From the embryonic stages, a layer of columnar or cuboidal epithelial cells gives rise to the external cuticle and an internal basement membrane. Insects are also used as environmental quality indicators to assess water quality and soil contamination and are the basis of many studies of biodiversity. 2.7 Types of body segmentation. [38], At the posterior angle of the wing base in some Diptera, there is a pair of membranous lobes (squamae, or calypteres) known as the alula. The clypeogenal suture laterally demarcates the clypeus, with the clypeus ventrally separated from the labrum by the clypeolabral suture. As digestion slowly occurs, lipids are synthesized and accumulate in the fat body, mainly as triacylglycerol, in . Of all the insect orders, Orthoptera displays the greatest variety of features found in the heads of insects, including the sutures and sclerites. Corrections? [38]:163164, The inflection of the coxal wall bearing the pleural articular surface divides the lateral wall of the basicoxite into a prearticular part and a postarticular part, and the two areas often appear as two marginal lobes on the base of the coxa. In females there are three types of genitalia based on the relating taxa: monotrysian, exoporian, and dytresian. The tarsus is occasionally fused with the tibia in larval insects, forming a tibiotarsal segment; in some cases, it appears to be eliminated or reduced to a rudiment between the tibia and the pretarsus. Smith, John Bernhard, Explanation of terms used in entomology Publisher: Brooklyn entomological society 1906 (May be downloaded from: CS1 maint: multiple names: authors list (, https://archive.org/details/explanationofter00smit, "Optics and phylogeny: is there an insight? The postgena is the area immediately posteriad, or posterior or lower on the gena of pterygote insects, and forms the lateral and ventral parts of the occipital arch. [38]:164, The trochanter is the basal segment of the telopodite; it is always a small segment in the insect leg, freely movable by a horizontal hinge on the coxa, but more or less fixed to the base of the femur. In prognathous insects, the vertex is not found between the compound eyes, but rather where the ocelli are normally found. The ecdysial suture is longitudinally placed on the vertex, separating the epicranial halves of the head to the left and right sides. [12] [30] The muscles of the cibarium or pharynx are strongly developed and form the pump. In nymphal wings, its trachea arises between the cubital trachea and the group of vannal tracheae. This type of eye gives less resolution than eyes found in vertebrates, but it gives an acute perception of movement and usually possesses UV- and green sensitivity, and may have additional sensitivity peaks in other regions of the visual spectrum. To see with a resolution comparable to our simple eyes, humans would require compound eyes that would each reach the size of their heads. The number of Malpighian tubules possessed by a given insect varies between species, ranging from only two tubules in some insects to over 100 tubules in others. The rectum absorbs 90% of the water in these fecal pellets, and the dry pellet is then eliminated through the anus (element 17), completing the process of digestion. The seminal vesicles have glandular linings that secrete nutrients for nourishment and maintenance of the sperm. As the salivary glands produce fluid and carbohydrate-digesting enzymes (mostly amylases), strong muscles in the pharynx pump fluid into the buccal cavity, lubricating the food like the salivarium does, and helping blood feeders, and xylem and phloem feeders. The phylum also includes spiders, centipedes, and crustaceans. Since all winged insects are believed to have evolved from a common ancestor, the archediction represents the "template" that has been modified (and streamlined) by natural selection for 200 million years. By moving its mouthparts (element 32 in numbered diagram) the insect can mix its food with saliva. The tibia is characteristically a slender segment in adult insects, only a little shorter than the femur or the combined femur and trochanter. This is chitinous and much thicker than the epicuticle and has two layers, the outer is the exocuticle while the inner is the endocuticle. Many species of insects have reduced numbers of ganglia due to fusion or reduction. In its pure form, it is leathery, but when encrusted in calcium carbonate, it becomes much harder. Updates? The posterior portion of the remigium is sometimes called the clavus; the two other posterior fields are the anal and jugal areas. Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. We've seen that arthropods all have bilateral symmetry, segmented bodies, and hard exoskeletons. The second axillary sclerite (2Ax) is more variable in form than the first axillary, but its mechanical relations are no less definite. In the cicada, the vannal fold lies immediately behind the first vannal vein (lV). [27] Most of the hypopharynx is membranous, but the adoral face is sclerotized distally, and proximally contains a pair of suspensory sclerites extending upwards to end in the lateral wall of the stomodeum. The subgenal area is usually narrow, located above the mouthparts; this area also includes the hypostoma and pleurostoma. The foregut includes the buccal cavity (mouth), pharynx, esophagus, and Crop and proventriculus (any part may be highly modified), which both store food and signify when to continue passing onward to the midgut. Insect respiration is accomplished without lungs. The thoracic segments have one ganglion on each side, which are connected into a pair, one pair per segment. Though fold lines may be transverse, as in the hindwings of beetles and earwigs, they are normally radial to the base of the wing, allowing adjacent sections of a wing to be folded over or under each other. The basal shafts of the veins are convex, but each vein forks distally into an anterior convex branch and a posterior concave branch. It is then emptied directly into the alimentary canal, at the junction between the midgut and hindgut. The larvae of Cyclorrhapha however, tend to have hardly any head capsule at all. [1]:2224 These muscles can contract multiple times for each single nerve impulse, allowing the wings to beat faster than would ordinarily be possible. Paternity testing of insects has revealed that some, and probably many, female insects use the spermatheca and various ducts to control or bias sperm used in favor of some males over others. The pterothoracic nota each have two main divisions: the anterior, wing-bearing alinotum and the posterior, phragma-bearing postnotum. [8]:15, Most insects have one pair of large, prominent compound eyes composed of units called ommatidia (ommatidium, singular), up to 30,000 in a single compound eye of, for example, large dragonflies. Each segment has four basic regions. In species of Lepidoptera, it consists of two tubes held together by hooks and separable for cleaning. Three physical features separate insects from other arthropods: they have a body divided into three regions (called tagmata) (head, thorax, and abdomen), three pairs of legs, and mouthparts located outside of the head capsule. The mandibles are positioned between the labrum and maxillae. The labrum is a broad lobe forming the roof of the preoral cavity, suspended from the clypeus in front of the mouth and forming the upper lip. In Brachycera, the labellum is especially prominent and used for sponging liquid or semiliquid food. The base of the aedeagus may be the partially sclerotized phallotheca, also called the phallosoma or theca. Ordinarily, however, a definite number of cross-veins having specific locations occurs. They dominate the present-day land fauna with about 1 million described species. Terga are separated from each other and from the adjacent sterna or pleura by a membrane. Long, slender (extratory) malpighian tubules can be found between the junction of the mid- and hind gut. However, apterygotes (bristletails and silverfish) and many immature aquatic insects have abdominal appendages. Omissions? The light produce is highly efficient, as it is produced by oxidation of luciferin by the enzymes luciferase in the presence of ATP (adenosine triphosphate) and oxygen, producing oxyluciferin, carbon dioxide, and light. Its anterior part is supported on the anterior notal wing process of the tergum (ANP); its posterior part articulates with the tergal margin. The sclerite anterior to the pleural suture is called the episternum (serially, the mesepisternum and metepisternum). [31] The proboscis is coiled under the head when the insect is at rest and is extended only when feeding. [46], An insect uses its digestive system for all steps in food processing: digestion, absorption, and feces delivery and elimination. Continuing with this logic, there are also the mesopleura and metapleura, as well as the mesosternum and metasternum. [24], The mouthparts and rest of the head can be articulated in at least three different positions: prognathous, opisthognathous, and hypognathous. The following diagrams outline common characteristics found in insect anatomy, including detailed parts of wings, legs, and head. Arthropods are members of the taxonomic phylum Arthropoda, which includes insects, arachnids, and crustaceans. [17]:811 However, touch is not the only thing that antennae can detect; numerous tiny sensory structures on the antennae allow insects to sense smells, temperature, humidity, pressure, and even potentially sense themselves in space. Toward the middle of the wing, it forks into a first undivided branch (R1) and a second branch, called the radial sector (Ra), which subdivides dichotomously into four distal branches (R2, R3, R4, R5). In some insects, the coxal suture falls in line with the pleural suture. Spiders have a combination of head and thorax (cephalothorax) and abdomen. [8], The neuroendocrine system is typical of insects. With three thoracic and seven or eight abdominal ganglia can be distinguished to that in which all the thoracic and abdominal ganglia are fused to form a composite structure. In reproductive system of butterflies and moths, the male genitalia are complex and unclear. Compared with simple eyes, compound eyes possess very large view angles and better acuity than the insect's dorsal ocelli, but some stemmatal (= larval eyes), for example, those of sawfly larvae (Tenthredinidae) with an acuity of 4 degrees and very high polarization sensitivity, match the performance of compound eyes. [2] The head is specialized for sensory input and food intake; the thorax, which is the anchor point for the legs and wings (if present), is specialized for locomotion; and the abdomen is for digestion, respiration, excretion, and reproduction. Maxillae can have hairs and "teeth" along their inner margins. The scales of Lepidoptera and Trichoptera are highly modified macrotrichia. In adult insects, it is commonly subdivided into two to five subsegments, or tarsomeres, but in the Protura, some Collembola, and most holometabolous insect larvae it preserves the primitive form of a simple segment. There is enormous variation in body structure amongst insect species. Their reproductive systems are made up of a pair of ovaries, accessory glands, one or more spermathecae, and ducts connecting these parts. At the outer margin, the galea is a cupped or scoop-like structure, which sits over the outer edge of the labium. The base of the triangle (a-b) is the hinge of the wing with the body; the apex (c) is the distal end of the third axillary sclerite; the longer side is anterior to the apex. Distally, the vannal veins are either simple or branched. The remaining antennal segments or flagellomeres are called the flagellum. These vesicles are derived from the coxal and trochanteral endites (inner annulated lobes) of the ancestral abdominal appendages. Basic Insect Morphology. Making up usually less than 25% of an insect's body weight, it transports hormones, nutrients and wastes and has a role in, osmoregulation, temperature control, immunity, storage (water, carbohydrates and fats) and skeletal function. Among social insects, queen termites may live for up to 50 years, whereas some adult mayflies live less than two hours. The proximal part of the maxilla consists of a basal cardo, which has a single articulation with the head, and a flat plate, the stipes, hinged to the cardo. The vas deferens is sometimes drawn into (folded into) the phallotheca together with a seminal vesicle. [1]:70 Here, digestion starts as partially chewed food is broken down by saliva from the salivary glands. The open circulatory system of the beetle is driven by a tube-like heart attached to the top inside of the thorax. Please refer to the appropriate style manual or other sources if you have any questions. [58] Movement of haemolymph is particularly important for thermoregulation in orders such as Odonata, Lepidoptera, Hymenoptera and Diptera.[1]. The membrane is formed by two layers of integument closely apposed, while the veins are formed where the two layers remain separate and the cuticle may be thicker and more heavily sclerotized. [8], A notable number of species have developed special glands that produce chemicals for deterring predators (see Defense and predation). [1]:2224 The cutting edges are typically strengthened by the addition of zinc, manganese, or rarely, iron, in amounts up to about 4% of the dry weight. In numbers of species and individuals and in adaptability and wide distribution, insects are perhaps the most eminently successful group of all animals. Corrections? In some insects, the role of the microvilli and where they are located may vary. The sclerite posterior to the suture is called the epimiron (serially, the mesepimiron and metepimiron). [38], The various movements of the wings, especially in insects that flex their wings horizontally over their backs when at rest, demand a more complicated articular structure at the wing base than a mere hinge of the wing with the body. The meron reaches the extreme of its departure from the usual condition in the Diptera. The fourth axillary sclerite is not a constant element of the wing base. The forewing, which goes by different names in different orders (e.g., the tegmina in Orthoptera and elytra in Coleoptera), arises between the mesonotum and the mesopleuron, and the hindwing articulates between the metanotum and metapleuron. The gland is made of two containing chambers. In its unmodified form, chitin is translucent, pliable, and resilient. The arthropod body consists of three segments with a hard exoskeleton and jointed appendages. [1]:49 The small segment 11 may be represented by an epiproct (usually a dorsal plate or filament above the anus of certain insects); other appendages include: The nervous system of an insect can be divided into a brain and a ventral nerve cord. The alula is well developed in the house fly. It is closed against the mandibles in part by two muscles arising in the head and inserted on the posterior lateral margins on two small sclerites, the tormae, and, at least in some insects, by a resilin spring in the cuticle at the junction of the labrum with the clypeus. An esophagus follows and leads to the posterior of the pharynx and in some species forms a form of crop. The zoological categories of genetics, taxonomy, morphology, physiology, behaviour, and ecology are included in this field of study. The articular sclerites, or pteralia, of the wing base of the wing-flexing insects and their relations to the body and the wing veins, shown diagrammatically, are as follows: The humeral plate is usually a small sclerite on the anterior margin of the wing base, movable and articulated with the base of the costal vein. According to current dogma, the archedictyon contained six to eight longitudinal veins. [65] All species studied so far carry the obligate mutualistic endosymbiont bacterium Blattabacterium, with the exception of Nocticola australiensis, an Australian cave dwelling species without eyes, pigment or wings, and which recent genetic studies indicates are very primitive cockroaches. Insect | Definition, Characteristics, Types, Beneficial, Pest The insect body is divided into three main parts, the head, thorax and abdomen. The third axillary, therefore, is usually the posterior hinge plate of the wing base and is the active sclerite of the flexor mechanism, which directly manipulates the vannal veins. The most common coupling mechanism (e.g., Hymenoptera and Trichoptera) is a row of small hooks on the forward margin of the hindwing, or "hamuli", which lock onto the forewing, keeping them held together (hamulate coupling). Even though beetles constitute a large order and live in a variety of niches, examples of hearing is surprisingly lacking in species, though it is likely that most are just undiscovered. An "arthropod" is an invertebrate animal that has an exoskeleton, a segmented body, and jointed appendages. Then, through the hypopharynx, the mosquito injects saliva, which contains anticoagulants to stop the blood from clotting. Posteriorly, the articular membrane often forms an ample lobe between the wing and the body, and its margin is generally thickened and corrugated, giving the appearance of a ligament, the so-called axillary cord, continuous mesally with the posterior marginal scutellar fold of the tergal plate bearing the wing.[38]. Proximally, the main stem of the cubitus is associated with the distal median plate (m') of the wing base. Most butterflies and moths display the usual digestive cycle, however species that have a different diet require adaptations to meet these new demands. [26]:45, The ground plan of the abdomen of an adult insect typically consists of 1112 segments and is less strongly sclerotized than the head or thorax. However, since it cannot grow, the external sclerotized part of the cuticle is periodically shed in a process called "molting". [1]:49 Of the rest of the abdominal segments consist of the reproductive and anal parts. Folding is produced by a muscle arising on the pleuron and inserted into the third axillary sclerite in such a way that when it contracts, the sclerite pivots about its points of articulation with the posterior notal process and the second axillary sclerite. Since oxygen is delivered directly, the circulatory system is not used to carry oxygen, and is therefore greatly reduced. If there is a median ocellus, it generally is on the frons, though in some insects such as many Hymenoptera, all three ocelli appear on the vertex. Microscopic projections from the midgut wall, called microvilli, increase the surface area of the wall and allow more nutrients to be absorbed; they tend to be close to the origin of the midgut. As you may remember from elementary school, the most basic definition of an insect is an organism with three pairs of legs and three body regions: head, thorax, and abdomen. Haustellate mouthparts are used for sucking liquids and can be further classified by the presence of stylets, which include piercing-sucking, sponging, and siphoning. The vannal region is usually best developed in the hindwing, in which it may be enlarged to form a sustaining surface, as in Plecoptera and Orthoptera. This leads to flies having more reproduction abilities than most insects and at a much quicker rate. [30] There is an allometric scaling relationship between the body mass of Lepidoptera and length of the proboscis[33] from which an interesting adaptive departure is the unusually long-tongued hawk moth Xanthopan morganii praedicta. Wing folding can be very complicated, with transverse folding occurring in the hindwings of Dermaptera and Coleoptera, and in some insects, the anal area can be folded like a fan. [8]:13. Like other insect species, beetles have hemolymph instead of blood. In the archetype pattern (A), the media forks into two main branches, a media anterior (MA), which divides into two distal branches (MA1, MA2), and a median sector, or media posterior (MP), which has four terminal branches (M1, M2, M3, M4). The body of the sclerite articulates laterally with the second axillary. The energy stored in fatty acids is essential for several critical activities of insects, such as embryogenesis, oviposition, and flight. For example, gressorial and cursorial, or walking and running type insects respectively, usually have well-developed femora and tibiae on all legs, whereas jumping (saltatorial) insects such as grasshoppers have disproportionately developed metafemora and metatibiae. The evolution of superposition eyes in the Decapoda (Crustacea)", "Allometry and functional constraints on proboscis lengths in butterflies", "A New Method of Studying the Wing Veins of the Mayflies and Some Results Therefrom (Ephemerida)", Amateur Entomologist's Society: epiproct definition, "Discontinuous respiration in insects: role of the spiracles", "painless, a Drosophila gene essential for nociception", "General Entomology Digestive and Excritory system", Revisiting the formation of midgut epithelium in Zygentoma (Insecta) from a developmental study of the firebrat Thermobia domestica (Packard, 1873) (Lepismatidae), "Evidence for Cocladogenesis Between Diverse Dictyopteran Lineages and Their Intracellular Endosymbionts", "Physiology of insect diapause. A segmented bodymuch like a worm but with special groups of segments called "tagmata" Paired segmented appendages (legs) Bilateral symmetry (the right and left half look the same) An external skeleton that is molted as the animal grows What makes insects different than spiders, crabs and scorpions? In larvae, long-necked and stalked goblet cells are found in the anterior and posterior midgut regions, respectively. The following families of organisms are all examples of arthropods: Insects such as ants, dragonflies, and bees Arachnids such as spiders and scorpions Myriapods (a term which means "many feet") such as centipedes and milipedes [34], The mouthparts of insects that feed on fluids are modified in various ways to form a tube through which liquid can be drawn into the mouth and usually another through which saliva passes. The pleural articular surface of the coxa is borne on a mesal inflection of the coxal wall. The gut is where almost all of insects' digestion takes place.