The class Insecta (insects) is split into two sub classes and twenty – four orders. Here, a very concise outline of the main diagnostic features of each order is given together with some common examples.
Sub – Class Apterygota
The orders in this sub – class consist of wingless insects, the condition being primitive. They are the Diplura, Thysanura, Collembola and Protura. None undergo metamorphosis.
Order 1: Diplura
Very small white insects with no eyes. Found in soil and under stones. Long antennae and anal cerci. Almost “living fossils”, they are survivors of a very ancient group (e.g., Campodea). All the Diplura were formerly included in the Thysanura and were known as the two pronged bristle tails.
Order 2: Thysanura
The well – known silver – fish and sugar – brats. The antennae are long and there is a median appendage on the last segment as well as the two long anal cerci. The body is covered with scales (e.g., Lepisma Saccharina, the silver – fish)
Order 3: Collembola
Very small insects with short antennae and a forked springing organ on the fourth abdominal segment. They have no compound eyes. The abdomen is peculiar in possessing only six segments. They are extremely common in the soil, on pasture land and in decaying organic matter (e.g., the spring – tails).
Order 4: Protura
Minute insects with twelve segments in the abdomen. No antennae or compound eyes or cerci, very small legs. Found under the bark of trees, in turf and in soil. Size about 1mm or less.
Sub – Class Pterygota
This sub – class contains the remaining twenty orders. All either bear wings or are secondarily wingless. There is a metamorphosis which may be complete or incomplete.
Order 5: Orthoptera
The characteristics of the order have been given. It includes cockroaches, crickets, grass – hoppers, locusts, stick insects, praying insects.
Order 6: Plecoptera
Long slender antennae and anal cerci. Mouth parts are reduced and weak. Always found near water: the nymphs are aquatic (e.g., the stone – flies).
Order 7: Dermaptera
Cerci modified to form forceps. Front – – wings reduced to small leathery tegmina. Slight metamorphosis (E.g., the earwings).
Order 8: Embioptera
Mainly tropical and sub – tropical. They spin silken tunnels in which they live. Both pairs of wings alike and oftwn absent in the females. Elongated antennae. slight metamorphosis in the male: none in the female (e.g., the web – spinners) none are British.
Order 9: Isoptera
Social insects living in large communities. Reproductive castes and sterile castes; king, queen, soldiers and workers. Fully winged, partly winged and non – winged forms. Wings both similar and can be shed. Mouth parts biting. Metamorphosis slight or incomplete. Mainly tropical and subtropical (e.g., the termites or “white ants”).
Order 10: Ephemeroptera
Short – lived imagines; aquatic nymphs. Mouth parts atrophied or almost so. Very long cerci and a median caudal filament. Long antennae. hindwings much reduced (e.g., the May – flies).
Order 11: Odonata
Long bodied, brilliant metallic colors. Mouth parts biting. Wings equal. Very large eyes. Aquatic nymphs (e.g., the dragonflies).
Order 12: Psocoptera
Very small insects. Winged with anterior wings larger or wingless. Cerci atrophied or almost so. Antennae fairly long. Biting mouth parts. Metamorphosis little or absent (e.g., book – lice and their allies).
Order 13: Anoplura
All ectoparasites of birds and animals. Wingless. Mouth parts for biting or piercing. Lattened body, short legs with claws adapted for clinging. No cerci. Biting and sucking lice. Notorious carriers of disease.
Order 14: Thysanoptera
Very small insects with short antennae. piercing and sucking mouth parts. Wings narrow and fringed with long setae. No cerci. The thrips insects do great damage to plants by sucking the sap. Pea – thrips, corn – thrips, pear thrips, etc.
Order 15: Hemiptera
Small insects with piercing and sucking mouth parts. Often wingless parthenogenetic generations. No cerci. Usually gradual metamorphosis. The plant bugs. Aphides, scale insects, mealy bugs, leaf – hoppers, the “musical” cicadas, the greenhouse white – fly. Many are carriers of virus diseases.
Order 16: Neuroptera
Medium soft – bodied insects with long antennae. being mouth parts. No cerci. Many have aquatic larvae. Alder flies, snake flies, lace – wings, ant lions.
Order 17: Mecoptera
Small insects with biting mouth parts. Long antennae. wings similar. Cerci reduced. Conspicuous bands or spots on the wings. The scorpion flies.
Order 18: Trichoptera
Medium insects of weak flight, often resembling moths. Mouth parts adapted for licking but many imagines do not feed. Antennae and cerci of medium length. Aquatic larvae, the caddis – worms, which make remarkable cases for concealment and protection
Order 19: Lepidoptera
Small to large insects with entire covering of powdery scales. Wings fastened together. Sucking proboscis formed by maxille. No cerci. Metamorphosis is complete. The butterflies and moths.
Order 20: Coleoptera
Size ranges from minute to large. Force – wings always horny elytra. Mouth parts biting. Metamorphosis complete. The beetles.
Order 21: Strepsiptera
Small insects; larvae parasites in other insects, especially Hymenoptera. Antennae bifid, mouth parts biting, but often degenerate. Fore – wings are halters, hind – wings fan – shaped. No cerci. Stylops, a British genus, has sixteen endemic species.
Order 22: Hymenoptera
Small to medium insects, many of them social. Metamorphosis complete. Antennae short. Mouth parts very midified for biting or sucking. Often castes present: queens, drones, workers, soldiers. Parthenogenesis is common. The saw – flies, ichneumon flies, chalcids, gall – wasps, ants, wasps, bees, hornets.
Order 23: Diptera
Hind – wings form halters. Antennae various but usually short. Mouth parts suctorial, often piercing also. Cerci very reduced or absent. Metamorphosis complete. Larvae are apodous. The true two – winged flies. Many are important as vectors of disease; the housefly, mosquito, teste fly: crane – flies, midges, horse – flies, hover – flies, warble – flies.
Order 24: Aphaniptera
Small insects, all ectoparasitic. Body laterally flattened. Short antennae. mouth parts for piercing and sucking. Legs adapted for jumping. No cerci. No wings.