Insects (frae Laitin insectum, a calque o Greek ἔντομον [éntomon], "cut intae sections") are a cless (Insecta) o hexapod invertebrates within the arthropod phylum that hae a chitinous exoskeleton, a three-pairt bouk (heid, thorax an abdomen), three pairs o jyntit legs, compoond een an ane pair o antennae. Thay are the maist diverse group o ainimals on the planet, includin mair nor a million descrived species an representin mair nor hauf o aw kent leevin organisms.[2][3] The nummer o extant species is estimatit at atween sax an ten million,[2][4][5] an potentially represent ower 90% o the differin ainimal life forms on Yird.[6] Insects mey be foond in nearly aw environs, awtho anerly a smaw nummer o species dwall in the oceans, a habitat dominatit bi anither arthropod group, crustaceans.
The life cycles o insects vary but maist hatch frae eggs. Insect growthe is constrained bi the inelastic exoskeleton an development involves a series o mouts. The immatur stages can differ frae the adults in structur, haibit an habitat, an can include a passive pupal stage in thae groups that unnergae 4-stage metamorphosis (see holometabolism). Insects that unnergae 3-stage metamorphosis lack a pupal stage an adults develop throu a series o nymphal stages.[7] The heicher level relationship o the Hexapoda is unclear. Fossilised insects o enormous size hae been foond frae the Paleozoic Era, includin giant draigonflees wi weengspans o 55 tae 70 cm (22–28 in). The maist diverse insect groups appear tae hae coevolved wi flouerin plants.
Adult insects teepically muive aboot bi walkin, fleein or whiles soummin (see § Locomotion ablo). As it allaes for rapid yet stable muivement, mony insects adopt a tripedal gait in which thay walk wi thair legs titchin the grund in alternatin triangles. Insects are the anerly invertebrates tae hae evolved flicht. Mony insects spend at least pairt o thair leeves unner watter, wi larval adaptations that include gills, an some adult insects are aquatic an hae adaptations for soummin. Some species, such as watter striders, are capable o walkin on the surface o watter. Insects are maistly solitar, but some, such as certain bees, eemocks an termites, are social an leeve in lairge, well-organised colonies. Some insects, such as earwigs, shaw maternal care, guardin thair eggs an young. Insects can communicate wi each ither in a variety o weys. Male mochs can sense the pheromones o female mochs ower great distances. Ither species communicate wi soonds: cheepers stridulate, or rub thair weengs thegither, tae attract a mate an repel ither males. Lampyridae in the clock order communicate wi licht.
Humans regaird certain insects as pests, an attempt tae control them uisin insecticides an a host o ither techniques. Some insects damage crops bi feedin on sap, leafs or fruits. A few parasitic species are pathogenic. Some insects perform complex ecological roles; blaw-flees, for example, help consume carrion but an aa spreid diseases. Insect pollinators are necessar tae the life cycle o mony flouerin plant species on which maist organisms, includin humans, are at least pairtly dependent; withoot them, the terrestrial portion o the biosphere (includin humans) wad be devastatit.[8] Mony ither insects are conseedert ecologically benefeecial as predators an a few provide direct economic benefit. Soiewirms an bees hae been uised extensively bi humans for the production o soie an hinnie, respectively. In some culturs, fowk eat the larvae or adults o certain insects.
The wird "insect" comes frae the Laitin wird insectum, meanin "wi a notched or dividit bouk", or leeterally "cut intae", frae the neuter seengular perfect passive pairteeciple o [insectare] error: {{lang}}: text haes italic markup (help), "tae cut intae, tae cut up", frae in- "intae" an secare "tae cut";[9] acause insects appear "cut intae" three sections. Pliny the Elder introduced the Laitin designation as a lend-translation o the Greek wird ἔντομος (éntomos) or "insect" (as in entomology), which wis Aristotle's term for this cless o life, an aa in reference tae thair "notched" bouks.
Tradeetional morphology-based or appearance-based systematics hae uisually gien the Hexapoda the rank o supercless,[10]:180 an identifee'd fower groups within it: insects (Ectognatha), springtails (Collembola), Protura, an Diplura, the latter three bein grouped thegither as the Entognatha on the basis o internalised mooth pairts. Supraordinal relationships hae unnergane numerous chynges wi the advent o methods based on evolutionary history an genetic data.
Insect bouks are dividit up intae three main pairts, the heid, thorax, an abdomen. The heid is enclosed in a haurd, hivily sclerotised, unsegmentit, exoskeletal heid capsule, or epicranium, which conteens maist o the sensin organs, includin the antennae, ocellus or een, an the moothpairts. The thorax is a tagma componed o three sections, the prothorax, mesothorax an the metathorax. The anterior segment, closest tae the heid, is the prothorax, wi the major featurs bein the first pair o legs an the pronotum. The middle segment is the mesothorax, wi the major featurs bein the seicont pair o legs an the anterior weengs. The third an maist posterior segment, abuttin the abdomen, is the metathorax, which featurs the third pair o legs an the posterior wings. The abdomen is the lairgest tagma o the insect, which teepically conseests o 11–12 segments an is less strangly sclerotised nor the heid or thorax. Each segment o the abdomen is representit bi a sclerotised tergum an sternum.
The insect ooter skelet, the cuticle, is made up o twa layers: the epicuticle, which is a thin an wauxy watter reseestant ooter layer an conteens na chitin, an a lawer layer cried the procuticle. The procuticle is chitinous an much thicker nor the epicuticle an haes twa layers: an ooter layer kent as the exocuticle an an inner layer kent as the endocuticle. The teuch an flexible endocuticle is biggit frae numerous layers o feebrous chitin an proteins, criss-crossin each ither, while the exocuticle is rigid an haurdened.[10]:22–24
he nervous system o an insect can be dividit intae a harn an a ventral nerve cord. The heid capsule is made up o sax fused segments, each wi either a pair o ganglia, or a cluster o nerve cells ootside o the harn. At least a few insects hae nociceptors, cells that detect an transmit signals responsible for the sensation o pyne.[11] Insects are capable o learnin.[12]
An insect uises its digeestive seestem tae extract nutrients an ither substances frae the fuid it consumes.[13] Maist o this fuid is ingeestit in the form o macromolecules an ither complex substances lik proteins, polysaccharides, fats an nucleic acids. The main structur o an insect's digeestive seestem is a lang enclosed tube cried the alimentary canal, which runs langwyse throu the bouk. The alimentary canal directs fuid unidirectionally frae the mooth tae the anus.
The reproductive seestem o female insects conseest o a pair o ovaries, accessory glands, ane or mair spermathecae, an ducts connectin thir pairts. The ovaries are made up o a nummer o egg tubes, cried ovarioles, which vary in size an nummer bi species. The nummer o eggs that the insect is able tae mak vary bi the nummer o ovarioles wi the rate that eggs can develop bein an aa influenced bi ovariole design. For males, the reproductive seestem is the testis, suspendit in the bouk cavity bi tracheae an the fat bouk.
Insect respiration is accomplished withoot buffs. Insteid, the insect respiratory seestem uises a seestem o internal tubes an sacs throu which gases either diffuise or are actively pumped, deliverin oxygen directly tae tishies that need it via thair trachea (element 8 in nummered diagram). Syne oxygen is deleevered directly, the circulatory seestem is nae uised tae cairy oxygen, an is tharefore greatly reduced. The insect circulatory seestem haes na veins or arteries, an insteid conseests o little mair nor a single, perforatit dorsal tube which pulses peristaltically. Taewart the thorax, the dorsal tube (element 14) divides intae chaumers an acts lik the insect's hert. The opposite end o the dorsal tube is lik the aorta o the insect circulatin the hemolymph, arthropods' fluid analog o bluid, inside the bouk cavity.[10]:61–65[14] Air is taken in throu openins on the sides o the abdomen cried spiracles.
Mony insects possess very sensitive an, or specialised organs o perception. Some insects such as bees can perceive ultraviolet wavelenths, or detect polarised licht, while the antennae o male mochs can detect the pheromones o female mochs ower distances o mony kilometres.[15] Some insects display a rudimentar sense o nummers,[16] such as the solitar wasps that prey upon a single species. The mither wasp lays her eggs in individual cells an provides each egg wi a nummer o live caterpillars on which the young feed when hatched.
A few insects, such as members o the faimilies Poduridae an Onychiuridae (Collembola), Mycetophilidae (Diptera) an the clock faimilies Lampyridae, Phengodidae, Elateridae an Staphylinidae are bioluminescent. The maist faimiliar group are the fireflees, clocks o the faimily Lampyridae. Some species are able tae control this licht generation tae produce flashes. The function varies wi some species uisin them tae attract mates, while ithers uise them tae lure prey. Maist insects, except some species o cove cheepers, are able tae perceive licht an daurk.
Insects war the earliest organisms tae produce an sense soonds. Insects mak soonds maistly bi mechanical action o appendages. In gresslowpers an cheepers, this is achieved bi stridulation. Cicadas mak the loodest soonds amang the insects bi producin an amplifeein soonds wi special modifications tae thair bouk an musculature. The African cicada Brevisana brevis haes been meisurt at 106.7 decibels at a distance o 50 cm (20 in).[17] Some insects, such as the Helicoverpa zea mochs, hawk mochs an Hedylid butterflees, can hear ultrasoond an tak evasive action when thay sense that thay hae been detectit bi baukies.[18][19]
Social insects, such as termites, eemocks an mony bees an wasps, are the maist familiar species o eusocial ainimal.[20] Thay leeve thegither in lairge well-organised colonies that mey be sae tichtly integratit an genetically seemilar that the colonies o some species are whiles conseedert superorganisms. It is whiles argied that the various species o hinnie bee are the anerly invertebrates (an indeed ane o the few non-human groups) tae hae evolved a seestem o abstract seembolic communication whaur a behaviour is uised tae represent an convey speceefic information aboot something in the environment.
Insects are the anerly group o invertebrates tae hae developed flicht. Insect flicht haes been a topic o great interest in aerodynamics due pairtly tae the inabeelity o steady-state theories tae expleen the lift generatit bi the tottie weengs o insects. But insect weengs are in motion, wi flappin an vibrations, resultin in churnin an eddies, an the misconception that pheesics says "bumbees canna flee" perseestit ootthrou maist o the twintiet century. Unlik birds, mony smaa insects are swept alang bi the prevailin winds[21] awtho mony o the lairger insects are kent tae mak migrations.
Mony adult insects uise sax legs for walkin an hae adoptit a tripedal gait. The tripedal gait allaes for fest walkin while ayeweys haein a stable stance an haes been studied extensively in cockroaches.
A lairge nummer o insects leeve either pairt or the whole o thair leeves unnerwatter. In mony o the mair primitive orders o insect, the immatur stages are spent in an aquatic environment. Some groups o insects, lik certain watter clocks, hae aquatic adults as well.[22]
Insects (frae Laitin insectum, a calque o Greek ἔντομον [éntomon], "cut intae sections") are a cless (Insecta) o hexapod invertebrates within the arthropod phylum that hae a chitinous exoskeleton, a three-pairt bouk (heid, thorax an abdomen), three pairs o jyntit legs, compoond een an ane pair o antennae. Thay are the maist diverse group o ainimals on the planet, includin mair nor a million descrived species an representin mair nor hauf o aw kent leevin organisms. The nummer o extant species is estimatit at atween sax an ten million, an potentially represent ower 90% o the differin ainimal life forms on Yird. Insects mey be foond in nearly aw environs, awtho anerly a smaw nummer o species dwall in the oceans, a habitat dominatit bi anither arthropod group, crustaceans.
The life cycles o insects vary but maist hatch frae eggs. Insect growthe is constrained bi the inelastic exoskeleton an development involves a series o mouts. The immatur stages can differ frae the adults in structur, haibit an habitat, an can include a passive pupal stage in thae groups that unnergae 4-stage metamorphosis (see holometabolism). Insects that unnergae 3-stage metamorphosis lack a pupal stage an adults develop throu a series o nymphal stages. The heicher level relationship o the Hexapoda is unclear. Fossilised insects o enormous size hae been foond frae the Paleozoic Era, includin giant draigonflees wi weengspans o 55 tae 70 cm (22–28 in). The maist diverse insect groups appear tae hae coevolved wi flouerin plants.
Adult insects teepically muive aboot bi walkin, fleein or whiles soummin (see ablo). As it allaes for rapid yet stable muivement, mony insects adopt a tripedal gait in which thay walk wi thair legs titchin the grund in alternatin triangles. Insects are the anerly invertebrates tae hae evolved flicht. Mony insects spend at least pairt o thair leeves unner watter, wi larval adaptations that include gills, an some adult insects are aquatic an hae adaptations for soummin. Some species, such as watter striders, are capable o walkin on the surface o watter. Insects are maistly solitar, but some, such as certain bees, eemocks an termites, are social an leeve in lairge, well-organised colonies. Some insects, such as earwigs, shaw maternal care, guardin thair eggs an young. Insects can communicate wi each ither in a variety o weys. Male mochs can sense the pheromones o female mochs ower great distances. Ither species communicate wi soonds: cheepers stridulate, or rub thair weengs thegither, tae attract a mate an repel ither males. Lampyridae in the clock order communicate wi licht.
Humans regaird certain insects as pests, an attempt tae control them uisin insecticides an a host o ither techniques. Some insects damage crops bi feedin on sap, leafs or fruits. A few parasitic species are pathogenic. Some insects perform complex ecological roles; blaw-flees, for example, help consume carrion but an aa spreid diseases. Insect pollinators are necessar tae the life cycle o mony flouerin plant species on which maist organisms, includin humans, are at least pairtly dependent; withoot them, the terrestrial portion o the biosphere (includin humans) wad be devastatit. Mony ither insects are conseedert ecologically benefeecial as predators an a few provide direct economic benefit. Soiewirms an bees hae been uised extensively bi humans for the production o soie an hinnie, respectively. In some culturs, fowk eat the larvae or adults o certain insects.
