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Insects (Class Insecta) are arthropods, having a hard exoskeleton, a three-part body (head, thorax, and abdomen), three pairs of jointed legs, compound eyes, and two antennae. They are the most diverse group of animals on the planet and include approximately 2,200 species of praying mantis, 5,000 dragonfly, 20,000 grasshopper, 82,000 true bug, 120,000 fly, 110,000 bee, wasp, ant and sawfly, 170,000 butterfly and moth, and 360,000 beetle species described to date. The number of extant species is estimated at between six and ten million, with over a million species already described. Insects represent more than half of all known living organisms and potentially represent over 90% of the differing life forms on Earth. Insects may be found in nearly all environments, although only a small number of species occur in the oceans, a habitat dominated by another arthropod group, the crustaceans.
Adult modern insects range in size from a 0.139 mm (0.00547 in) fairyfly (Dicopomorpha echmepterygis) to a 56.7-centimetre (22.3 in) long stick insect (Phobaeticus chani). The heaviest documented present-day insect was 70 g (2½ oz) Giant Weta, though the Goliath beetles Goliathus goliatus, Goliathus regius and Cerambycid beetles such as Titanus giganteus hold the title for some of the largest species in general.
The largest known extinct insect is a kind of dragonfly, Meganeura.
Arachnids are a class (Arachnida) of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term arachnid is from the Greek word άράχνη or arachne, meaning spider, and also referring to the mythological figure Arachne.
Most arachnids are terrestrial. However, some inhabit freshwater enviroments and, with the exception of the pelagic zone, marine environments as well. They comprise over 100,000 named species, including spiders, scorpions, harvestmen, ticks, and mites.
Centipedes (from Latin prefix centi-, «hundred», and Latin pes,pedis, «foot») are arthropods belonging to the class Chilopoda and the Subphylum Myriapoda. They are elongated metameric animals with one pair of legs per body segment. A key trait uniting this group is a pair of venom claws or forcipules formed from a modified first appendage. This also means that centipedes are an exclusively predatory taxon, which is uncommon.
Centipedes normally have a drab coloration combining shades of brown and red. Cavernicolous and subterranean species may lack pigmentation and many tropical Scolopendromorphs have bright aposematic colors. Size can range from a few millimeters in the smaller Lithobiomorphs and Geophilomorphs to about 30 cm in the largest Scolopendromorphs. Centipedes can be found in a wide variety of environments.
Worldwide there are estimated to be 8,000 species. Currently there are about 3,000 described species. Geographically, centipedes have a wide range, which reaches beyond the Arctic Circle. Centipedes are found in an array of terrestrial habitats from tropical rainforests to deserts. Within these habitats centipedes require a moist micro-habitat due to their rapid rates of water loss. Accordingly, they are found in soil and leaf litter, under stones and deadwood, and inside logs. In addition, centipedes are one of the largest terrestrial invertebrate predators and often they contribute a significant proportion to invertebrate predatory biomass in terrestrial ecosystems.
Hemimetabolism or hemimetaboly, also called incomplete metamorphosis, is a term used to describe the mode of development of certain insects that includes three distinct stages: the egg, nymph, and the adult stage, or imago. These groups go through gradual changes; there is no pupal stage. The nymph often resemble the adult somewhat, as they have compound eyes, developed legs and wing stubs visible on the outside.
Holometabolism, also called complete metamorphism, is a term applied to insect groups to describe the specific kind of insect development which includes four life stages — as an embryo, a larva, a pupa and an imago. For example, in the life cycle of a butterfly, the embryo grows within the egg, hatching into the larval stage caterpillar, before entering the pupal stage within its chrysalis and finally emerging as an adult butterfly imago.
A butterfly is an insect of the order Lepidoptera. Like all Lepidoptera, butterflies are notable for their unusual life cycle with a larval caterpillar stage, an inactive pupal stage, and a spectacular metamorphosis into a familiar and colourful winged adult form. Most species are day-flying so they regularly attract attention. The diverse patterns formed by their brightly coloured wings and their erratic yet graceful flight have made butterfly watching a hobby.
Butterflies comprise the true butterflies (superfamily Papilionoidea), the skippers (superfamily Hesperioidea) and the moth-butterflies (superfamily Hedyloidea). Butterflies exhibit polymorphism, mimicry and aposematism. Some migrate over long distances. Some butterflies have evolved symbiotic and parasitic relationships with social insects such as ants. Butterflies are important economically as agents of pollination. In addition, a few species are pests, because they can damage domestic crops and trees in their larval stage.
Mantodea or mantises is an order of insects which contains approximately 2,200 species in 9 families worldwide in temperate and tropical habitats. Most of the species are in the family Mantidae. Historically, the term «mantid» was used to refer to any member of the order because for most of the past century, only one family was recognized within the order; technically, however, the term only refers to this one family, meaning the species in the other eight recently-established families are not mantids, by definition (i.e., they are empusids, or hymenopodids, etc.), and the term «mantises» should be used when referring to the entire order. A colloquial name for the order is «praying mantises», because of the typical «prayer-like» stance, although the term is often mis-spelled as «preying mantis» since mantises are notoriously predatory. The word mantis is Greek for «prophet» or «fortune teller». In Europe, the name «praying mantis» refers to only a single species, Mantis religiosa. The closest relatives of mantises are the orders Isoptera (termites) and Blattodea (cockroaches), and these three groups together are sometimes ranked as an order rather than a superorder. They are sometimes confused with phasmids (stick/leaf insects) and other elongated insects such as grasshoppers and crickets.
Flea is the common name for insects of the order Siphonaptera which are wingless insects whose mouthparts are adapted for piercing skin and sucking blood. (some authorities use the name Aphaniptera because it is older, but names above family rank need not follow the ICZN rules of priority, so most taxonomists use the more familiar name). Fleas are external parasites, living by hematophagy off the blood of mammals and birds. Genetic and morphological evidence indicates that they are descendants of the Scorpionfly family Boreidae, which are also flightless; accordingly it is possible that they will eventually be reclassified as a suborder within the Mecoptera. In the past, however, it was most commonly supposed that fleas had evolved from the flies (Diptera), based on similarities of the larvae. In any case, all these groups seem to represent a clade of closely related insect lineages, for which the names Mecopteroidea and Antliophora have been proposed.
The Goliath beetles are among the largest insects on Earth, if measured in terms of size, bulk and weight. They are members of subfamily Cetoniinae, within the scarab beetle family. Goliath beetles can be found in many of Africas tropical forests, where they feed primarily on tree sap and fruit. Little appears to be known of the larval cycle in the wild, but in captivity, Goliathus beetles have been successfully reared from egg to adult using protein-rich foods such as commercial cat and dog food. Goliath beetles measure from 60-110 millimetres (2.4-4.3 in) for males and 50-80 millimetres (2.0-3.1 in) for females, as adults, and can reach weights of up to 80-100 grams (2.8-3.5 oz) in the larval stage, though the adults are only about half this weight. The females range from a dark brown to silky white, but the males are normally brown/white/black or black/white.
Mosquito is a common flying insect in the family Culicidae that is found around the world. There are about 3,500 species of mosquitoes. They have a pair of scaled wings, a pair of halteres, a slender body, and six long legs. The females of most mosquito species suck blood (hematophagy) from other animals, which has made them the deadliest disease vector known, killing millions of people over thousands of years and continuing to kill millions per year by the spread of infectious diseases.
True flies are insects of the order Diptera (Greek: di = two, and pteron = wing), possessing a single pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax.
The presence of a single pair of wings distinguishes true flies from other insects with «fly» in their name, such as mayflies, dragonflies, damselflies, stoneflies, whiteflies, fireflies, alderflies, dobsonflies, snakeflies, sawflies, caddisflies, butterflies or scorpionflies. Some true flies have become secondarily wingless, especially in the superfamily Hippoboscoidea, or among those that are inquilines in social insect colonies.
Diptera is a large order, containing an estimated 240,000 species of mosquitos, gnats, midges and others, although under half of these (about 120,000 species) have been described. It is one of the major insect orders both in terms of ecological and human (medical and economic) importance. The Diptera, in particular the mosquitoes (Culicidae), are of great importance as disease transmitters, acting as vectors for malaria, dengue, West Nile virus, yellow fever, encephalitis and other infectious diseases.
Ants are social insects of the family Formicidae, and along with the related wasps and bees, they belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. Today, more than 12,000 species are classified with upper estimates of about 14,000 species. They are easily identified by their elbowed antennae and a distinctive node-like structure that forms a slender waist.
Ants form colonies that range in size from a few dozen predatory individuals living in small natural cavities to highly organised colonies which may occupy large territories and consist of millions of individuals. These larger colonies consist mostly of sterile wingless females forming castes of «workers», «soldiers», or other specialised groups. Nearly all ant colonies also have some fertile males called «drones» and one or more fertile females called «queens». The colonies are sometimes described as superorganisms because the ants appear to operate as a unified entity, collectively working together to support the colony.
Ants have colonised almost every landmass on Earth. The only places lacking indigenous ants are Antarctica and certain remote or inhospitable islands. Ants thrive in most ecosystems, and may form 15-25% of the terrestrial animal biomass. Their success has been attributed to their social organisation and their ability to modify habitats, tap resources, and defend themselves. Their long co-evolution with other species has led to mimetic, commensal, parasitic, and mutualistic relationships.
Ant societies have division of labour, communication between individuals, and an ability to solve complex problems. These parallels with human societies have long been an inspiration and subject of study.
Many human cultures make use of ants in cuisine, medication and rituals. Some species are valued in their role as biological pest control agents. However, their ability to exploit resources brings ants into conflict with humans, as they can damage crops and invade buildings. Some species, such as the red imported fire ant, are regarded as invasive species, since they have established themselves in new areas where they have been accidentally introduced.
Coccinellidae is a family of beetles, known variously as ladybirds (British English, Australian English, South African English), ladybugs (North American English) or lady beetles (preferred by some scientists). Lesser-used names include ladyclock, lady cow, and lady fly and Scarlet.
They are small insects, ranging from 1 mm to 10 mm (0.04 to 0.4 inches), and are commonly yellow, orange, or scarlet with small black spots on their wing covers, with black legs, head and antennae. A very large number of species are mostly or entirely black, grey, or brown and may be difficult for non-entomologists to recognize as coccinellids (and, conversely, there are many small beetles that are easily mistaken as such, like tortoise beetles).
Coccinellids are found worldwide, with over 5,000 species described, more than 450 native to North America alone.
A few species are pests in North America and Europe, but they are generally considered useful insects as many species feed on aphids or scale insects, which are pests in gardens, agricultural fields, orchards, and similar places. The Mall of America, for instance, releases thousands of ladybugs into its indoor park as a natural means of pest control for its gardens.
Bees are flying insects closely related to wasps and ants, and are known for their roles of producing honey and beeswax and pollination. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila. There are nearly 20,000 known species of bees in nine recognized families, though many are undescribed and the actual number is probably higher. They are found on every continent except Antarctica, in every habitat on the planet that contains insect-pollinated flowering plants.
Stag beetles are a group of about 1,200 species of beetle in the family Lucanidae, presently classified in four subfamilies Some species grow to 8 cm (3¼ in), but most are about 5 cm (2 in).
The English name is derived from the large and distinctive mandibles found on the males of most species, which resemble the antlers of stags.
A well-known species in much of Europe is Lucanus cervus, referred to in the United Kingdom as «the» stag beetle (it is the largest terrestrial insect in the UK). Pliny the Elder noted that Nigidius called the stag beetle lucanus after the Italian region of Lucania where they were used as amulets. The scientific name of Lucanus cervus is this word, plus cervus, deer.
Male stag beetles use their jaws to wrestle each other for favoured mating sites, but despite their often fearsome appearance they are not normally aggressive to humans. Stag beetles or Kuwagatamushi are sometimes used in the Asian sport of insect fighting.
Female stag beetles are usually smaller than the males, with smaller mandibles.
The larvae feed for several years on rotting wood, growing into grubs which in larger species may be the size of a human finger.
A dragonfly is a type of insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera. It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body. Dragonflies are similar to damselflies, but the adults can be differentiated by the fact that the wings of most dragonflies are held away from, and perpendicular to, the body when at rest. Even though dragonflies possess 6 legs like any other insect, they are not capable of walking.
Dragonflies are valuable predators that eat mosquitoes, and other small insects like flies, bees, ants, and butterflies. They are usually found around lakes, ponds, streams and wetlands because their larvae, known as «nymphs», are aquatic.
Nymphs can deliver a painful bite when threatened. The wound should be cleaned thoroughly to prevent water-borne infections.
Cockroaches (or simply «roaches») are insects of the order Blattaria. This name derives from the Latin word for «cockroach», Barata.
There are about 4,000 species of cockroach, of which 30 species are associated with human habitations and about four species are well known as pests.
Among the best-known pest species are the American cockroach, Periplaneta americana, which is about 30 millimetres (1.2 in) long, the German cockroach, Blattella germanica, about 15 millimetres (0.59 in) long, the Asian cockroach, Blattella asahinai, also about 15 millimetres (0.59 in) in length, and the Oriental cockroach, Blatta orientalis, about 25 millimetres (0.98 in). Tropical cockroaches are often much bigger, and extinct cockroach relatives such as the Carboniferous Archimylacris and the Permian Apthoroblattina were several times as large as these.
The termites are a group of social insects usually classified at the taxonomic rank of order Isoptera (but see also taxonomy below). As truly social animals, they are termed eusocial along with the ants and some bees and wasps which are all placed in the separate order Hymenoptera. Termites mostly feed on dead plant material, generally in the form of wood, leaf litter, soil, or animal dung, and about 10% of the estimated 4,000 species (about 2,600 taxonomically known) are economically significant as pests that can cause serious structural damage to buildings, crops or plantation forests. Termites are major detrivores, particularly in the subtropical and tropical regions, and their recycling of wood and other plant matter is of considerable ecological importance.
As eusocial insects, termites live in colonies that, at maturity, number from several hundred to several million individuals. They are a prime example of decentralised, self-organised systems using swarm intelligence and use this cooperation to exploit food sources and environments that could not be available to any single insect acting alone. A typical colony contains nymphs (semi-mature young), workers, soldiers, and reproductive individuals of both genders, sometimes containing several egg-laying queens.
Aphis is a genus of insects in the family Aphididae containing about 400 species of aphids. It includes many notorious agricultural pests, such as the soybean aphid A. glycines. Many Aphis, such as A. coreopsidis, are myrmecophiles, forming close associations with ants.
The Phasmatodea (sometimes called Phasmida) are an order of insects, whose members are variously known as stick insects (in Europe), walking sticks or stick-bugs (in the United States), phasmids, ghost insects and leaf insects (generally the family Phylliidae). The ordinal name is derived from the Greek «phasma» meaning an apparition or phantom, and refers to the resemblance of many species to sticks or leaves. Their natural camouflage can make them extremely difficult to spot.
Spiders (order Araneae) are chelicerate arthropods that have eight legs, and chelicerae modified into fangs that inject venom. Spiders are found world-wide on every continent except for Antarctica, and have become established in nearly every ecological niche with the exception of air and sea colonization. As of 2008, approximately 40,000 spider species, and 109 families have been recorded by taxonomists. However, there has been confusion within the scientific community as to how all these genera should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.
Anatomically, spiders differ from other arthropods in that the usual body segments are fused into two tagmata, the cephalothorax and abdomen, and joined by a small, cylindrical pedicel. In all except the most primitive group, the Mesothelae, spiders have the most centralized nervous systems of all arthropods, as all their ganglia are fused into one mass in the cephalothorax. Unlike most arthropods, spiders have no extensor muscles in their limbs and instead extend them by hydraulic pressure.
Their abdomens bear appendages that have been modified into spinnerets that extrude silk from up to six types of silk gland within their abdomens. Spiders webs vary widely in size, shape and the amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms, and spiders that produce tangled cobwebs are more abundant and diverse than orb-web spiders. Spider-like arachnids with silk-producing spigots appear in the Devonian period about 386 million years ago, but these animals apparently lacked spinnerets. True spiders have been found in Carboniferous rocks from 318 to 299 million years ago, and are very similar to the most primitive surviving order, the Mesothelae. The main groups of modern spiders, Mygalomorphae and Araneomorphae, first appear in the Triassic period, before 200 million years ago.
Dytiscidae — based on the Greek dytikos (δυτικός), «able to dive» — are the predaceous diving beetles, a family of water beetles. They are about 25 mm (one inch) long on average, though there is much variation between species. Dytiscus latissimus, the largest, can grow up to 45 mm long. Most are dark brown, blackish or dark olive in color with golden highlights in some subfamilies. They have short, but sharp mandibles. Immediately upon biting they deliver digestive enzymes. The larvae are commonly known as water tigers. The family has not been comprehensively cataloged since 1920, but is estimated to include about 4,000 species in over 160 genera.
Tick is the common name for the small arachnids in superfamily Ixodoidea that, along with other mites, constitute the Acarina. Ticks are ectoparasites (external parasites), living by hematophagy on the blood of mammals, birds, and occasionally reptiles and amphibians. Ticks are vectors of a number of diseases, including Lyme disease, Q fever, Colorado tick fever, tularemia, tick-borne relapsing fever, babesiosis, ehrlichiosis and Tick-borne meningoencephalitis, as well as anaplasmosis in cattle and canine jaundice.
Young ticks have six legs, and mature ticks have eight legs. They vary in size and appearance depending on the species.
Hemiptera is an order of insects, comprising around 80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others. They range in size from 1 mm to around 15 cm, and share a common arrangement of sucking mouthparts.
Chilopoda is then split into two clades: the Notostigmomorpha including the Scutigeromorpha and the Pluerostigmomorpha including the other four orders. The main difference is that the Notostigmomorpha have their spiracles located mid-dorsally. It was previously believed that Chilopoda was split into Anamorpha including the Lithobiomorpha and the Scutigeromorpha, and Epimorpha including the Geophilomorpha and Scolopendromorpha based on developmental modes, with the relationship of Craterostigmomorpha being uncertain. Recent phylogenetic analyses using combined molecular and morphological characters supports the previous phylogeny. The Epimorpha group still exists as monophyletic within the Pleurostigmomorpha, but the Anamorpha group is paraphyletic.
The more primitive of the Epimorpha, the Scolopendromorpha comprise 21 or more segments with the same number of paired legs. Their antennae have 17 or more segments. Their eyes will have at least 4 facets on each side.
The family Gerridae contains insects commonly known as water striders, water bugs, magic bugs, pond skaters, skaters, skimmers, water scooters, water skaters, water skeeters, water skimmers or water skippers. There are around 500 known species, commonly placed in around 60 genera.
Crickets, family Gryllidae (also known as «true crickets»), are insects somewhat related to grasshoppers and more closely related to katydids or bush crickets (family Tettigoniidae). They have somewhat flattened bodies and long antennae. There are about 900 species of crickets. They tend to be nocturnal and are often confused with grasshoppers because they have a similar body structure including jumping hind legs.
Locust is the swarming phase of short-horned grasshoppers of the family Acrididae. The origin and apparent extinction of certain species of locust-some of which reached 6 inches (15 cm) in length-are unclear.
These are species that can breed rapidly under suitable conditions and subsequently become gregarious and migratory. They form bands as nymphs and swarms as adults-both of which can travel great distances, rapidly stripping fields and greatly damaging crops.