The Dictyoptera contain small, large, and medium sized insects, usually with two pairs of wings, the front pair being leathery and held over the hindwings. The name Dictyoptera is Greek meaning "diktyon" -net and "pteron"-wing. Insects in this order generally have long multi-segmented filiform antennae, biting mouthparts, tarsi comprising of five segments and conspicous cerci.

The origin of cockroaches dates back some 250 million years to the Carboniferous period, fossils of this time indicate that they were very numerous. It has been suggested that cockroaches were by far the most dominant winged insect at this time, outnumbering all other groups of winged insects together. The cockroach is probably best known for being completely unspecialised. It is used frequently in universities for teaching insect anatomy. The fossil record shows that they have changed little over the last 250 million years. The two features which have changed the most over this vast time period is (1) the female genitalia; the ovipositor having become so reduced that it is no longer visible externally and (2) the wings, with increased differentiation occuring between the back and front, and a total reduction in size of both pairs. Today the forewings (tegmina, forewings arising from the mesothoracic segment)of the more recently evolved cockroaches are used to cover and protect the hindwings. There are approximately 4000 species recognised today of which around 12 are associated with humans.

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cockroach

The earwigs are a well known group of insects even among non-entomologists. The Dermaptera is divided into three sub-orders, with nearly all species being within the sub-order Forficulina. The other two sub-orders are the Hemimerina, containing eleven species, and the Arixeniina which contains five species. The five species contained with the Arixeniina are unusual in that they have neither wings or the well developed cerci so characteristic of other species, and in the fact that they produce live young (nymphs) where all other species lay eggs. Both of these small sub-orders comprise of earwigs with specialized life-cycles, with Hemimerina species being ectoparasites on certain African rodents and Arixeniid species, also ectoparasites, on S.E. Asian bats which inhabit the caves at Hiah, Sarawak. The bats, (family Molossidae) roost in large numbers and the resident earwigs eg, Arixenia esua feed on body exudates and skin debris.

Earwigs are easily recognisable by the forcep-like terminal appendages (cerci) present on both sexes. The flexable abdomen is capable of bending up and over the insects body allowing an earwig to use its modified cerci for protection. Earwigs are generally a uniform brownish colour with the forewings being short and thickened, meeting along the mid-line of the body. The name earwig has possibly arisen from the belief that they will enter a persons ear and bite through the eardrum, a totally unfounded belief. Alternatively the name may have been derived from the ear shaped hindwings seen in many species, the name earwig steming from earwing. The sexes of most species are easy to differentiate as the cerci shape are dimorphic

The head carriers small to medium size compound eyes but no ocelli are present. The antennae are long and composed of many segments (as many as 50). Earwigs are nocturnal insects resting during the day in cracks and crevices which provide dark retreats. Their diet is omnivorous and they are also known to eat petals, frequently to the annoyance of horticulturalists. The hind wings of earwigs are often wonderfully shaped and show intricate veination. The actual name Dermaptera means skinwing (derma-skin, ptera-wing), a name derived from the delicate hindwings which resemble human skin, such as that which is shed after getting sun-burnt. The elytra of an earwig are only small and so in order to house the wings they are greatly folded resulting in up to forty or so layers on top of each other.

Earwigs are unusual in their reproductive biology by the fact that females show a degree of maternal care for their offspring. Forficula auricularia, a common earwig in the UK will lay between 20 and 50 eggs within a small cavity in the soil and care for them through the harsh winter months. She will clean them to prevent fungal attacks and defend them from predators until they are ready to hatch in the spring. The first instar nymphs are fed by their mother and they come above ground at the second instar stage, where they are still fed by the mother until they are able to feed and care for themselves.

These insects are small to medium sized insects, (usually under 12mm but can be up to 20) which live under an intricate web of silken tunnels which are woven on tree trunks, in leaf litter or in the soil. Females are wingless but the males are capable of flight, having two pairs of wings of equal size which can be inflated with haemolymph to enable flight. The insects live in colonies under their protective silk and feed on lichens and other plant material. Males however can have mouthparts which differ considerably from that of females and so their diet may include other small invertebrates. The silk glands are situated within the tarsi of the forelegs which are swollen in order to accomadate these glands. The insects are long and cylindrical, have small eyes with antennae comprising of between ten and thirty-five segments. Distribution of web-spinners is generally confined to tropical regions, although they can be found in some of the warmer temperate areas. Females lay eggs around June and by August it is not unusual to see first instar nymphs. Classification is based upon wing veination and in the males the genitalia. Male genitalia is often prominant and may be asymmetrical. The web-spinners are seperated into eight families.

These insects are often seen flying over rivers in the summer months in huge numbers. They have wonderful densely veined wings, long legs and are quite delicate in appearance. They have very long cerci and frequently a middle terminal extention between the two cerci. The two pairs of wings are of unequal size. The hind wings, which in some species may be absent, are considerably smaller than the fore wings. The wings are held in a similar fashion to that seen in butterflies, together and upright over the thorax and abdomen. Classification is mainly based on wing veination. The name Ephemeroptera means - ephemeros: living a day, and pteron: wing. There are nineteen families in total.

Mayflies are the oldest of the winged insects and are unique in being the only known insect group which has a sub-imago stage. This is a pre-adult stage which undergoes a final moult even though it has fully functional wings. The sub-imago stage is also called a "dun", whilst the imago is reffered to as a "spinner", being brighter and shinier than the sub-imago. Mayflies are associated with an aquatic environment, with the nymphal stages living in rivers and streams, and the adults which are found flying along waterways. The adult stage of mayflies is extremely short, often lasting for only a day, or even only a few hours. Adults have no functional mouthparts and there only purpose is to mate, which takes place on the wing after which the females may lay eggs in less than an hour. Their purpose fulfilled they quickly die. Eggs are laid in a variety of ways by females. Some scatter eggs singularly along streams and rivers, other lay their eggs in batches, whilst others actually crawl under the water surface, using emergent vegetation and lay their eggs directly onto water plants.

Nymphs vary in morphology according to the life strategy they use within the water. Nymphs either burrow in the river bed, these being cylindrical in shape. Crawl on vegetation, these nymphs are usually sturdy with strong legs and tarsi to obtain good purchase against the current. Some nymphs swim and are therefore very streamlined to aid passage through the water. Others live in the fast currents feeding on algae films and detritus which passes in the current. These nymphs are dorso-ventrally flattened and capable of clinging to rock surfaces against considerable forces of drag. Nymphs breathe using a series of gill filiments which can easily be seen extending from the sides of the abdomen. The gills are flat leaf like organs and house numerous tracheae into which oxygen from the water diffuses. There are usually seven pairs of gills and the nymph will often flick them periodically if placed in still water, this removes the oxygen deficient water immediately next to the gills and replaces it with more oxygen rich water. The nymphal stages are considerably longer than the adult stage. Ephemera danica takes two years to mature to the short lived adult stage. Some nymphs moult over twenty five times before becoming adults.

The rock crawlers are a small group of insects occuring only within the Northern hemisphere. They are hemimetabolous insects with around twenty species known at present. They are found in extremely cold climates, in Japan, Siberia and Northern America. Adults are between 12 and 25mm in length, slender in shape with no wings. The head may house small compound eyes, although in some species eyes are not present. The mouthparts are simple and of the biting type, with mosses and other vegetation being the main diet, although other insects may also be eaten. There are two cerci on the last abdominal segment and an ovipositor is also present in females. They are not a widely studied group and hence little is known of the biology and lifecycle of any species.

The Hemiptera is a large group of insects which is often sub-divided into the (Stictocephala bisonia) Heteroptera and the Homoptera. The name hemiptera means, hemi-half, and pteron-wing. Such a name arises from the morphology of the forewings. In an heteropteran bug the wings, (if present-wings are absent in some species), have two regions, a hard leathery basal area, and a delicate membranous distal area. The position of the wings at rest are also different between the two sub-orders, heteropterans hold their wings flat over the abdomen, whilst homopterans form a pitched roof type structure with their wings. The name heteros means different (referring to the basal and distal parts of the wing), and homos means the same (all the wing is membranous).

Although commonly called white ants termites form a completely seperate order and are not closely related to ants. They have developed a similar social organization to the ants and bees. They are actually related to the cochroaches. The name isoptera means isos-equal and pteron-wing. The wings when produced (most termites do not have wings) have two pairs with simple veination, they are used for a short period during mating and are quickly broken off from the thorax, an act that is facilitated by a basal fracture line on the wings.

The social structure of these insects is divided into groups of termites within the colony that have different morphologies according to their role. These different types or forms are called castes; workers, soldiers and reproductives. Workers are soft-bodied, wingless with small antennae. Soldiers often have large heads which are modified to bite, pierce or cut potential invaders to the colony. Colonies can range in size from a few hundred to many millions. The mounds which are built by termites can be many meters high and are maintained at a constant temperature and humidity internally by the complex architecture of the nest. Many species do not build elaborate nests but live within rotten wood and other vegetable matter. Due to the high cellose content of their diet termites harbour symbiotic bacteria and protozoans within their guts to help them digest this tough material. There are seven families and around 2,300 species.

Termites are predominantly tropical insects with only two species found in Europe. The cuticle of the thorax and abdomen is soft and pale in colour in termites, with only the head capsule being formed from hard cuticle. Eyes are reduced or absent in the worker and soldier castes, whilst compound eyes are seen in the reproductives. Termites are often classified and identified by the shape of the pronotum which is distinct from the rest of the thorax. All termite castes have a short pair of cerci. The important difference in social structure between termites and ants is that termites have all castes represented by roughly equal numbers of both sexes. The reproductives of some species have been reported to live for up to fifty years.

Mallophaga - biting lice - are probably better thought of as chewing lice as they are not blood feeders. They feed on dead skin and fragments of hair or feathers. They are found on mammals and birds although the majority are found on birds. Eyes in Mallophaga are either absent or very reduced and the mandibles are developed for chewing. The order is divided into the suborders Amblycera and Ischnocera. The Amblycera are generally considered to be more primitive with hosts including birds, marsupials and mammals. Bird lice are characterized by having two tarsal claws on each leg whilst only one tarsal claw is present on lice of mammals. Amblycera feed on skin debris primarily although blood feeding may occur due to the rasping action of the mandibles.

Ischnocera are usually referred to as feather or hair lice as they are adapted to cling onto these structures rather than the skin. Their diet consists of mostly keratin and in order for digestion to occur gut symbionts or specific enzymes are present. Eggs of both suborders are laid singularly and glued to the hosts hair or feathers. They are laid close to the skin as a higher temperature is maintained here. Eggs usually develop in approximately one to two weeks. Total development time from egg to adult therefore takes from three to five weeks. Adult lifespan has been reported to vary from one month to several months.

The stoneflies are a small order of moderate to large sized insects with aquatic nymphs. The adult forms are poor fliers and seldom venture far from their larval habitat of lakes, streams and rivers. The name of the order is derived from the Greek word - plectos: pleated; and pteron meaning wing. There are fifteen families wth approximately 1,600 species.The larvae are usually found inhabiting well aerated water courses, attached to stones and rocks. A few species are known to occur in slow lotic waters and they do not tolerate polluted water and so act as indicators of water quality. In the imagos the antennae are long and setaceous, comprised of numerous segments, there are a pair of well developed compound eyes, situated between which are usually three, although sometimes two ocelli. The mouthparts are frequently weakly developed. Some of the features exhibited by stoneflies are primitive and this is particularly seen in the composition of the thorax. The prothorax is large and mobile and the pleuron shows no differentiation into episternum and epimeron. The mesothorax and the metathorax are shown to exhibit the usual features of prescutum, scutum, scutellum and postnotum dorsally, with the episternum and epimeron divisions pleurally. There are two pairs of membranous wings, with the hind wings always being considerably larger than the forewings. Some families have a coupling mechanisms for the wings but the majority do not. One unusual aspect of the wing veination is frequent asymmetry within individuals showing great variation of the subordinate veins. There are only a few apterous forms within this order although there are sexually dimorphic species where one sex has reduced wing size e.g. Dinocras cephalotes. Females show no ovipositor and the abdomen has ten developed segments and reminants of the eleventh.

Mating occurs on the ground ( at least not in the air ) and according to family the eggs may be either already developed at the time of mating or take several weeks to develop after mating occurs. Stoneflies in general lay large numbers of eggs, Pteronarcys proteus for example lays between 500 - 1000 in batches of 150 over a period of two or three weeks. The eggs are oviposited contained within a gelatinous mass which subsequently dissolves on contact with the water leaving the eggs to become individual within the water course. In most species the females oviposit by dipping their abdomen under the water surface whilst in flight, a few species will actually crawl on stones and plants by the waters edge, or over the water surface to oviposit, this behaviour is seen in the larger Perlidae. Reports of more unusual behaviour during oviposition include females of Allocapnia crawling into the water to lay their eggs and that Leuctra females carry their eggs on the back of their abdomen before positioning them at a suitable site. The lifecycle is a hemimetabolous one with nymphs showing a quite high degree of similarity to the adult forms. The nymphs are recognised by two main diagonistic characters, the long multi-articulate antennae and their two long cerci. The legs of the nymphs are long and fringed laterally with setae, each leg terminates with a paired claw. Gills may or may not be apparent, the primitive nymphs belonging to the Eustheniidae has five or six paired gills running laterally along the abdomen, whilst Leuctra, Capnia and Isoperla have no gills or visible respiratory appendages. Nymphs exhibit a variety of feeding habits from predators ( seen especially in Perlid) to herbivorous and polyphagous, such diet variation is shown clearly in the structure of mouthparts between the feeding types. Development time as with most insects is greatly effected by temperature and size. Small forms can develop within a year whilst larger forms in colder climates can take three to four years to complete their life cycle. Number of instars varies greatly between species but not, apparently, within species. The number of instars has been reported from 12 in Pteronarcys proteus ( over two years) to 33 in Dinocras cephalotes (over a three year period).

About 2500 species are known with the largest number occurring the oriental region. The order is divided into two families the Phylliidae, which generally contains the leaf type insets, and the Phasmatidae, which contains the stick like insects. These predominantly tropical insects exhibit remarkable adaptations allowing them to be extremely cryptic within vegetation, giving rise to their common names of leaf and stick insects. The majority are cylindrical, elongate large insects varying in colour from shades of green to brown. Some species have evolved to become dorso-ventrally flattened and have extentions of the legs and body to mimic the leaf of their host plant. The antennae can vary considerable between species from 8 segments to over a hundred. There are both winged and apterous species although all species have compound eyes. Ocelli are usually lacking in apterous forms. The mandibles are well developed and all species are phytophagous. Winged forms are known if some what rare. The forewings are reduced in size forming tegmina and are subsequently sclerotized, the hind wings of the leaf insects often imitate leaf veins. Legs of phasmida can ofetn be regrown quickly if lost during ecdysis or other mishap, the new limb will only have four tarsal segments rather than the usual five however.

Mating may last for many hours in some species and the female will lay many single eggs which are dropped to the ground beneath the host plant. The eggs are small and operculate with a thick shell. The hatching time of the egg can be many months after oviposition. In Phyllium bioculatum there is six instars in the females cycle and only four in the males, the males are also shorter lived than the females, which live for about 90 days in which time they lay around 100 eggs. An interesting fact of some species is that they are either partly or totally parthenogenetic. In some species males are uncommon and infrequently seen with a population, eggs from unfertilized females give rise to females only. Other species are exclusively parthenogenetic, such as Bacillus, Clonopsis and Carausius. Some species also have the ability to change colour to match or blend better with the back ground. This is done by the movement of pigment granules within epidermal cells.