(This Also Includes Non-Insect Hexapods)
In simplified taxonomy, the classification “Order” is preceded by Class (Insecta), Phylum (Arthropoda) and Kingdom (Animalia). This Part One1 deals with the hemimetabolous (or “heterometabolous”) insect orders, as they do not undergo complete metamorphosis to reach adulthood. Instead, their young (“nymphs”) look like miniature adults. The following entries and classifications will be based the fifth edition of Gullan & Cranston’s, “the Insects”, with additional tangents (like, “why don’t bats get lice?”) added by Yours Truly.
All insects are six-legged animals, but not all six-legged animals are insects, for there are also primitive, soil-dwelling, non-insect animals: Springtails, Diplurans and Proturans. They will be described first, for their evolutionary lineage represents an early branch of life from the arthropod clade “Hexapoda”: six-legged animals.
The Entognatha, Non-Insect Hexapods with Enclosed Mouthparts
Entognatha (Ancient Greek for “internal mouth”) make up around 20% of the non-insect hexapods. Within are three classes: Collembola (springtails), Diplura (diplurans) and Protura (proturans). Collectively, these are small creatures (averaging ~2 mm long) and either have poorly developed eyes or none at all. They are ground dwellers, living in moist soils and leaflitter, consuming decaying vegetation and fungi, with some predators of small invertebrates.
Insects are deemed Exognathous (“external mouth”) as their mouthparts are visible upon examination of the head. In Entognatha, the mandibles and maxillae are enclosed within the folds of the head at rest, and exposed when feeding. Another defining feature of Entognatha is indirect fertilization. Where insects (generally) mate via male penetrating the females, the Entognatha have a reproductive strategy that involves males depositing sperm bundles in their environment for the female to take up using her genital openings (Collembola & Diplura), or by actively transferring spermatophores to the female as in Protura (who can also use the aforementioned passive method from the other two classes).
Despite being non-insect hexapods, they are still classified as insects in the public eye, and Gullan & Cranston argue that these three classes should be deemed of equal rank to Insecta. Time for a detailed analysis:
Collembola (Springtails) Can Catapult Themselves Out of Harm’s Way
Springtails are around 2-3 mm with outliers at 17 mm. Their soft bodies have various shapes with “globular” and “elongated” being common (There are some 8,000 named species across 30 families; there’s bound to be more variety). Their bodies are either pale in colour, or in shades of black, blue and grey (good for camouflage in leaf litters). Their “springing organ” is a fusion of a pair of appendages called “furca”. It is longer in surface-dwelling species as opposed to those in soil, and the longer the furca, the greater the jump; up to 10 cm in some species.
Springtail eggs have small egg yolk reserves (“microlecithal”), which means embryonic development happens quickly as there is insufficient energy provided by the yolk to support more-complex development. This leads to “holoblastic cleavage”, in that the entire egg divides during every cleavage, and is closer to a vertebrate’s egg growth2. Males reach maturity after five moults, whereas females take longer, and moulting continues for life (unlike many insects who stop growing at the “adult” stage).
There’s Not Much Information on Diplura (Diplurans) & Protura (Proturans)
Diplurans have around a 1,000 species across ten families, ranging in size from 2-5 mm. They have well-developed mandibles and maxillae and lack eyes altogether. Their thorax is poorly differentiated from the abdomen, but you can tell it apart by the presence of legs. Their abdomen has ten segments with various “decorations” like hairs and vesicles protruding outwards. Some species have gregarious females, who nest together and/or tend to the eggs and young, otherwise embryogenesis is similar: holoblastic cleavage with oligolecithal eggs (“a little yolk”).
With Proturans, there 800 species, over half of which belong to the genus Eosentomon. They are the smallest of the three non-insect hexapods, at <2 mm in length. They are largely cryptic (“hard to find”), living in the soil and feeding on decaying plant material and fungi. Of the three, they are also the most primitive (implying they emerged first); no eyes or antennae, but they do have a sensory organ in their head termed “pseudoculus” (a “false eye”).
Archaeognatha the “Ancient Jaws”: Bristletails Have the Most Primitive Mouthparts
Our first insect order is the bristletails, a medium-sized soil dweller (6-25 mm long) with ~500 species in two families. They are classified as a “primitive” since adults are wingless and moult for life. Their mouthparts are exognathus (“external jaw”), pointing downwards. Bristletails have large compound eyes, a differentiation between the thorax and abdomen, and an ovipositor in females.
Fertilization occurs indirectly in a manner similar to the entognathous hexapods above, with the male leaving sperm outside for the female to pick up (or in rare instance, sperm is deposited directly on the ovipositor, rather than inside the female). Getting around when you’re flightless is done by running fast and jumping high: they arch their thorax and flex their abdomen to “spring” a fair distance.
Sidenote: Moulting for Life (“Ametabolous”) Vs. Moulting to Adulthood
The more primitive insects moult indefinity. It’s not the same as “growing indefinitely”, since subsequent moults have a minor role after sexual maturity (“adulthood”). A juvenile moults to grow, developing a larger exoskeleton, more muscles, larger organs and so on. Once matured, a species may either stop growing with subsequent moults (the entognaths above), or they grow very (very very) slowly, as with crustaceans and female mygalomorph spiders (tarantulas). For example, a lobster’s size continues increasing with diminishing returns after each moult, and this is termed “indeterminate growth”.
What of those arthropods who stop growing after adults? The additional moults are used to renew body structures that have been damaged or impacted by wear and tear. In springtails it can be the cuticle (their exoskeleton can be damaged by the environment [UV rays, surface abrasions etc…]), their sensory hairs (which may shed/fall off and require regeneration [without a trip to Turkey]) or their mouthparts (chewing plant matter is tough work).
Internal physiology also regenerates, as with the trachea and digestive organs. More remarkably is the regeneration of a lost leg or antennae, as each moult post-injury regenerates a portion of that missing structure3.
The metamorphic insects do not do this because maintaining their ecdysteroid cycles for lifelong moulting is energetically expensive. Better to maximise reproductive success at adulthood and make room for the next generation than to continue investing in the same organism.
Zygentoma, the “Yoked-Segmented Insects”: Silverfish Have Linked Symmetrical Structures Across the Body
The silverfish you see around the house belong to three genera of Zygentoma who are “synanthropic” – living with humans. Lepisma saccharina (the silverfish), Ctenolepisma longicaudata (the Long-tailed silverfish) & Thermobia domestica (the Firebrat, who favours the warm areas of the house). For simplicity, they are all dubbed “silverfish”, and their order Zygentoma includes ~600 species in five families.
They share some features with bristletails such as indirect fertilization and life-long moulting. The similarities stop at the head: instead of compound eyes they have some isolated ommatidia (the individual cells that makeup a compound eye) or none at all, with 1-3 simple ocelli present. Their mouthparts are “dicondylic”: two mandibles with two hinges rather than a single ball joint (as with bristletails), which makes for better chewing. Fertilization is also indirect, with females picking up male sperm from a substrate.
Majority of silverfish live in the soil, in litter or under bark. Some can live in caves or deserts (where they act as detritivores, consuming decaying/dead organic matter), and I’m sure you’re familiar with those domestic ones. If not, congratulations on having a very clean home(?), or staying up-to-date with your pest control.
Ephemeroptera, the “One-Day Wings”: Adult Mayflies Don’t Live Long
The first winged insect entry are the hemimetabolous mayflies, an order of ~3,000 species in 40 families, most of which are in the neotropical regions (i.e. the tropical Americas). Adults have reduced mouthparts (adults do not feed; many such cases), large compound eyes, and three ocelli, which is a “typical” flying insect structure. They have two pairs of wings: large triangular forewings and smaller hind wings.
The forelegs of males are elongated and used to grasp females during mating, who are fertilized directly during copulation. Their penultimate moult (the “subimago”, one stage before adulthood) is fully winged and mates, which is exceptional as it is the “almost” adult, rather than the “full” adult that mates and reproduces. Mating occurs in mating swarms over water or landmarks (but these landmarks are not as high up as those favoured by honey bee drone congregation areas).
Majority of species lay eggs in cool, fast-flowing streams, and the nymphs’ aquatic development depends on the species, requiring 12-45 instars (“stages”) until maturity. The duration ranges from 16 days in warmer conditions to over a year in colder and higher-latitude waters. Mayflies with shorter development cycles tend to be multivoltine, producing multiple generations per year. Nymphs can be aquatic detritivores, herbivorous (feeding on algae, fungi, diatoms) or predatory.
Odonata, “The Toothed Ones”: Dragonflies and Damselflies
The name “toothed ones” was given for the teeth of adults and larvae, who are predators in air and water respectively. There are two suborders: “Zygoptera”, referring to the “yoked wings” of damselflies, and “Epiprocta” (literal “upon the anus”4) dragonflies . Some 6,000 species are described, with 3,000 species in each suborder. Adults are medium-to-large, from (<2 cm to >15 cm), with the largest wingspan measuring 17 cm in the South American giant damselfly, Mecistogaster.
Adult Odonata have two large compound eyes and three ocelli. Their antennae are short as their hunting is done visually. The thorax is enlarged to house their two (large) pairs of wings, richly veined for increased oxygen transport and subsequent flight performance. Their abdomen has ten segments, terminating in the clasping organs used in reproduction. Mating occurs when a male grasps a female by her neck (anatomically, the “prothorax”) and the pair fly in tandem towards a perch, lasting for seconds or several hours. The female lays eggs onto a water surface, whether it’s mud, sand or plant tissue, and the hatchling (“pro-nymph”) immediately moults into its predatory nymphal form.
Odonata Nymphs Are Predatory in All Life’s Stages
Moulting duration varies in nymphs, with up to 20 instars being recorded for some species. All stages have fully-developed mouthparts, with wings developing in older instars. Dragonfly nymphs tend to be “squatter”, with a head that’s the same width as their thorax, whereas damselflies are more elongated, with the abdomen generally ending in three gills (“caudal lamellae”: paddle-like structures used for respiration, propulsion, and predator avoidance). There is an “anal pyramid” in many dragonflies that they use for rapidly ejecting water akin to jet propulsion; a useful escape mechanism.
Nymphs eat other aquatic organisms, whereas adults catch aerial prey. The adults are long-lived (measured in weeks), whereas nymphal stages can take years depending on the climate and species. Nymphs prefer well-oxygenated still waters (ponds, lakes), and can tolerate turbulent, warmer conditions.
Sidenote: How Did the Taxonomical Classifications Come to Be?
The “traditional” classifications (“Linnaean Taxonomy”) were published by Carl Linneaus in 1735 and were based on observable differences like anatomy, behaviour, environmental relatedness and so on. It was relatively simple: “Kingdom, Phylum, Class, Order, Family, Genus, Species”, and had cheery highschool mnemonics like “King Philip Came Over For Good Soup” (as is the case with teenage boys being boys, the genus-species classification often changed from “Good Soup” to… uh…. homosexual copulation). Note that “Domain” came later following the work of microbiologists; Linnaeus started with “Kingdom.
As science and technology advanced, knowledge of evolution and the fossil record refined the Linnean system into more-flexible hierarchies, partially governed by the International Code of Zoological Nomenclature (“ICZN”) at the Family, Genus & Species levels. Above the family level (Order, Class, Phylum, etc.) there are no internationally “regulated” groupings, and so taxonomists can introduce as many subgroups as needed, as is the case with our Odonata infraorder “Anisoptera”. A comparison table is provided at the end of this article, and honey bees are discussed in “the scientific name of bees”.
Plecoptera, the “Woven Wings”: Stoneflies Have Extensive Wing Vein Patterns
Stoneflies are an order of 4,000 species across 16 families within temperate and cool areas. They are hemimetabolous, with nymphs occupying aquatic environments and the adults are airborne. Nymphs resemble miniature adults (a phrase you’ll re-read throughout these entries), and the transition from nymph to adult is without fanfare, often descried as “a nymph with wings”. Adults have two bulging compound eyes, two or three ocelli, two pairs of (long) wings that extend beyond the abdominal apex and three pairs of legs.
Nymphs average 10-24 aquatic instars, with some species going to 33. Mandibles are fully developed, and in most species, wings become visible halfway through their nymphal lifecycle. Stoneflies mate during the day and the eggs are laid in the water, either directly, on a jelly secretion or underneath stones/crevices near a body of water. Development can take up to three years in some species, with the general trend being that the colder the climate, the slower the development.
Nymphal diets vary from predatory to detritovory or omnivory. Adults are herbivorous, with some short-lived species foregoing food altogether (“mate quick, die quick” once again). Nymphs are found on stony/gravelly substrates in well aerated, cool water (hence “stone” flies). When they reach their penultimate moult (“sub-imago”), they crawl to the water’s edge, moult one last time into adulthood and become airborne.
Dermaptera, “Leathery Wings”: Earwigs Have Short, Leathery Forewings that Protect the (Much) Larger Membranous Hindwings
Earwigs have some 2,000 species in 11 families. They are hemimetabolous, with long and flattened bodies. Compound eyes vary between species: some have large ones, others small, and some absent; they have no ocelli. Their antennae are short, and one way to distinguish nymphs from adults is in antenna length, as there are fewer segments in immature individuals. Some earwig species have wings, others are without (“apterous”). Those with wings have a small and leathery forewings, whereas the hindwings are large and membranous with a semi-circular appearance (perhaps the name “ear” wig comes from the shapes the hindwings make at rest?).
One defining feature of an adult earwig are the abdominal cerci-cum-forceps. The cercus refers to sensory appendage located at the very tip of an insect’s abdomen; they come in pairs, hence “cerci”. The forceps are used in manipulating prey, offense, defence, and in some species, mating. Females lay eggs in burrows made of debris, where they often guard them from predation and “lick” them clean to remove accumulated fungi (soil is a microorganismal warzone). Some females will stay and care for nymphs until their second or third instar. It takes four or five moults to reach maturity.
Earwigs are nocturnal, and despite having wings, they are adapted for walking/running long distances (legs are “cursorial”). They feed on dead and decaying vegetable and animal matter, with some species being predators, and others garden pests. The Arixeniidae family live amongst bats in South East Asia (either as parasites or within commensal relationships), whereas the Hemimeridae family are semi-parasites of African rodents (specifically the giant murid rodents Cricetomys spp. & Beamys spp.. They feed on skin flakes, fungi and body secretions from their rodent host’s skin.)
Zoraptera, the “Purely Wingless”: When the Angel Insect Order was Established, Only Wingless Specimens Were Known
Angel insects have 40 species belonging to the one genus Zorotypus and are found in tropical and warm temperate regions around the world (except Australia). They are rarely encountered and not much is known about them relative to others (they were first described in 1910s). Zorapterans are small, <4 mm long and appear termite-like in shape. Winged species have ocelli and compound eyes, and the wingless ones do not. Wing shapes depend on the sex (“polymorphic”), some forms are wingless in both sexes, others have winged reproductives (“alates”) with two pairs of paddle-shaped wings, with the forewings being larger than the hindwings.
Angel insects are hemimetabolous, dwelling in leaf litter, rotting wood or near termite colonies (perhaps that’s why they look like termites… could they be partaking in a form of mimicry?). They act as decomposers, consuming detritus and assisting in nutrient cycling within the soil. Zorapterans live gregariously, with some species nesting in colonies.
Recent phylogenomic work from Wang and colleagues determined that Zoraptera is a sister group to Dermaptera (earwig) & Plecoptera (stoneflies), marking them as having shared a most recent common ancestor. For those interested, the article is free to read: Wang et al., 2026.
Orthoptera, the “‘Correct’ (or “Upright”) Wings”: Crickets & Katydids have Upright Wings
Crickets, grasshoppers, locusts and katydids – if you’ve been in a garden, you’ve probably seen one and heard many. Orthoptera are found worldwide, with 24,00 described species in ~40 families (the classification number is contested; some entomologists are nitpicky). They are lumped into two suborders based on the shape of the females’ ovipositor:
- Caelifera for grasshoppers and locusts.
- Meaning “chisel-bearing”, as females have a short, stout, solid-looking ovipositor that resembles a chisel.
- Ensifera for katydids and crickets.
- “Sword-bearing”. Females have a long, straight ovipositor resembling a sword.
Orthopterans are hemimetabolous and have bodies shaped like an elongated cylinder. Their hind legs are enlarged for jumping (amongst other things, like chirping in Caeliferan males and mediating the “ravenousness” state in migratory locusts). Their compound eyes are well-developed, and ocelli may or may not be present, depending on the species. Their forewings are thickened, leathery and narrow (called “tegmina”), with much broader hindwings.
Grasshoppers and locusts are predominantly active during the day. They move fast, have sharp vision and are herbivorous. Their herbivory makes them garden pests, with the most extreme outcome being the migratory “plague” locusts. Katydids and crickets tend to be nocturnal, possessing camouflage or mimicry and long (long, long) antennae relative to the Caeliferans. They can be predatory, omnivorous or phytophagic (phytophagy is a specialised form of herbivory describing organisms that feed on plant tissues or sap).
Singing and Chirping in Orthoptera: Male Mating Calls
Male Orthopterans sing. Grasshoppers and locusts scrape their hindlegs against their forewings, whereas crickets and katydids rub their forewings together (“stridulation”) to produce these audible vibrations. Some locust and grasshopper species produce sound by crepitation, snapping open the hindwings during flight, or snapping it at rest. Some produce sounds by rubbing their tibias against the abdomen.
If a female likes that particular male’s call, they copulate. The male mounts the female and the process can take several hours. Our chisel-shaped ovipositor Ensiferans lay eggs into soft surfaces like plants or soil, whereas the sword-like ovipositor of Caeliferans buries eggs in soil chambers. The emerging nymphs look like adults, minus the wings. In wingless species, it is difficult to distinguish between a reproductive adult and a large nymph.
Embioptera, “Winged Weavers”: Webspinners Produce Silk from Their Forelegs
Webspinners are a soil-dwelling order consisting of 450 described species in 13 families. Their name is attributed to the silk produced from glands on their forelegs which they manipulate into forming tunnels, sheets and/or branching galleries beneath bark, rocks and other solid materials. The silken glands are present in both sexes and all instars.
Adults range from small-to-moderate sizes with an elongated, cylindrical body. Compound eyes are kidney-shaped (“reniform”) and are larger in males than females. All females and some males are wingless. If a male has wings, they are soft and flexible. Their legs are short, and the basal segment of each foreleg is swollen with the silks glands. The immature stages resemble the adults with the exception of wings (if present) and genitalia (bring out your magnifying lens).
Webspinners are gregarious, with females tending to eggs and younger nymphs, sometimes feeding them chewed up plant material. Within their silken galleries, they feed on litter, moss, bark and leaves. If they need to seek new food sources, the silks are extended so that the webspinners remain within their safety. Mature males leave the gallery for mating. They do not eat and are often cannibalised by the female after copulation.
Sidenote: Are Webspinners the Insect Order Whose Behaviour Mostly Closely Resembles Spiders?
Sharp-eyed readers may note similarities between Embiopterans and the spider order Araneae. It’s not phylogenetically relatedness, as the fossil record suggests that spiders came before insects by ~18 million years. What is similar are their behaviours:
- Both produce silk from glands
- Both live in silk-constructed dwellings where they spend their entire life
- Males are the ones who disperse for mating purposes
- Males are often eaten by the female after mating
- The mother takes care of eggs and the very-young brood
That’s about it as far as resemblances go, since webspinners are detritivores and spiders carnivores. A Google/LLM search for “which insect most closely resembles spiders in behaviour or adaptations” returns results for insects-mimicking spiders. Nothing wrong with mimics, as these results answer the question for many people. Still, the relationship between webspinners and spiders hints at convergent evolution, as their spin-webs-cannibalise-males-care-for-brood approach independently evolved in these two unrelated orders owing to success of these adaptations within their niche.
Phasmatodea, the “Phantom-Like Insects”: Stick Insects Appear and Disappear within Vegetation like g-g-GHOSTS
Run scoobs!
Stick and leaf insects are a mostly-tropical tree-dwelling insect order with worldwide distribution, consisting of ~3,000 species. The number of taxonomic families varies from 5 to 13 according to the sources. Their name comes from their stick-like appearances which is a part of their anti-predator defence. They are generally slow movers, take on grotesque and asymmetrical postures and often “play dead” (“feigning death”), all to fool a predator in viewing them as part of the plant. Some species can also eject noxious chemicals from their thoratic glands.
Phasmatodeans are hemimetabolous, with nymphs resembling smaller adults that lack wings and developed genitalia. Most stick insects are wingless, and in winged species only the males have functional wings, which they use for travelling to new locations for mating. Winged males have ocelli. A stick insect’s compound eyes are front-and-sideways facing (“anterolaterally”) rather than being full frontal. Their long legs can be shed in the nymphal phase as a predator defence and later regrown in subsequent moults.
They are tree-like all the way down to the eggs, which look like small seeds. Copulation involves the smaller male mounting the female, and unless you look closely, it will seem like another twig on another branch. All these behaviours evolved in response to visual predators: birds, lizards and spiders are considered their main predators. For further reading: see Bian, Elgar & Peter’s 2016 paper on the swaying behaviour of Macleay’s Spectre (Extatosoma tiaratum).
Grylloblattodea, the “Cricket-Cockroach-Like Insects”: Rock Crawlers Have a Long Lifespan of Five Years
Within the order Grylloblattodea is one family, Grylloblattidea, which contains 32 described species within Western North American and Central-to-Eastern Asia. This is the first insect order that contains more extinct than extant (“living”) specimens with over 500 species identified by the fossil record. Both species prefer cold climates, with North American varieties living at high elevations on glaciers and snow banks (hence their other common name, “ice crawlers”); Asian species prefer mountainous terrain and cool temperate forests.
A rock crawler is moderate in size, around 14-35 mm long with reduced or no compound eyes. They also lack ocelli and wings, so their sensory systems are primarily non-visual. Males have asymmetrical genitalia and tend to mate in a sideways fashion: male on the right, female on the left. Eggs are deposited under damp woods or stones and remain inactive for a year before hatching (“diapause”). Nymphs resemble adults and have slow development in eight instars (cooler temperatures probably contribute to this).
Rock crawlers are active in low temperatures both day and night, feeding on dead arthropods and organic materials found on the surface of ice and snow during snow melts, in caves, alpine soils, or damp paces beneath rocks. Such a specialisation on cold conditions makes them particularly susceptible to the increasing temperatures associated with climate change (e.g. Schoville et al., 2020).
Mantophasmatodea, the “Mantis-Stick-Insect-Like Insects”: Heelwalkers Have Characteristics Resembling Both Mantises & Stick Insects
As an order, Heelwalkers were recently classified (2002!) following analysis of 45 million-years-old Baltic amber specimens. The preserved creatures bore similarities to both praying mantises and stick insects but did could not be assigned to either order. Shortly afterwards came museum species from Southern Africa (Namibia & Tanzania) that once compared to the fossils, were found to be related to both orders, thus “Mantophasmatodea” was born. There are two or three living heelwalker families, perhaps 12 extinct (a disputed number), and 20 described living species. (Being a recently-named taxonomy, the number of species is also highly contested amongst the pointy heads).
Living heelwalkers are found in southwestern Africa, around Namibia and South Africa (on karoo and fynbos vegetations). They are moderate in size, up to 25 mm long and are completely wingless (not even rudimentary or primitive winglets). Their legs have five segments, and their “heelwalker” moniker comes from their enlarged arolium, the pad on the bottom of insect feet that helps them grip onto smooth surfaces. This enlargement causes their fifth leg segment (the “distal tarsomere”) to be raised above the substrate, hence “heelwalkers” (their fourth segment is the “heel”). Additionally, their hind legs are elongated and can be used for small jumps.
Heelwalkers communicate via vibrations generated by drumming their abdomen on the substrate, and an enlarged arolium makes for better detection. Copulation is prolonged, with some species taking up to three days. Males are often eaten after mating. Eggs are laid in pods made of sand grains and covered with a water-resistant secretion (they live in dry environments). Nymphal development coincides with wetter months of the year, and after each moult they eat their discarded cuticle.
They can be ground dwelling or living on shrubs/grasses, occurring singularly or as a mating pair. South African species are nocturnal and the Namibian species diurnal. They are predators, feeding on small flies, bugs and moths, using their spines on their front & middle legs in combat with their prey, hence an alternative common name to these heelwalkers is “gladiators”.
Mantodea, the “Prophet-Like Insects”: A “Mantis” in Ancient Greece was a Prophet or Seer, not an Insect.
Mantodea is the order of praying mantises, carnivorous insects with an iconic “praying” pose formed by the clasping of their forelegs. Their order contains around 2,400 described species across 8-15 families. Their size ranges from moderate to large, 1-15 cm long with a hemimetabolous lifecycle. Heads are small, triangular and mobile, the antennae large and slender (and also highly mobile). Eyes are widely separated. Their forewings are leathery and the hind wings are broad and membranous, although some species can have minimal or no-wings.
The forelegs are akin to those of a raptor (hence “raptorial”), used for striking and grasping prey. The mid- and hind legs are elongated for walking. Females sometimes consume the males during or after copulation (a “thank you” for the superb effort he puts into courtship rituals). Mantis eggs are laid in an ootheca, a protective egg casing that hardens on contact with the air. Some females guard their eggs. Upon hatching, the first instar nymph moults into the second instar immediately. Nymphs of some species require three instars to reach maturity, others up to 12. As with other hemimetabolous insects, nymphs resemble miniature adults, minus the wings and genitalia.
A mantis is a sit-and-wait predator. Their heads are fully mobile, and their excellent vision helps them detect prey. Their colouration makes them camouflaged hunters, waiting for the prey gets close before striking. Their wings can be used in short bursts to escape from predators.
Blattodea, “Insects That Avoid the Light”: If You See Cockroaches Active During the Day, You Could Be in Trouble
A pest controller once told me that seeing one roach in your home in broad daylight means its injured, dying, or under the influence of pesticides and is a non-issue. It’s when you see multiple active roaches that the trouble begins, as it’s a sign their colony is overcrowded, forcing them to spend time outside… I didn’t’ think much of his words until I encountered a German cockroach-infested house and then I understood. Not a pleasant experience.
Blattodea used to solely contain cockroaches. Following molecular analysis, it expanded to include termites as they are very similar to roaches phylogenetically. There are some 4,500 species of cockroaches, in more than five families, and only a handful of species are household pests. They are hemimetabolous insects varying in size from small to large (<3 mm to > 100 mm). Compound eyes are moderately large to small, or absent in cave-dwelling species. Ocelli are two pale spots on the top of the head. Their prothorax is enlarged and gives them a shield-like appearance that covers the head. Their forewings are hardened (sclerotized) to protect he membranous hind wings (“tegmentum”). Their legs are covered in spines (termed “spinose”, good for predator defence).
Mating in cockroaches is end-to-end, with females sometimes mounting the male prior to commencement. Both sexes produce courtship pheromones as well as sounds (“stridulatory courtship”). Eggs are laid in a protective casing (the ootheca) and may be carried externally by the female. Nymphs generally develop slowly and resemble miniature adults minus the wings and genitalia.
It’s unfortunate that we’ve labelled the entire order as “undesirable” based on our experiences with the (rightfully-detested) household roaches. The typical cockroach is a tropical species that is either nocturnal or diurnal; sometimes they live in trees or caves. Some are solitary, others gregarious. Most cockroaches are scavengers and some eat decaying wood. Like termites, they have mutualistic bacteria in their fat body (Blattabacterium) that assist in metabolising nitrogenous wastes, and is one of the reasons why they can subsist on a diet of pretty much anything.
The Former Isoptera (“Equal Wings”), Now a Blattodea Epifamily: Termitoidae
There are some 3,000 termite species, with 70% of them in the family Termitidae (although seven to nine families are recognised, with 16 subfamilies). Within the order Blattodea, they are in a clade called “dictyoptera” (the “net wings”, named for their complex wing vein patterns). Termites are hemimetabolous and live in social colonies with a caste system: workers, reproductives and soldiers.
All stages are small to moderate in size, <20 mm long. Soldiers tend to have enlarged mouthparts and body features, whereas a worker is more “muted” in appearance. Most species have reduced compound eyes, along with a long, multi-segmented antennae. Their wings are membranous and both pairs are similar in appearance (except the Mastotermes species, which have complex venation). The non-reproductive workers do not have viable genitalia (similar to other eusocial insects with caste differentiation), with Mastotermes spp. being an exception.
Termites have symbiotic bacteria in their gut that helps them break down cellulose-rich woody material. The workers feed nymphs and newly-moulted individuals via trophallaxis (mouth-to-mouth food exchange), which is a driving force behind their sociality. Nests are created in wood (or your home’s timber batons), ranging from rotting timber or an otherwise-healthy tree. Nest architecture ranges from simple mounds to galleries to complex structures like the above-ground termite mounds.
Termites play the role of decomposers and are particularly important to tropical lowland ecosystems where they recycle biomass. Up to 95% of the tropical soil insect biomass can consist of termites. Despite this, the public perception is that they are pests of crops, trees, woods and homes, many such cases. As it stands, less than 200 species are classified as pests.
Psocoptera & Phthiraptera: the Two Orders of Lice Used to Be in One Superorder: Psocodea
Lice used to be one group belonging to the superorder “Psocodea”, and now they’re split into two orders: Psocoptera and Phthiraptera. Psocoptera are the bark lice and book lice, which are some 6,000 species in various suborders: Bark lice (Psocomorpha), as well as intermediate or “hybrid” orders that contain both book lice and bark lice: Trogiomorpha & Troctomorpha. The “true lice” that parasitises you and me are in Phthiraptera.
Psocopterans, “Worn-Away Wings”: Non-Parasitic Louse are Hard to Find
Non-parasitic lice are cryptic and hard find. They range from minute to small (1-10 mm) with hemimetabolous development (if an adult louse is already small, how much smaller is a nymph?). Maturity is reached after five to six nymphal instars, with adults having a large, mobile head and large compound eyes. Winged species have three ocelli for light sensing during flight). The presence of wings influences thorax structure, with winged species having larger thoraxes. At rest, the wings are held in a roof-life manner above the abdomen.
After mating in a nuptial dance, a louse lays eggs in groups or as single units onto vegetation or under bark, where the nymphs develop. Females in some species do not mate and instead reproduce parthenogenetically, with the offspring being identical to their mothers. Some lice are solitary and many others are communal, living in small groups of adults and nymphs underneath silken webs spun by the adults (applicable for bark lice, whose silken “glue glands” are located in their mouthparts).
The non-parasitic lice’s diet consists of fungi, lichens, algae or insect legs. Some may be scavengers of dead organic matter, whereas the parasitic louse feeds on bits of you and me. It is likely that the parasitic lice evolved from the free-living bark and book lice. Over evolutionary time, this relationship became so specialised that the parasitic louse cannot survive outside their host (“host-specificity”); they have lost those survival mechanisms.
Phthiraptera, “Louse-Winged”: Parasitic Lice are Wingless & Have Extreme Specificity; They are Unlikely to Survive on a Non-Host Species
Depending on the species, a parasitic louse may feed on bird feathers, mammalian skin or blood. Their eyes are either absent or reduced (why would you need vision if you are not going to leave your host?), their thorax tends to be fused (rather than multisegmented) and legs are well developed with strong claws for grasping the host’s hair or fur, which is where they lay eggs.
The remaining four suborders of Psocodea are parasitic lice – if “Psocomorpha” refers to the book and bark lice, then “Phthiraptera” refers to the “true” lice. Nowadays, Phthiraptera is split into four suborders:
- Rhynchophthirina, a small group of lice found in Africa on elephants, warthogs and bush pigs
- Amblycera and Ischnocera, a worldwide lice group that makeup the chewing and biting lice
- Anoplura, the lice who possess beak-like mouthparts for piercing and sucking.
Sidenote: Is Bat Fur’s Electric Charge the Reason Why Bats Don’t Get Lice?
Lice are found on all orders of birds and almost all orders of mammals except for bats, why don’t bats get lice? The short answer is that “The absence of lice in bats is a direct consequence of their adaptation to active flight” (Abstract of Shchelkanov, 2021… The remaining text is in Russian). The longer answer has to do with electrification of bat fur. First, some background:
After running the PDF through a translator, the author states that lice are highly specialised, with each species (generally) parasitising one host – if you took a human louse and transferred it to a dog or silverback gorilla, it would not survive. There are no lice in hairless mammals (e.g. hippos, dolphins [aquatic lice], rhinos), however some hairy mammals also do not have lice (sloths and anteaters), so the presence of hair is not a determining factor for the presence of lice.
As bats fly, they develop a positive charge on their hairs as a result of friction with air and the particles within it. This spreads the hairs further apart (recall that identical charges repel one another & opposites attract). As a result, the louse has difficulty gripping their fur or membranous wing surfaces, thus preventing parasitisation. The paper ends there. I would add that should a louse get a lucky grip, the social grooming in bats is another defensive layer that would remove our brave adventurer.
Thysanoptera, the “Fringed-Winged Insects”: Thrips Have Hairs on Their Wing Tips.
Thrips are tiny creatures, from 0.5 mm to 1.5 mm in length with some 6000 described species in two suborders: Terebrantia and Tubulifera. Thrip development is hemimetabolous-converging-on-holometabolous: they have instars that act as larvae5.
Their compound eyes range from large or small, with the presence of ocelli being dependent on the presence of two pairs of wings. Winged thrips also have larger thoraxes (you’ve got to fit them in somewhere). Wings are slender with a long fringe of hairs (“setae”). One way to distinguish between the Terebrantia and Tubulifera thrip suborders is by their resting wing placement: the former has them parallel on the body and the latter has them overlapping atop one another. Their legs are short and adapted for walking, in some species they are “raptorial”, used for hunting prey. Abdomen-wise, the females lack cerci, which is useful to distinguish between sexes.
Terebrantia females lay eggs into plant tissue, whilst Tubulifera opts for crevices or exposed vegetation. The first and second instar nymphs follow the miniature-looking-adult pattern, yet are called “larvae”. The remaining instars (numbers 3-4 for Terebrantia and 3-5 for Tubulifera) are akin to pupal stages, since this larva-nymph is at rest; growth involves significant internal restructuring, akin to the larvae of holometabolous insects. Like honey bees (and other bees/wasps), males are born from unfertilized eggs (“haploid”) and females from fertilized eggs (“diploid”).
The thrip diet started out on fungi, then branched into phytophagy (consuming flowers or leaves), or predatory (those with raptorial forelegs are such candidates). A plant-feeding thrip uses its mouthparts to suck up plant matter, whereas pollen- and spore-feeders consume the individual grains/spores respectively. Some thrips are pollinators; others are vectors of plant viruses.
Hemiptera, “Half Wings”: The True Bugs are a Large Order of Sucking Insects
Hemiptera is vast and these few paragraphs will not do them justice. Originally, the order was named for the “true bugs”: those plant-feeding insects with sucking mouthparts. Entomologically speaking, if it’s not Hemiptera, then it’s not a bug, it’s an insect. As entomology progressed, Hemiptera was divided into two suborders: Heteroptera for the “true” bugs & Homoptera (“same wings”) for cicadas, leafhoppers, planthoppers, treehoppers, jumping plant lice [why not plant-lice-hoppers?] hip-hoppers, aphids, spittle bugs, lindy hoppers… the list goes on. Today, there are five suborders:
- Heteroptera, the true bugs,
- Coleorrhyncha, the moss bugs (of the family Peloridiidae),
- Cicadomorpha, the cicadas, spittle bugs and tree/leaf hoppers,
- Fulgoromorpha, the planthoppers, and
- Sternorrhyncha, the aphids, plant lice, whiteflies, scale insects and other gardening undesirables.
Given the variety of physical appearances (from cicada to an aphid), the descriptions of Hemipterans will be (very) general.
Compound eyes are large; ocelli may or may not be present. Antennae tend to be short with few segments. The mouthparts are modified as needle-like stylets that ultimately form a proboscis for piercing and sucking plant material. Thorax size depends on the presence of two pairs of wings, which may not always be present (male scale insects may only have one pair of wings). Legs are built for walking, with raptor-like forelegs in predatory species (mostly in Heteroptera; e.g. ambush bugs as described by Weirauch et al., 2011).
The “half wings” naming comes from their forewings, which are thick and leathery at the basal end (towards the body) and thin and membranous at the distal end (near the apex). This “hemelytra” is a half-hardened wing that entomologists use as a classification hallmark for Hemipterans.
This is the final hemimetabolous entry, and you know how it goes: nymphs resemble miniature adults, and eggs are laid in a variety of location. Some members like aphids, are “viviparous”, giving birth to live young (some of which are born mated… aphid biology!). Parthenogenesis is present (again in aphids), with some seasonal sexual reproduction. Some stages of Coccoidea (scale insects) have nymphal stages that are larval in appearance, followed by “pupal stages” suggesting a convergence towards holometabolous development (as opposed to “evolution”).
Our day-to-day interactions with hemipterans are with those who appear as garden pests. They suck on plant tissue, some form galls, lerps or tunnels. Others dehydrate a plant, or spread disease… there are many bugs. The non-plant feeding Hemipterans tend to be predators, scavengers, bloodsuckers, or necrophages (consuming dead prey), with the lattermost group being successful in aquatic environments owing to the abundance of unclaimed dead meat in the ocean.
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Appendix: Common Taxonomic Hierarchies in Zoology
| Rank | Prefix Meaning | A Classification Example Using the European Honey Bee |
| Domain | — | Eukaryota (an organism whose cells contain membrane-bound organelles) |
| Kingdom | — | Animalia (an animal) |
| Subkingdom | below kingdom | Eumetazoa (a “true” animal [excludes sea sponges; phylum: Porifera] |
| Infrakingdom | below subkingdom | Bilateria (bodies exhibit bilateral symmetry; divided into identical left and right halves) |
| Superphylum | above phylum | Ecdysozoa (undergoes ecdysis; shedding/moulting of their exoskeleton) |
| Phylum | — | Arthropoda (jointed appendages – legs, antennae, mouthparts) |
| Subphylum | below phylum | Hexapoda (six-legged) |
| Infraphylum | below subphylum | Atelocerata (a dated term for “incomplete horns” [antennae] no longer used & only included here to demonstrate an infraphylum) |
| Superclass | above class | Hexapoda (as taxonomy is not governed above the family level, some taxonomists classify Hexapoda as a “superclass” instead of subphylum… oh won’t somebody please think of the children??) |
| Class | — | Insecta (“a cut-up [segmented] body”) |
| Subclass | below class | Pterygota (“winged ones”) |
| Infraclass | below subclass | Neoptera (“new wings” – they evolved the ability to fold their wings flat over the abdomen, unlike the more primitive insects [e.g. dragonflies & mayflies], who cannot fold their wings in this manner) |
| Cohort | Variable placement (lovely!) | Endopterygota (“internal wings”, as in, wings develop internally during the pupal phase) |
| Superorder | above order | Holometabola (“Complete transformation”, or complete “metamorphosis”: Egg → Larva → Pupa → Adult) |
| Order | — | Hymenoptera (“married wings” – the wings of bees are joined together by hooks called hamuli that joins them into one unit for more efficient flight) |
| Suborder | below order | Apocrita (“separated”, as with the “wasp-waist” effect – first abdominal segment is fused to the thorax and the remaining abdomen is constricted in appearance) |
| Infraorder | below suborder | Aculeata (“the stingers” because well, you know why) |
| Parvorder | below infraorder | Used in some insect groups, but not in the case of bees |
| Superfamily | above family | Apoidea (“bee-like” in appearance) |
| Family | — | Apidae (“the Apis family”) |
| Subfamily | below family | Apinae (“the Apis subfamily”) |
| Tribe | below subfamily | Apini (“the Apis Tribe” [very creative]) |
| Subtribe | below tribe | Apina (I bet you can figure this out) |
| Genus | — | Apis (Latin for… Bee!) |
| Subgenus | below genus | Apis (Apis) (no distinct subgenus for honey bees) |
| Species | — | Apis mellifera (honey bee, translates to “honey carrier”) |
| Subspecies | below species | Apis mellifera ligustica (“the Italian honey bee”) |
Footnotes
- Part Two on holometabolous insects can be found here ↩︎
- True insects have “centrolecithal” eggs with large quantities of yolk. This does not permit complete cell division (the yolk is not a “living thing”), so when insect eggs divide, it is “superficial cleavage”, only the nucleus is dividing each time. These nuclei migrate to the egg surface, which is when the membranes form and they become separate cells. Until then, the embryo is a single, giant, multinucleate called a syncytium. (For reference, the syncytium then forms a blastoderm, which then leads to a germ band & finally an insect embryo). ↩︎
- The short answer is that “regeneration” is triggered locally at the site of injury. During the time in between moults (“intermoult period”), the lost appendage is rebuilt as a miniature limb (via a mass of undifferentiated cells “blastema”) that unfolds and expands into a new external limb. It takes several moults for the restored limb to reach its previous size. ↩︎
- Named for the “epiproct”, a dorsal appendage located immediately above the anus. Before they were called “Anisoptera”, the “unequal wings”, as the hindwings were enlarged for better flight manoeuvrability. Following molecular and phylogenetic studies, Anisoptera was relegated to the classification as an “infraorder” within the suborder Epiprocta. ↩︎
- It’s not that thrips are evolving to become holometabolous, rather they have evolved their own form of holometaboly independently of the other orders. The thrip “larvae” still look miniature adults with compound eyes, wing buds, adult-like legs & body segments, and they also compete with adults for food. It’s the “prepupa” & “pupa” phases that are closer to a holometabolous pupa, since the larva stops feeding, decreases its movements and the wing buds enlarge/tissues reorganize internally.
It’s still a nymph, only “pupal-like” in behaviour. There are no imaginal discs (those clusters of undifferentiated cells that build the adult body), and their existing tissue is directly remodelled during that prepupal phase. ↩︎