treatise on Invertebrate Smell Paleontology, ParPartt R, ArthropoArthropodada 4, 3 & 4. Lawrencence:Lawr e: KanKansassas University Press. ThThisis sesensnsee is lolocacatetedd in ththee anantetennnnaeae.. ThThee brbrananchcheded Chinery M (1993) InsecInsectsts of BritaBritainin and NortNorthernhern Europe, 3rd edn. antennae of some male moths can detect female scent over London: HarperCollins. several miles, e.g. in the emperor moth. Commonwealth Scientific and Industrial Research Organisation (1991) The Insects of Australia, 2nd edn. vols 1 and 2. Carlton: Melbourne Sound and hearing University Press. Daly HV, Doyen JT and Purcell AH III (1998) Introduction to Insect Crickets, cicadas and other insects produce songs which Biology and Diversity, 2nd edn. Oxford: Oxford University Press. they hear with ears (tympanal(tympanal organs) on various parts of Jarzembowski EA and Ross AJ (1996) Insect originatioriginationon and extinction the body. Night-flying moths can hear bat calls and take in the Phanerozoic. Bioti Bioticc RecoveRecoveryry from Mass ExtinExtinctioctionn EventEventss,, evasive action. Geological Society, Special Publication, no. 102, pp. 65–78. London. JolivJolivetet P (1998)) (1998 Interrel Interrelatioationshipnshipss BetweeBetweenn InsecInsectsts and PlantPlantss. Boca Taste Raton, FL: CRC Press.

InseInsectscts can taste taste witwithh thetheirir feefeett (ta(tarsirsi)) as well as theirir the Parkervol. 2. SP New (ed.) York: (1982) McGraw-Hill. Synopsis and Classiﬁcation of Living Organisms,, mouths, e.g. the red admiral butterﬂy can detect even very WilsWilsonon EO (1971) The InsecInsectt SocieSocietiesties. Cambridge, Cambridge, MA: Belknap/ Belknap/ weak sugar solution with its forefeet. Harvard University Press.