The evolutionary ancestry of arthropods dates back to the Cambrian period. The group is generally regarded as monophyletic, and many analyses support the placement of arthropods with cycloneuralians (or their constituent clades) in a superphylum Ecdysozoa. Overall, however, the basal relationships of animals are not yet well resolved. Likewise, the relationships between various arthropod groups are still actively debated. Today, arthropods contribute to the human food supply both directly as food, and more importantly, indirectly as pollinators of crops. Some species are known to spread severe disease to humans, livestock, and crops. (Full article...)
The genus Anopheles diverged from other mosquitoes approximately 100 million years ago (mya), and, like other mosquitoes, the eggs, larvae, and pupae are aquatic. The Anopheles larva has no respiratory siphon through which to breathe, so it breathes and feeds with its body horizontal to the surface of the water. The adult mosquito hatches from the surface and feeds on the nectar of flowers; the female mosquito also feeds on blood, which animal diet allows them to carry and transmit parasites between hosts. The adult's feeding position is head-down, unlike the horizontal stance of the culicines. Anopheles are distributed almost worldwide, throughout the tropics, the subtropics, and the temperate regions of planet Earth. In hot weather, adult Anophelesaestivate, which is a state of dormancy that enables the mosquito to survive in hot dry regions, such as the Sahel. (Full article...)
Terropterus was the earliest known and largest mixopterid eurypterid. Fossil specimens referred to T. xiushanensis are estimated to have reached up to 40 centimeters (15.7 in) in length, but other fossils, either representing older T. xiushanensis or a second species of Terropterus, demonstrate that members of the genus could reach upwards of at least 100 centimeters (3.3 ft) in length. Terropterus is the only mixopterid known from the ancient southern continent of Gondwana, with the other two mixopterid genera, Mixopterus and Lanarkopterus, only being known from what was once the northern continent of Laurussia. The discovery of Terropterus significantly expanded the known geographical and temporal ranges of the Mixopteridae.
The deposits in which fossils of Terropterus were discovered were once a marine environment. Fossils of several other groups are known from the same deposits, including trilobites, brachiopods, gastropods and other eurypterids. Due to its large size and its predatory adaptations, including the characteristic mixopterid large and spiny forward-facing appendages, Terropterus was likely the apex predator of its marine ecosystem. (Full article...)
Eucteniza (/juːktəˈnaɪzə/yook-tə-NY-zə) is a genus of trapdoor spiders in the family Euctenizidae containing at least 14 species occurring in Mexico and the southern United States. Species are distinguished by a softened rear portion of the carapace, and males possess large spines on the first two pairs of walking legs that are used to hold females during mating. Like other trapdoor spiders they create burrows with a hinged lid, from which they await passing insects and other arthropods to prey upon. Many species are known from only one or two localities, or from only male specimens. More species are expected to be discovered. Eucteniza is closely related to spiders of the genera Entychides and Neoapachella. (Full article...)
Scale insects are small insects of the orderHemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than the superfamily Coccoidea due to taxonomic uncertainties. Adult females typically have soft bodies and no limbs, and are concealed underneath domed scales, extruding quantities of wax for protection. Some species are hermaphroditic, with a combined ovotestis instead of separate ovaries and testes. Males, in the species where they occur, have legs and sometimes wings, and resemble small flies. Scale insects are herbivores, piercing plant tissues with their mouthparts and remaining in one place, feeding on sap. The excess fluid they imbibe is secreted as honeydew on which sooty mold tends to grow. The insects often have a mutualistic relationship with ants, which feed on the honeydew and protect them from predators. There are about 8,000 described species.
The oldest fossils of the group date to the Early Cretaceous, preserved in amber. They were already substantially diversified by this time suggesting an earlier origin during the Triassic or Jurassic. Their closest relatives are the jumping plant lice, whiteflies, phylloxera bugs and aphids. The majority of female scale insects remain in one place as adults, with newly hatched nymphs, known as "crawlers", being the only mobile life stage, apart from the short-lived males. The reproductive strategies of many species include at least some amount of asexual reproduction by parthenogenesis.
Some scale insects are serious commercial pests, notably the cottony cushion scale (Icerya purchasi) on Citrus fruit trees; they are difficult to control as the scale and waxy covering protect them effectively from contact insecticides. Some species are used for biological control of pest plants such as the prickly pear, Opuntia. Others produce commercially valuable substances including carmine and kermes dyes, and shellac lacquer. The two red colour-names crimson and scarlet both derive from the names of Kermes products in other languages. (Full article...)
The Phasmatodea (also known as Phasmida or Phasmatoptera) are an order of insects whose members are variously known as stick insects, stick-bugs, walkingsticks, stick animals, or bug sticks. They are also occasionally referred to as Devil's darning needles, although this name is shared by both dragonflies and crane flies. They can be generally referred to as phasmatodeans, phasmids, or ghost insects, with phasmids in the family Phylliidae called leaf insects, leaf-bugs, walking leaves, or bug leaves. The group's name is derived from the Ancient Greekφάσμαphasma, meaning an apparition or phantom, referring to their resemblance to vegetation while in fact being animals. Their natural camouflage makes them difficult for predators to detect; still, many species have one of several secondary lines of defense in the form of startle displays, spines or toxic secretions. Stick insects from the genera Phryganistria, Ctenomorpha, and Phobaeticus include the world's longest insects.
Members of the order are found on all continents except Antarctica, but they are most abundant in the tropics and subtropics. They are herbivorous, with many species living unobtrusively in the tree canopy. They have an incomplete metamorphosis life cycle with three stages: egg, nymph and adult. Many phasmids are parthenogenic, and do not require fertilized eggs for female offspring to be produced. In hotter climates, they may breed all year round; in more temperate regions, the females lay eggs in the autumn before dying, and the new generation hatches in the spring. Some species have wings and can disperse by flying, while others are more restricted. (Full article...)
Cockroaches (or roaches) are insects belonging to the orderBlattodea (Blattaria). About 30 cockroach species out of 4,600 are associated with human habitats. Some species are well-known pests.
The cockroaches are an ancient group, with their ancestors, known as "roachoids", originating during the Carboniferous period, some 320 million years ago. Those early ancestors, however, lacked the internal ovipositors of modern roaches. Cockroaches are somewhat generalized insects lacking special adaptations (such as the sucking mouthparts of aphids and other true bugs); they have chewing mouthparts and are probably among the most primitive of living Neopteran insects. They are common and hardy insects capable of tolerating a wide range of climates, from Arctic cold to tropical heat. Tropical cockroaches are often much larger than temperate species.
Modern cockroaches are not considered to be a monophyletic group, as it has been found based on genetics that termites are deeply nested within the group, with some groups of cockroaches more closely related to termites than they are to other cockroaches, thus rendering Blattaria paraphyletic. Both cockroaches and termites are included into Blattodea. (Full article...)
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Insects are the only group of invertebrates that have evolved wings and flight. Insects first flew in the Carboniferous, some 300 to 350 million years ago, making them the first animals to evolve flight. Wings may have evolved from appendages on the sides of existing limbs, which already had nerves, joints, and muscles used for other purposes. These may initially have been used for sailing on water, or to slow the rate of descent when gliding.
Two insect groups, the dragonflies and the mayflies, have flight muscles attached directly to the wings. In other winged insects, flight muscles attach to the thorax, which make it oscillate in order to induce the wings to beat. Of these insects, some (flies and some beetles) achieve very high wingbeat frequencies through the evolution of an "asynchronous" nervous system, in which the thorax oscillates faster than the rate of nerve impulses.
Whale barnacles passively filter food, using tentacle-like cirri, as the host swims through the water. The arrangement is generally considered commensal as it is done at no cost or benefit to the host. However, some whales may make use of the barnacles as protective armor or for inflicting more damage while fighting, which would make the relationship mutualistic where both parties benefit; alternatively, some species may just increase the drag that the host experiences while swimming, making the barnacles parasites.
After hatching, whale barnacles go through six molting stages before searching for a host, being prompted to settle by a chemical cue from the host skin. The barnacle creates a crown-shaped shell, and in most instances, deeply embeds itself into the skin for stability while riding a fast-moving host. The shell plates are made of calcium carbonate and chitin. (Full article...)
Ants are eusocialinsects of the familyFormicidae and, along with the related wasps and bees, belong to the orderHymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22,000 species have been classified. They are easily identified by their geniculate (elbowed) antennae and the distinctive node-like structure that forms their slender waists.
Ants form colonies that range in size from a few dozen predatory individuals living in small natural cavities to highly organised colonies that may occupy large territories and consist of millions of individuals. Larger colonies consist of various castes of sterile, wingless females, most of which are workers (ergates), as well as soldiers (dinergates) and other specialised groups. Nearly all ant colonies also have some fertile males called "drones" and one or more fertile females called "queens" (gynes). The colonies are 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 a few remote or inhospitable islands. Ants thrive in moist tropical ecosystems and may exceed the combined biomass of wild birds and mammals. Their success in so many environments 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. (Full article...)
Mantises are an order (Mantodea) of insects that contains over 2,400 species in about 460 genera in 33 families. The largest family is the Mantidae ("mantids"). Mantises are distributed worldwide in temperate and tropical habitats. They have triangular heads with bulging eyes supported on flexible necks. Their elongated bodies may or may not have wings, but all Mantodea have forelegs that are greatly enlarged and adapted for catching and gripping prey; their upright posture, while remaining stationary with forearms folded, has led to the common name praying mantis.
The closest relatives of mantises are termites and cockroaches (Blattodea), which are all within the superorderDictyoptera. Mantises are sometimes confused with stick insects (Phasmatodea), other elongated insects such as grasshoppers (Orthoptera), or other more distantly related insects with raptorial forelegs such as mantisflies (Mantispidae). Mantises are mostly ambush predators, but a few ground-dwelling species are found actively pursuing their prey. They normally live for about a year. In cooler climates, the adults lay eggs in autumn, then die. The eggs are protected by their hard capsules and hatch in the spring. Females sometimes practice sexual cannibalism, eating their mates after copulation.
Drawing of the carapace of C. oculatus by its original descriptor, Stepan S. Kutorga (1838)
Campylocephalus is a genus of eurypterid, a group of extinct aquatic arthropods. Fossils of Campylocephalus have been discovered in deposits ranging from the Carboniferous period in the Czech Republic (the species C. salmi) to the Permian period of Russia (species C. oculatus and C. permianus). The generic name is composed of the Greek words καμπύλος (kampýlos), meaning "curved", and κεφαλή (kephalē), meaning "head".
It was a member of the hibbertopteridfamily of eurypterids and probably looked much the same as the other members of the family, Hibbertopterus and Vernonopterus, in that it was a large, broad and heavy animal quite different from the famous swimming eurypterids (such as Pterygotus and Eurypterus) which had been common during earlier periods. Like all other stylonurine eurypterids, Campylocephalus completely lacked swimming paddles.
Hibbertopterids such as Campylocephalus were, as many other families within the stylonurine suborder, sweep-feeders. Sweep-feeding food strategies involve specialized appendages with blades that could be used by the animals to rake through the substrate of their living environments in search for small prey items. (Full article...)
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Winged and wingless forms
Thrips (orderThysanoptera) are minute (mostly 1 mm (0.039 in) long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Entomologists have described approximately 7,700 species. They fly only weakly and their feathery wings are unsuitable for conventional flight; instead, thrips exploit an unusual mechanism, clap and fling, to create lift using an unsteady circulation pattern with transient vortices near the wings.
Thrips are a functionally diverse group, with nearly half of the known species being fungivorous. A small proportion of species of thrips are serious pests of commercially important crops. Some of these serve as vectors for over 20 viruses that cause plant disease, especially the Tospoviruses. Many flower-dwelling species bring benefits as pollinators, with some predatory thrips feeding on small insects or mites. In the right conditions, such as in greenhouses, invasive species can exponentially increase in population size and form large swarms because of a lack of natural predators coupled with their ability to reproduce asexually, making them destructive to crops. Due to their cryptic nature, thrips may aggregate in household objects such as furniture, bedding and computer monitors – in the latter case by forcing their way in between the LCD and its glass covering. Their identification to species by standard morphological characteristics is often challenging. (Full article...)
Insect wings are adult outgrowths of the insectexoskeleton that enable insects to fly. They are found on the second and third thoracic segments (the mesothorax and metathorax), and the two pairs are often referred to as the forewings and hindwings, respectively, though a few insects lack hindwings, even rudiments. The wings are strengthened by a number of longitudinal veins, which often have cross-connections that form closed "cells" in the membrane (extreme examples include the dragonflies and lacewings). The patterns resulting from the fusion and cross-connection of the wing veins are often diagnostic for different evolutionary lineages and can be used for identification to the family or even genus level in many orders of insects.
Physically, some insects move their flight muscles directly, others indirectly. In insects with direct flight, the wing muscles directly attach to the wing base, so that a small downward movement of the wing base lifts the wing itself upward. Those insects with indirect flight have muscles that attach to and deform the thorax, causing the wings to move as well.
The wings are present in only one sex (often the male) in some groups such as velvet ants and Strepsiptera, or are selectively lost in "workers" of social insects such as ants and termites. Rarely, the female is winged but the male not, as in fig wasps. In some cases, wings are produced only at particular times in the life cycle, such as in the dispersal phase of aphids. Wing structure and colouration often vary with morphs, such as in the aphids, migratory phases of locusts and polymorphic butterflies. At rest, the wings may be held flat, or folded a number of times along specific patterns; most typically, it is the hindwings which are folded, but in a few groups such as the vespid wasps, it is the forewings. (Full article...)
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Polistes exclamans, the Guinea paper wasp, is a socialwasp and is part of the family Vespidae of the order Hymenoptera. It is found throughout the United States, Mexico, the Bahamas, Jamaica and parts of Canada. Due to solitary nest founding by queens, P. exclamans has extended its range in the past few decades and now covers the eastern half of the United States, as well as part of the north. This expansion is typically attributed to changing global climate and temperatures. P. exclamans has three specific castes, including males, workers, and queens, but the dominance hierarchy is further distinguished by age. The older the wasp is, the higher it is in ranking within the colony. In most P. exclamans nests, there is one queen who lays all the eggs in the colony. The physiological similarities between the worker and queen castes have led to experiments attempting to distinguish the characteristics of these two castes and how they are determined, though males have easily identifiable physiological characteristics. Since P. exclamans live in relatively small, open combed nests, they are often subject to predators and parasites, such as Chalcoela iphitalis, Elasmus polistis, and birds. P. exclamans have defense and recognition strategies that help protect against these predators and parasites. (Full article...)
Image 7Mature queen of a termite colony, showing how the unsclerotised cuticle stretches between the dark sclerites that failed to stretch as the abdomen grew to accommodate her ovaries (from Arthropod exoskeleton)
Image 8This Zoea-stage larva is hardly recognisable as a crab, but each time it sheds its cuticle it remodels itself, eventually taking on its final crab form (from Arthropod exoskeleton)
Image 12Ghost crab, showing a variety of integument types in its exoskeleton, with transparent biomineralization over the eyes, strong biomineralization over the pincers, and tough chitin fabric in the joints and the bristles on the legs (from Arthropod exoskeleton)
Image 17Formation of anterior segments across arthropod taxa based on gene expression and neuroanatomical observations, Note the chelicera(Ch) and chelifore(Chf) arose from somite 1 and thus correspond to the first antenna(An/An1) of other arthropods. (from Chelicerata)
Image 21In honeypot antrepletes, the abdomens of the workers that hold the sugar solution grow vastly, but only the unsclerotised cuticle can stretch, leaving the unstretched sclerites as dark islands on the clear abdomen (from Arthropod exoskeleton)
Image 22Some of the various hypotheses of myriapod phylogeny. Morphological studies (trees a and b) support a sister grouping of Diplopoda and Pauropoda, while studies of DNA or amino acid similarities suggest a variety of different relationships, including the relationship of Pauropoda and Symphyla in tree c. (from Myriapoda)
Image 23Reconstruction of Mollisonia plenovenatrix, the oldest known arthropod with confirmed chelicerae (from Chelicerata)
Image 26The house centipedeScutigera coleoptrata has rigid sclerites on each body segment. Supple chitin holds the sclerites together and connects the segments flexibly. Similar chitin connects the joints in the legs. Sclerotised tubular leg segments house the leg muscles, their nerves and attachments, leaving room for the passage of blood to and from the hemocoel (from Arthropod exoskeleton)
Image 27 Honeybee larvae have flexible but delicate unsclerotised cuticles. (from Arthropod exoskeleton)
Image 32 This fully-grown robber crab has tough fabric forming its joints, delicate biomineralized cuticle over its sensory antennae, optic-quality over its eyes, and strong, calcite-reinforced chitin armouring its body and legs; its pincers can break into coconuts (from Arthropod exoskeleton)
Argiope trifasciata, the banded garden or banded orb-weaving spider, is a species of arachnid in the family Araneidae. It is native to North and South America but has spread to other parts of the world. This ventral view of a female A. trifasciata shows her in the centre of her web, which can reach a diameter of 60 cm (24 in). The function of the zig-zag web decorations is unclear, but they may serve to make the spider appear larger or to act as a warning sign.
Anthidium florentinum, a species of bee in the family Megachilidae. Bees are flying insects closely related to wasps and ants that are involved in pollination. There are nearly 20,000 known species of bees in seven recognized biological families. Bees are found on every continent except Antarctica, in every habitat on the planet that contains insect-pollinated flowering plants. Bees range in size from tiny stingless bee species whose workers are less than 2 millimetres (0.08 in) long, to Megachile pluto, whose females can attain a length of 39 millimetres (1.54 in).
The light blue soldier crab (Mictyris longicarpus) inhabits beaches in the Indo-Pacific region. Soldier crabs filter sand or mud for microorganisms. They congregate during the low tide, and bury themselves in a corkscrew pattern during high tide, or whenever they are threatened.
The red rock crab (Grapsus grapsus), also known as "Sally Lightfoot", is one of the commonest crabs along the western seaboard of the Americas. John Steinbeck wrote of them, "Everyone who has seen them has been delighted with them ... These little crabs, with brilliant cloisonné carapaces, walk on their tiptoes, they have remarkable eyes and an extremely fast reaction time." He tried to catch them but to little avail. "If you walk slowly, they move slowly ahead of you in droves. If you hurry, they hurry. When you plunge at them, they seem to disappear in a puff of blue smoke."
Attacus taprobanis is a species of moth in the family Saturniidae native to southern India and Sri Lanka. This adult male, photographed in Kadavoor, Kerala, developed from a larva feeding on a mahogany tree. When ready to pupate, the larva formed a papery cocoon 7.5 cm (3 in) long interwoven with a leaf; before doing this, the larva had attached the leaf to the stem with a silken thread and cut the leaf stalk. The colours of the dying leaf provided camouflage for the pupa, and the adult insect emerged some 24 days later.
Two Melangyna viridiceps (called Common Hoverflies in Australia) mating in mid-air. The male, which can be identified by the eyes meeting at the top of its head, is on top. The term "hoverfly" refers to about 6,000 species of flying insects in the family Syrphidae. They are often seen hovering at flowers and are important pollinators.
Compound eyes on a blue bottle fly. Unlike simple eyes, which have a single concave photoreceptive surface, compound eyes consist of a number of individual lenses (called ommatidia) laid out on a convex surface; this means that they point in slightly different directions. Compound eyes provide a wide field of view and can detect fast movement, but have low resolution.
The orb-weaver spiders (family Araneidae) are the familiar builders of spiral wheel-shaped webs often found in gardens, fields and forests. The family is a large one, including over 2800 species in over 160 genera worldwide, making it the third largest known (behind Salticidae and Linyphiidae). The web has always been thought of as an engineering marvel.
The western honey bee (Apis mellifera) is the most common of the 7–12 species of honey bee worldwide. It is believed to have originated in either Africa or Asia, and spread naturally through Africa, the Middle East and Europe. Following human introduction into the Americas and Oceania, the species is now found on every continent except Antarctica. Humans have been collecting honey from bees for thousands of years, with evidence in the form of rock art found in France and Spain, dating to around 7000 BC. Along with other insects, the honey bee is an important pollinator, with a large number of the crop species farmed worldwide depending on it.
A macro view of a Gonia capitatafly feeding on honey, showing its proboscis and pedipalps (the two appendages protruding from the proboscis), two types of insect mouthparts. The proboscis actually comprises the labium, a quadrupedal structure, and a sponge-like labellum at the end. Flies eat solid food by secreting saliva and dabbing it over the food item. As the saliva dissolves the food, the solution is then drawn up into the mouth as a liquid. The labellum's surface is covered by minute food channels which form a tube leading to the esophagus, and food is drawn up the channels by capillary action.
A Eusthenia species of stonefly. The order contains almost 3,500 known species, including the only known insects that are exclusively aquatic from birth to death. Stoneflies are believed to be one of the most primitive groups of Neoptera and are found worldwide, with the exception of Antarctica.
Purana tigrina is a species of cicada found in Southeast Asia. This adult male was photographed in Kadavoor, Kerala, in southern India, and is about one inch (25 mm) in length. The mouthparts are adapted to piercing plant tissues and sucking sap; the male abdomen houses the tymbal, an organ used in the production of song, while the female abdomen is tipped by a large, saw-edged ovipositor.
Xylotrupes socrates (Siamese rhinoceros beetle, or "fighting beetle"), male, on a banana leaf. This scarab beetle is particularly known for its role in insect fighting in Northern Laos and Thailand.
Squilla mantis, a species of mantis shrimp, for sale at the fish auction of l'Ametlla de Mar in Catalonia, Spain. It is native to the Mediterranean Sea and adjacent warm parts of the Atlantic Ocean, where it burrows into muddy and sandy seabeds. It is the only native stomatopod to be fished for on a commercial scale in the Mediterranean.
A nest of the tropical Asian giant honey bee, which consists of a single exposed honeycomb, an array of densely packed hexagonal cells made of beeswax. Honeycombs store food (honey and pollen) and house the "brood" (eggs, larvae, and pupae).
The Painted Lady (Vanessa cardui) is a well-known colourful butterfly, found on every continent except Antarctica. It occurs in any temperate zone, including mountains in the tropics. The species is resident only in warmer areas, but migrates in spring, and sometimes again in autumn.
Two flesh-flies (Sarcophaga ruficornis species pictured) mating. The life cycle of the saprophagic flesh-fly larvae has been well researched and is very predictable. Different species prefer bodies in different states of decomposition, which allows forensic entomologists to extrapolate the time of death.
The Ozyptila praticola species of crab spider is found throughout Europe and the Middle East. They do not build webs to trap prey, but are active hunters. Crab spiders are so named because of their first two pairs of legs, which are held out to the side giving them a crab-like appearance. Also, like crabs, these spiders move sideways and backwards more easily than forwards.
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