Odonata
Odonata is an order of carnivorous insects, encompassing the dragonflies and the damselflies. The Odonata form a clade. Dragonflies are larger, perch with their wings held out to the sides. Fabricius coined the term Odonata from the Ancient Greek ὀδών odṓn'tooth' because they have teeth on their mandibles though most insects have toothed mandibles; the word dragonfly is sometimes used to refer to all Odonata, but odonate is a more correct English name for the group as a whole. Odonata enthusiasts avoid ambiguity by using the term true dragonfly, or Anisopteran, when referring to just the Anisoptera; the term Warriorfly has been proposed. Some 5,900 species have been described in this order; this order has traditionally been grouped together with the mayflies and several extinct orders in a group called the "Paleoptera", but this grouping might be paraphyletic. What they do share with mayflies is the nature of how the wings are articulated and held in rest. In some treatments, the Odonata are understood in an expanded sense synonymous with the superorder Odonatoptera but not including the prehistoric Protodonata.
In this approach, instead of Odonatoptera, the term Odonatoidea is used. The systematics of the "Palaeoptera" are by no means resolved; the Anisoptera was long treated as a suborder, with a third suborder, the "Anisozygoptera". However, the combined suborder Epiprocta was proposed when it was found that the "Anisozygoptera" was paraphyletic, composed of extinct offshoots of dragonfly evolution; the four living species placed in that group are in the infraorder Epiophlebioptera, whereas the fossil taxa that were there are now dispersed about the Odonatoptera. World Odonata List considers Anisoptera as a suborder along with Zygoptera and Anisozygoptera as well-understood and preferred terms. Tarsophlebiidae is a prehistoric family of Odonatoptera that can be considered either a basal lineage of Odonata or their immediate sister taxon; the phylogenetic tree of the orders and suborders of odonates according to Bechly: The largest living odonate is the giant Central American helicopter damselfly Megaloprepus coerulatus with a wing span of 191 mm.
The heaviest living odonates are Tetracanthagyna plagiata with a wing span of 165 mm, Petalura ingentissima with a body length of 117 mm and wing span of 160 mm. The longest extant odonate is the Neotropical helicopter damselfly Mecistogaster linearis with a body length of 135 mm. Sometimes the giant Hawaiian darner Anax strenuus is claimed to be the largest living odonate with an alleged wing span of 190 mm, but this seems to be rather a myth as only 152 mm are scientifically documented. Odonata and their ancestors come from one of the oldest winged insect groups; the fossils of odonates and their cousins Paleozoic "giant dragonflies" like Meganeuropsis permiana from the Permian of North America with up to 71 cm wing span and 43 cm body length have been the largest insects of all times and belonged to the order Meganisoptera, the griffinflies, related to odonates but not part of the modern order Odonata in the restricted sense have one of the most complete records going back 319 million years ago.
The smallest living dragonfly is Nannophya pygmaea from east Asia, which a body length of 15 mm and a wing span of 20 mm, the smallest damselflies are species of the genus Agriocnemis with a wing span of only 17–18 mm. These insects characteristically have large rounded heads covered by well-developed, compound eyes, legs that facilitate catching prey in flight, two pairs of long, transparent wings that move independently, elongated abdomens, they have short antennae. The mouthparts include simple chewing mandibles in the adult. Flight in the Odonata is direct, with flight muscles attaching directly to the wings; this allows active control of the amplitude, angle of attack and twist of each of the four wings independently. In most families there is a structure on the leading edge near the tip of the wing called the pterostigma; this is a thickened, hemolymph–filled and colorful area bounded by veins. The functions of the pterostigma are not known, but it most has an aerodynamic effect and may have a visual function.
More mass at the end of the wing may reduce the energy needed to move the wings up and down. The right combination of wing stiffness and wing mass could reduce the energy consumption of flying. A pterostigma is found among other insects, such as bees; the nymphs have stockier, bodies than the adults. In addition to lacking wings, their eyes are smaller, their antennae longer, their heads are less mobile than in the adult, their mouthparts are modified, with the labium being adapted into a unique prehensile organ for grasping prey. Damselfly nymphs breathe through external gills on the abdomen, while dragonfly nymphs respire through an organ in their rectum. Although generally
Holometabolism
Holometabolism called complete metamorphosis, is a form of insect development which includes four life stages: egg, larva and imago or adult. Holometabolism is a synapomorphic trait of all insects in the superorder Endopterygota. Immature stages of holometabolous insects are different from the mature stage. In some species the holometabolous life cycle prevents larvae from competing with adults because they inhabit different ecological niches; the morphology and behavior of each stage are adapted for different activities. For example, larval traits maximize feeding and development, while adult traits enable dispersal and egg laying; some species of holometabolous insects feed their offspring. Other insect developmental strategies include hemimetabolism. There are each with its own morphology and function; the first stage of the insect life cycle is the embryo, for all developmental strategies. The egg begins as a single cell which develops into the larval form before hatching; some insects reproduce by parthenogenesis or may be haplodiploid, produce viable eggs without fertilization.
The egg stage in most insects is short, only a few days. However, insects may hibernate, or undergo diapause in the egg stage to avoid extreme conditions, in which case this stage can last several months; the eggs of some types of insects, such as tsetse flies, or aphids, which hatch before they are laid. The second stage of the holometabolous life cycle is the larva. Many adult insects lay their eggs directly onto a food source so the larvae may begin eating as soon as they hatch. Larvae never possess wings or wing buds, have simple rather than compound eyes. In most species, the larval stage is worm-like in form. Larvae can be classified by their body type: Elateriform: wireworm-like, as in the beetle family Elateridae. Eruciform: caterpillar-like, as in the Lepidoptera and Symphyta; some that lack legs, such as the larvae of Nematoceran flies such as mosquitoes, are called apodous eruciform. Scarabaeiform: grub-like, with a head-capsule, as in the beetle family Scarabaeidae. Vermiform: maggot-like, as in most species of Brachyceran flies.
Campodeiform: similar to members of the genus Campodea, more or less straight and active, with functional legs. The larval stage is variously adapted to gaining and accumulating the materials and energy necessary for growth and metamorphosis. Most holometabolous insects pass through several larval stages, or instars, as they grow and develop; the larva must moult to pass from each larval stage. These stages may look similar and differ in size, or may differ in many characteristics including, color and spines, number of legs. Differences between larval stages are pronounced in insects with hypermetamorphosis; the final larval stage in some insects is called a prepupa. Prepupae do not feed, become inactive. To enter the third stage of homometabolous development, the larva undergoes metamorphosis into a pupa; the pupa is a non-feeding developmental stage. Most pupae move little, the pupae of some species, such as mosquitoes, are mobile. In preparation for pupation, the larvae of many species seek protected sites or construct a protective cocoon of silk or other material, such as its own accumulated feces.
Some insects undergo diapause as pupa. In this stage, the insect's physiology and functional structure, both internal and external, change drastically. Pupae can be classified into three types: obtect and coarctate. Obtect pupae are compact, with the legs and other appendages enclosed, such as a butterfly chrysalis. Exarate pupae have other appendages free and extended. Coarctate pupae develop inside the larval skin; the final stage of holometabolous insect development is imago. Most adult insects have functioning reproductive organs. Most adult insects grow little after eclosion from the pupa; some adult insects do not feed at all, focus on mating and reproduction. Around 45% to 60% of all known living species are holometabolan insects. Juveniles and adult forms of holometabolan insects occupy different ecological niches, exploiting different resources; this fact is considered a key driver in the unusual evolutionary diversification of form and physiology within this group. According to the latest phylogenetic reconstructions, holometabolan insects are monophyletic, which suggests that the evolutionary innovation of complete metamorphosis occurred only once.
Paleontological evidence shows. Carboniferous fossil samples display a remarkable diversity of species with functional wings; these fossil remains show that the primitive Apterygota and the ancient winged insects were ametabolous. By the end of the Carboniferous, into the Permian, most pterygotes had post-embryonic development which included separated nymphal and adult stages, which shows that hemimetaboly had evolved; the earliest known fossil insects that can be considered holometabolan appear in the Permian strata. Phylogenetic studies show that the sister group of Endopterygota is paraneoptera, which includes hemimetabolan species and a number of neometabolan groups; the most parsimonious evolutionary hypothesis is that holometabolans originated from hemimetabolan ancestors. The origin of complete metamorphosis in insects has been the subject of a long lasting, at times fierce, debate. One of the first theories proposed was one by William H
Eye
Eyes are organs of the visual system. They provide organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes convert it into electro-chemical impulses in neurons. In higher organisms, the eye is a complex optical system which collects light from the surrounding environment, regulates its intensity through a diaphragm, focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, transmits these signals to the brain through complex neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain. Eyes with resolving power have come in ten fundamentally different forms, 96% of animal species possess a complex optical system. Image-resolving eyes are present in molluscs and arthropods; the simplest "eyes", such as those in microorganisms, do nothing but detect whether the surroundings are light or dark, sufficient for the entrainment of circadian rhythms.
From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment and to the pretectal area to control the pupillary light reflex. Complex eyes can distinguish colours; the visual fields of many organisms predators, involve large areas of binocular vision to improve depth perception. In other organisms, eyes are located so as to maximise the field of view, such as in rabbits and horses, which have monocular vision; the first proto-eyes evolved among animals 600 million years ago about the time of the Cambrian explosion. The last common ancestor of animals possessed the biochemical toolkit necessary for vision, more advanced eyes have evolved in 96% of animal species in six of the ~35 main phyla. In most vertebrates and some molluscs, the eye works by allowing light to enter and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye; the cone cells and the rod cells in the retina detect and convert light into neural signals for vision.
The visual signals are transmitted to the brain via the optic nerve. Such eyes are roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and an iris; the eyes of most cephalopods, fish and snakes have fixed lens shapes, focusing vision is achieved by telescoping the lens—similar to how a camera focuses. Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the details of anatomy, may give either a single pixelated image or multiple images, per eye; each sensor has its own photosensitive cell. Some eyes have up to 28,000 such sensors, which are arranged hexagonally, which can give a full 360° field of vision. Compound eyes are sensitive to motion; some arthropods, including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an image, creating vision. With each eye viewing a different thing, a fused image from all the eyes is produced in the brain, providing different, high-resolution images.
Possessing detailed hyperspectral colour vision, the Mantis shrimp has been reported to have the world's most complex colour vision system. Trilobites, which are now extinct, had unique compound eyes, they used clear calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods; the number of lenses in such an eye varied, however: some trilobites had only one, some had thousands of lenses in one eye. In contrast to compound eyes, simple eyes are those. For example, jumping spiders have a large pair of simple eyes with a narrow field of view, supported by an array of other, smaller eyes for peripheral vision; some insect larvae, like caterpillars, have a different type of simple eye which provides only a rough image, but can possess resolving powers of 4 degrees of arc, be polarization sensitive and capable of increasing its absolute sensitivity at night by a factor of 1,000 or more. Some of the simplest eyes, called ocelli, can be found in animals like some of the snails, which cannot "see" in the normal sense.
They do have photosensitive cells, but no lens and no other means of projecting an image onto these cells. They can no more; this enables snails to keep out of direct sunlight. In organisms dwelling near deep-sea vents, compound eyes have been secondarily simplified and adapted to spot the infra-red light produced by the hot vents—in this way the bearers can spot hot springs and avoid being boiled alive. There are ten different eye layouts—indeed every technological method of capturing an optical image used by human beings, with the exceptions of zoom and Fresnel lenses, occur in nature. Eye types can be categorised into "simple eyes", with one concave photoreceptive surface, "compound eyes", which comprise a number of individual lenses laid out on a convex surface. Note that "simple" does not imply a reduced level of complexity or acuity. Indeed, any eye type can be adapted for any behaviour or environment; the only limitations specific to eye types are that of resolution—the physics of compound eyes prevents them from achieving a resolution better than 1°.
Superposition eyes can achieve greater sensitivity than apposition eyes, so are better suited to
Compound eye
A compound eye is a visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidia, which are tiny independent photoreception units that consist of a cornea and photoreceptor cells which distinguish brightness and color; the image perceived by the arthropod is a combination of inputs from the numerous ommatidia, which are oriented to point in different directions. Compared with single-aperture eyes, compound eyes have poor image resolution. Compound eyes are classified as either apposition eyes, which form multiple inverted images, or superposition eyes, which form a single erect image. Apposition eyes can be divided into two groups; the typical apposition eye has a lens focusing light from one direction on the rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium. The mantis shrimp is the most advanced example of an animal with this type of eye. In the other kind of apposition eye, found in the Strepsiptera, each lens forms an image, the images are combined in the brain.
This is called the neural superposition eye. The second type is named the superposition eye; the superposition eye is divided into three types. The refracting superposition eye has a gap between the lens and the rhabdom, no side wall; each lens reflects it to the same angle on the other side. The result is an image at half the radius of the eye, where the tips of the rhabdoms are; this kind is used by nocturnal insects. In the parabolic superposition compound eye type, seen in arthropods such as mayflies, the parabolic surfaces of the inside of each facet focus light from a reflector to a sensor array. Long-bodied decapod crustaceans such as shrimp, prawns and lobsters are alone in having reflecting superposition eyes, which have a transparent gap but use corner mirrors instead of lenses. Good fliers like flies or honey bees, or prey-catching insects like praying mantis or dragonflies, have specialized zones of ommatidia organized into a fovea area which gives acute vision. In the acute zone the eye is flattened and the facets larger.
The flattening allows more ommatidia to receive light from a spot and therefore higher resolution. There are some exceptions from the types mentioned above; some insects have a so-called single lens compound eye, a transitional type, something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. There is the mysid shrimp, Dioptromysis paucispinosa; the shrimp has an eye of the refracting superposition type, in the rear behind this in each eye there is a single large facet, three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialized retina; the resulting eye is a mixture of a simple eye within a compound eye. Another version is the pseudofaceted eye; this type of eye consists of a cluster of numerous ocelli on each side of the head, organized in a way that resembles a true compound eye. The body of Ophiocoma wendtii, a type of brittle star, was thought to be covered with ommatidia, turning its whole skin into a compound eye.
Asymmetries in compound eyes may be associated with asymmetries in behaviour. For example, Temnothorax albipennis ant scouts show behavioural lateralization when exploring unknown nest sites, showing a population-level bias to prefer left turns. One possible reason for this is that its environment is maze-like and turning in one direction is a good way to search and exit mazes without getting lost; this turning bias is correlated with slight asymmetries in the ants' compound eyes. Pseudopupil Arthropod eye Ommatidium Eye Media related to Compound eye at Wikimedia Commons The Compound Eye Make Your Own Compound Eye by Stephanie Bailey Did you know that shrimps blink
Anatomical terms of location
Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. All vertebrates have the same basic body plan – they are bilaterally symmetrical in early embryonic stages and bilaterally symmetrical in adulthood; that is, they have mirror-image left and right halves if divided down the middle. For these reasons, the basic directional terms can be considered to be those used in vertebrates. By extension, the same terms are used for many other organisms as well. While these terms are standardized within specific fields of biology, there are unavoidable, sometimes dramatic, differences between some disciplines. For example, differences in terminology remain a problem that, to some extent, still separates the terminology of human anatomy from that used in the study of various other zoological categories. Standardized anatomical and zoological terms of location have been developed based on Latin and Greek words, to enable all biological and medical scientists to delineate and communicate information about animal bodies and their component organs though the meaning of some of the terms is context-sensitive.
The vertebrates and Craniata share a substantial heritage and common structure, so many of the same terms are used for location. To avoid ambiguities this terminology is based on the anatomy of each animal in a standard way. For humans, one type of vertebrate, anatomical terms may differ from other forms of vertebrates. For one reason, this is because humans have a different neuraxis and, unlike animals that rest on four limbs, humans are considered when describing anatomy as being in the standard anatomical position, thus what is on "top" of a human is the head, whereas the "top" of a dog may be its back, the "top" of a flounder could refer to either its left or its right side. For invertebrates, standard application of locational terminology becomes difficult or debatable at best when the differences in morphology are so radical that common concepts are not homologous and do not refer to common concepts. For example, many species are not bilaterally symmetrical. In these species, terminology depends on their type of symmetry.
Because animals can change orientation with respect to their environment, because appendages like limbs and tentacles can change position with respect to the main body, positional descriptive terms need to refer to the animal as in its standard anatomical position. All descriptions are with respect to the organism in its standard anatomical position when the organism in question has appendages in another position; this helps avoid confusion in terminology. In humans, this refers to the body in a standing position with arms at the side and palms facing forward. While the universal vertebrate terminology used in veterinary medicine would work in human medicine, the human terms are thought to be too well established to be worth changing. Many anatomical terms can be combined, either to indicate a position in two axes or to indicate the direction of a movement relative to the body. For example, "anterolateral" indicates a position, both anterior and lateral to the body axis. In radiology, an X-ray image may be said to be "anteroposterior", indicating that the beam of X-rays pass from their source to patient's anterior body wall through the body to exit through posterior body wall.
There is no definite limit to the contexts in which terms may be modified to qualify each other in such combinations. The modifier term is truncated and an "o" or an "i" is added in prefixing it to the qualified term. For example, a view of an animal from an aspect at once dorsal and lateral might be called a "dorsolateral" view. Again, in describing the morphology of an organ or habitus of an animal such as many of the Platyhelminthes, one might speak of it as "dorsiventrally" flattened as opposed to bilaterally flattened animals such as ocean sunfish. Where desirable three or more terms may be agglutinated or concatenated, as in "anteriodorsolateral"; such terms sometimes used to be hyphenated. There is however little basis for any strict rule to interfere with choice of convenience in such usage. Three basic reference planes are used to describe location; the sagittal plane is a plane parallel to the sagittal suture. All other sagittal planes are parallel to it, it is known as a "longitudinal plane".
The plane is perpendicular to the ground. The median plane or midsagittal plane is in the midline of the body, divides the body into left and right portions; this passes through the head, spinal cord, and, in many animals, the tail. The term "median plane" can refer to the midsagittal plane of other structures, such as a digit; the frontal plane or coronal plane divides the body into ventral portions. For post-embryonic humans a coronal plane is vertical and a transverse plane is horizontal, but for embryos and quadrupeds a coronal plane is horizontal and a transverse plane is vertical. A longitudinal plane is any plane perpendicular to the transverse plane; the coronal plane and the sagittal plane are examples of longitudinal planes. A transverse plane known as a cross-section, divides the body into cranial and caudal portions. In human anatomy: A transverse plane is an X-Z plane, parallel to the ground, which s
Cnidaria
Cnidaria is a phylum under Kingdom Animalia containing over 11,000 species of animals found in aquatic environments: they are predominantly marine. Their distinguishing feature is cnidocytes, specialized cells that they use for capturing prey, their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are one cell thick. They have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Both forms have a single body cavity that are used for digestion and respiration. Many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both. Cnidarians' activities are coordinated by simple receptors. Several free-swimming species of Cubozoa and Scyphozoa possess balance-sensing statocysts, some have simple eyes. Not all cnidarians reproduce sexually, with many species having complex life cycles of asexual polyp stages and sexual medusae.
Some, omit either the polyp or the medusa stage. Cnidarians were grouped with ctenophores in the phylum Coelenterata, but increasing awareness of their differences caused them to be placed in separate phyla. Cnidarians are classified into four main groups: the wholly sessile Anthozoa. Staurozoa have been recognised as a class in their own right rather than a sub-group of Scyphozoa, the parasitic Myxozoa and Polypodiozoa were only recognized as cnidarians in 2007. Most cnidarians prey on organisms ranging in size from plankton to animals several times larger than themselves, but many obtain much of their nutrition from dinoflagellates, a few are parasites. Many are preyed on by other animals including starfish, sea slugs, fish and other cnidarians. Many scleractinian corals—which form the structural foundation for coral reefs—possess polyps that are filled with symbiotic photo-synthetic zooxanthellae. While reef-forming corals are entirely restricted to warm and shallow marine waters, other cnidarians can be found at great depths, in polar regions, in freshwater.
Recent phylogenetic analyses support monophyly of cnidarians, as well as the position of cnidarians as the sister group of bilaterians. Fossil cnidarians have been found in rocks formed about 580 million years ago, other fossils show that corals may have been present shortly before 490 million years ago and diversified a few million years later. However, molecular clock analysis of mitochondrial genes suggests a much older age for the crown group of cnidarians, estimated around 741 million years ago 200 million years before the Cambrian period as well as any fossils. Cnidarians form a phylum of animal that are more complex than sponges, about as complex as ctenophores, less complex than bilaterians, which include all other animals. Both cnidarians and ctenophores are more complex than sponges as they have: cells bound by inter-cell connections and carpet-like basement membranes. Cnidarians are distinguished from all other animals by having cnidocytes that fire harpoon like structures and are used to capture prey.
In some species, cnidocytes can be used as anchors. Like sponges and ctenophores, cnidarians have two main layers of cells that sandwich a middle layer of jelly-like material, called the mesoglea in cnidarians. Hence and ctenophores have traditionally been labelled diploblastic, along with sponges. However, both cnidarians and ctenophores have a type of muscle that, in more complex animals, arises from the middle cell layer; as a result, some recent text books classify ctenophores as triploblastic, it has been suggested that cnidarians evolved from triploblastic ancestors. Most adult cnidarians appear as either free-swimming medusae or sessile polyps, many hydrozoans species are known to alternate between the two forms. Both are radially symmetrical, like a tube respectively. Since these animals have no heads, their ends are described as "oral" and "aboral". Most have fringes of tentacles equipped with cnidocytes around their edges, medusae have an inner ring of tentacles around the mouth; some hydroids may consist of colonies of zooids that serve different purposes, such as defense and catching prey.
The mesoglea of polyps is thin and soft, but that of medusae is thick and springy, so that it returns to its original shape after muscles around the edge have contracted to squeeze water out, enabling medusae to swim by a sort of jet propulsion. In medusae the only supporting structure is the mesoglea. Hydra and most sea anemones close their mouths when they are not feeding, the water in the digestive cavity acts as a hydrostatic skeleton, rather like a water-filled balloon. Other polyps such as Tubularia use columns of water-filled cells for support. Sea pens stiffen the mesoglea with calcium carbonate spicules and tough fibrous proteins, rather like sponges. In some colonial polyps, a chitinous periderm gives support and some protection to the connecting sections and to the lower parts of individual polyps. Stony corals secrete massive calcium carbonate exoske
Wasp
A wasp is any insect of the order Hymenoptera and suborder Apocrita, neither a bee nor an ant. The Apocrita form a clade; the most known wasps, such as yellowjackets and hornets, are in the family Vespidae and are eusocial, living together in a nest with an egg-laying queen and non-reproducing workers. Eusociality is favoured by the unusual haplodiploid system of sex determination in Hymenoptera, as it makes sisters exceptionally related to each other. However, the majority of wasp species are solitary, with each adult female living and breeding independently. Females have an ovipositor for laying eggs in or near a food source for the larvae, though in the Aculeata the ovipositor is modified instead into a sting used for defense or prey capture. Wasps play many ecological roles; some are pollinators, whether to feed themselves or to provision their nests. Many, notably the cuckoo wasps, are kleptoparasites. Many of the solitary wasps are parasitoidal, meaning they lay eggs on or in other insects and provision their own nests with such hosts.
Unlike true parasites, the wasp larvae kill their hosts. Solitary wasps parasitize every pest insect, making wasps valuable in horticulture for biological pest control of species such as whitefly in tomatoes and other crops. Wasps first appeared in the fossil record in the Jurassic, diversified into many surviving superfamilies by the Cretaceous, they are a diverse group of insects with tens of thousands of described species. The largest social wasp is the Asian giant hornet, at up to 5 centimetres in length; the smallest wasps are solitary chalcid wasps in the family Mymaridae, including the world's smallest known insect, with a body length of only 0.139 mm, the smallest known flying insect, only 0.15 mm long. Wasps have appeared in literature from Classical times, as the eponymous chorus of old men in Aristophanes' 422 BC comedy Σφῆκες, The Wasps, in science fiction from H. G. Wells's 1904 novel The Food of the Gods and How It Came to Earth, featuring giant wasps with three-inch-long stings.
The name "Wasp" has been used for other military equipment. The wasps are a cosmopolitan paraphyletic grouping of hundreds of thousands of species, consisting of the narrow-waisted Apocrita without the ants and bees; the Hymenoptera contain the somewhat wasplike but unwaisted Symphyta, the sawflies. The term wasp is sometimes used more narrowly for the Vespidae, which includes the common wasp or yellow jacket genera Vespula and Dolichovespula and the hornets, Vespa. Hymenoptera in the form of Symphyta first appeared in the fossil record in the Lower Triassic. Apocrita, wasps in the broad sense, appeared in the Jurassic, had diversified into many of the extant superfamilies by the Cretaceous. Fig wasps with modern anatomical features first appeared in the Lower Cretaceous of the Crato Formation in Brazil, some 65 million years before the first fig trees; the Vespidae include the extinct genus Palaeovespa, seven species of which are known from the Eocene rocks of the Florissant fossil beds of Colorado and from fossilised Baltic amber in Europe.
Found in Baltic amber are crown wasps of the genus Electrostephanus. Wasps are a diverse group, estimated at over a hundred thousand described species around the world, a great many more as yet undescribed. For example, there are over 800 species of fig trees in the tropics, all of these has its own specific fig wasp to effect pollination. Many wasp species are parasitoids; some larvae start off as parasitoids, but convert at a stage to consuming the plant tissues that their host is feeding on. In other species, the eggs are laid directly into plant tissues and form galls, which protect the developing larvae from predators but not from other parasitic wasps. In some species, the larvae are predatory themselves; the largest social wasp is the Asian giant hornet, at up to 5 centimetres in length. The various tarantula hawk wasps are of a similar size and can overpower a spider many times its own weight, move it to its burrow, with a sting, excruciatingly painful to humans; the solitary giant scoliid, Megascolia procer, with a wingspan of 11.5 cm, has subspecies in Sumatra and Java.
The female giant ichneumon wasp Megarhyssa macrurus is 12.5 centimetres long including its long but slender ovipositor, used for boring into wood and inserting eggs. The smallest wasps are solitary chalcid wasps in the family Mymaridae, including the world's smallest known insect, Dicopomorpha echmepterygis and Kikiki huna with a body length of only 158 micrometres, the smallest known flying insect. There are estimated to be 100,000 species of ichneumonoid wasps in the families Braconidae and Ichneumonidae; these are exclusively parasitoids utilising other insects as hosts. Another family, the Pompilidae, is a specialist parasitoid of spiders; some wasps
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