Holometabolous Insect Orders: An Overview

The Success of Metamorphosis as a Development Strategy

Some eighty percent of insects undergo complete metamorphosis (“holometaboly”) to reach adulthood, and this lifecycle can be summarised in four steps: egg –> larva –> pupa –> adult. This contrasts the incomplete metamorphosis (“hemimetabolous”) insect lifecycle of egg –> nymph –> nymph –> yet-another nymph –> wow, more nymph?.. –> adult.

The success of holometaboly is in reducing parent-offspring competition: the larva’s diet, habitat, predators, and (less-importantly) lifespan & active periods, do not overlap with the adult, increasing the chances of survival for both parent and offspring. I will discuss the holometabola in accordance with the fifth edition of Gullan & Cranston’s “The Insects”. There are nine orders of holometabolous insects (compared to the ~18 or so hemimetabolous orders), and it these nine that will be discussed here, with tangents provided by Yours Truly.

Neuropterida: A Superorder Containing Neuroptera, Megaloptera & Raphidioptera

The earlier article on hemimetabolous insect orders discussed the taxonomic classifications and how the classification rules were fluid above the “family” level. If you believe that an order should be a superorder, a suborder, a superfamily or something else, you are welcome to do so, provided you can back up the claims; there is no governing body to regulate your decision. Neuropterida is one such example, it can be a clade (“natural group”) or a superorder. In this article, they’re treated as a superorder.

Within the superorder Neuropterida are three orders:

• Neuroptera (lacewings, owlflies & antlions) – 6,500 species in ~20 families.
• Megaloptera (alderflies, dobsonflies) – 350 species in two families (Sialidae and Corydalidae respectively).
• Raphidioptera (snakeflies) – 200 species in two families.

Common features to all three are multisegmented antennae, large & separated, compound eyes and mandibulate mouthparts¹. Leg structure is generally non-specialised, except in predatory species, where they are adapted for hunting. They have two pairs of wings that are similar in shape, which extend beyond the abdomen when folded at rest.

Neuroptera, “Vein-Winged Wings”: Lacewings Have Numerous Cross-Veins & “Twiggings”

Both adult and larval lacewings are predatory, with some adult species consuming nectar, honeydew or pollen instead. Their larvae’s predatory speciality depends on the Neuropteran family: Mantispidae (Mantid lacewings) consume spider egg-masses, Sisyridae (spongeflies) consume freshwater sponges and the three families Chrysopidae, Hemerobiidae and Coniopterygidae prey on soft bodied hemipterans (“true bugs”) like aphids and scale insects.

Megaloptera, “Large-Winged Insects”: Dobsonflies Have One of the Largest Wings Among Holometabolous Insects

Megaloptera larvae are aquatic predators and scavengers with well-developed mouthparts. The “hellgrammite” is the common name given to Dobsonfly larvae, probably by fishermen in North America who use them as bait. Larval growth involves 10-12 instars with an average timeline of 2-3 years. Larvae spend their time under rocks or logs in “clean” rivers, as they are intolerant of pollution², and their presence is an indicator of a healthy river. Mature larvae crawl onto land towards damp soil or underneath logs to being pupating.

Megaloptera pupae appear beetle-like and are fully motile due to their free legs (“exarate”). This mobility is used to defend against predators rather than further feeding (the pupal phase is where the larval body rearranges into the adult form… remarkable to manage that while remaining mobile). Despite their large mandibles, adults are short-lived and generally do not feed (or if they do, it’s on a liquid diet of nectar). Males use their mouthparts in mating and for competition with other males, the goal being to “flip” the opponent and lower his prospects of reproducing in their immediate-future.

Raphidioptera, “Needle-Winged Insects.”: Snakeflies Have A Long “Neck” (Prothorax), Providing A Snake-Like Posture

The order’s name “Raphidioptera” does not refer to the wings, rather their overall slender & elongated appearance: a “needle-like body”; the “-ptera” suffix is added as part of naming conventions.  Both larvae and adults are predators, with their distribution being limited to the Holarctic region within the Northern Hemisphere. Adults look mantid-like due to their elongated prothorax (as opposed to the raptorial forelegs seen in the mantis family Mantidae). Their mobile head is used to strike at prey in a snake-like manner, which is score two for their common name “snakefly”.

Raphidioptera females have a long ovipositor for laying eggs into crevices or under bark, where the larvae develop over a period of one-to-several years in 10-11 (or more) instars. They are a bit like my apple trees, in that they require periods of low temperatures (“chill”) to induce pupation or trigger adult emergence from the pupa in late-stage pupation (“eclosion”).

Sidenote: Biogeographic Realms are Evolutionary Regions That Describe an Organism’s Origins

In biology, you hear about “Biogeographic Realms”. The planet Earth is divided into eight³ terrestrial realms. They are the:

• Palearctic, which holds the bulk of Europe, Asia & North Africa.
• Nearctic, which contains Greenland & most of North America.
  • When grouped, the Nearctic & Palearctic make up the “Holarctic”.
• Afrotropic, containing Trans-Saharan Africa (A historic term for what is now “Sub-Saharan Africa”), Madagascar and the Arabian Peninsula.
• Neotropic, containing South & Central America, South Florida, the Caribbean & the Falklands
• Australasia, containing Australia, Malaysia, New Zealand and neighbouring islands
• Indomalaya, containing Indian subcontinent, South East Asia, Southern China & the Indonesia islands he islands, Borneo, Java, Sulawesi and Sumatra (collectively the “Greater Sunda Islands”)
• Oceania, containing Polynesia (excluding New Zealand), Micronesia & the Fijian islands
• Antarctic, containing Antarctica, Alexander Island, South Georgia and the South Sandwich Islands.

These systems are based on the World Wildlife Fund (WWF) / “Global 200” biogeographic realms system and may also be called “ecozones” (“ecological zones”). Like Minecraft, a biogeographic region contains biomes, which describe the type of environment that an organism lives in. Biomes are shaped by the climate, and the same biome can be found in a different biogeographic realm. For example, low rainfall in the centre of Africa & Australia causes sparse vegetation which leads to open habitats which leads to deserts. A biome is not considered to be the same “ecozone”, as a biogeographic realm describes the evolutionary region from which those organisms originate rather than their choice of habitat.

Coleoptera, “Sheath-winged”: Beetles Have Hardened Forewings (“Elytra”) That Protect Their Delicate Hindwings

Beetles deserve their own article, perhaps even a textbook or three.

The largest insect order is Coleoptera some 390,000 described species (and counting) in ~500 families and subfamilies (also counting), grouped into four suborders (no need for counting):

• Archostemata, the ancestral beetles,
  • Their “basal” traits include complex wing venation, different elytral structures & variations in thorax anatomy (probably due to the two aforementioned differences).
  • There are more extinct than living species (“extant”) in this suborder.
• Myxophaga, the slime eaters,
  • Feed on algae, bacterial biofilms & other microbial films on submerged rocks and aquatic vegetation.
• Adephaga, the greedy eaters.
  • These are predatory beetles with voracious appetites – ground beetles, tiger beetles & diving beetles.
• Polyphaga, the many eaters.
  • 90% of beetles belong to this suborder. Their diverse mouthpart arrangements produces species that can consume wood, fungi, pollen, nectar, carrion, homework, leaves, seeds, dung, your mother’s low-salt cooking (“good for your blood pressure”), roots, stored grains and other insects.

The size of beetles goes from small (smaller than the small hive beetles in my beehives) to very large (the male Hercules beetles of the Neotropics). They all share the common feature of a “hard shell”, the elytra: heavily sclerotised, sometimes armoured and often compact. Compounds eyes are generally present (and sometimes very large), or absent in some species. The opposite is with ocelli, being generally absent (perhaps they do not need to sense polarised light as their flights are not long/far).

Another shared anatomical feature in beetles is in the size of their prothorax, which is large and extends past the coxae (the “first” or “basal” segment of an insect’s leg). The wings sit on the “pterothorax”, a fusion of the mesothorax & metathorax. The thickened forewings can be used in providing lift to help the beetle become airborne or be used as a hatch that opens and closes before and after flight respectively. Elytra assist in controlling water loss, as their sclerotisation covers the membranous hindwings & abdominal spiracles. Speaking of hindwings, they have extensive, complex pleating that enables the beetles to fold them beneath the elytra.

Beetle legs are variably developed (remember, hundreds of thousands of species) with variation in claws and adhesive structures. Some beetle legs are adapted for digging (“fossorial”), and others are modified for swimming (by possessing a thick fringe of hairs that helps them swim).

The Characteristics of Beetle Larvae Are Shaped by Their Niche

A common feature to beetle larvae is the sclerotized head capsule, opposable mandibles and thoracic legs (with five pairs [“segments”] being most common, although some can be legless). You can distinguish beetle larvae from that of moths & butterflies because beetles lack prolegs on the abdominal segment. Larval limbs can be campodeiform (having a protruding lower jaw & long thoracic legs), eruciform (grub-like with short legs) or scarabaeiform (also grub-like, with longer legs).

Many beetle larvae pupate in a purpose-built cell or chamber, rather than using silken cocoons. In the species that do produce cocoons, the silk is produced from the Malpighian tubules (found in the abdomen) or in exposed glands (as in the beetle family Coccinellids [ladybugs]).

Why Are There So Many Beetles?

If was to provide a short answer for how Coleoptera became so abundant and successful, I would tie it to their close relationship with plants, “co-evolving” with them as herbivores (e.g. Barraclough, Barclay & Vogler, 1998). Another possible explanation for their abundance can be attributed to the success of their diverse feeding habits and hardened forewings, enabling them to occupy many niches while maintaining protection from predators/parasites “in their league”. You can find beetles in freshwater, saltwater, intertidal (rocky shores, sandy shores, mudflats), fungi, dung, carrion, necrophages and above all, within every part of a plant⁴.

Such a close relationship with plants is sufficient to produce a large beetle variety, but the Coleopterans further diversified into carnivory, with families like Lampyridae (fireflies) and Coccinellidae (ladybugs). Predatory beetles have been used as biological control of aphids; you can buy ladybugs online and release them into your garden as a form of pest management⁵.

Strepsiptera, “Twisted Wings”: Male Stresipterans Have Twisted Hindwings; Most Females are Wingless

Strepsiptera is a holometabolous order of endoparasitiods (parasitoids are animals whose young develops inside the host, rather than external growth [as with the ectoparasitiod larvae of many wasps]). Males have large heads, bulging compounds eyes and no ocelli. Forewings are stubby and veinless, whereas he hindwings are broad, fan-shaped and twisted with a few radiating veins. Their legs are clawless and lack the second anatomical segment (“trochanter”, between the coxa & femur).

Females on the other hand look nothing like the males (“sexual dimorphism”), being wingless and larval-like in appearance, remaining in their “pharate” (hidden) state as an endoparasitoid⁶. Virgin females of most Strepsiptera protrude from their host’s cuticle, releasing pheromones that attract flying males who attempt to mate with her as she remains inside the host.

The first instar of Stepsipteran larvae is a “triungulin⁷ (“triungulid” for the nitpickers), it has three pairs of thoracic legs for mobility, however it lacks antennae or mandibles. The mobility is used to search for a new host. For example, in Stresipterans that parasitize Hymenopterans (bees, wasps), the larvae will sit and wait on flowers where they’ll latch onto a female (or male and then transfer onto a female), ride to the nest and then enter their host’s egg or larva.

The triungulid enters the host by enzymatically softening its cuticle, then moulting to its maggot-like second instar to begin development. Stresipterans are tiny, adults are several millimetres long, and the triungulid is perhaps < ~0.3 mm in length. Apart from two families, the larvae can be seen protruding from their host (with a microscope, most likely). The infested host is considered “stylopized”: they suffer morphological, physiological, and developmental abnormalities, but do not die, nor reproduce – they are hijacked by the parasitoid to further its growth, finally dying once the next generation of first-instar Stresiptera departs the female (Kathirithamby, 2009).

Mating in Strepsiptera: Traumatic Insemination Via Cephalothorax Punctures

Outside of the basal family Mengenillidae, female Strepsiptera have a simplified structure: they do not have legs, ovipositors, vagina, genital chambers ovarioles and other genital apparatus. Their eggs float freely within their bloodstream (haemolymph). A “brood organ” is used to release first instar larvae. The brood organ’s opening (termed “brood canal”) is at the cephalothorax (a fusion of the head of thorax), rather than the terminal end of the abdomen. Strepsipteran eggs hatch inside the mother (“ovoviviparity”) and the triungulids exist via the brood canal to seek out a new host.

In most Stresipterans, the female lacks proper reproductive anatomy, so the short-lived male make do by piercing her cephalothorax with his penis and thus inseminating her, a process termed “traumatic insemination”⁸.  This method developed as a way for males to bypass sperm competition with other males and avoid both pre- and post-copulatory female choice mechanisms (because the female decides who to mate with, and if someone she disapproves of was to mate with her, she can reject him or eject his sperm). Over evolutionary time, the disuse of female Strepsipteran reproductive organs led to their atrophy and eventually removal (see Peinert et al., 2016 in Stylops sp.).

Sexual competition does not stop there. Over time, males began competing for traumatic insemination of Stepsipteran females. Multiple traumatic matings would not be ideal for a long-and-prosperous life, so females probably responded to this pressure by developing an invagination within the cuticle of her cephalothorax. This “paragenital organ” could reduce the costs of traumatic insemination in Stylops sp. and aides the female in copulating without long-term harm (Peinert et al., 2016).

Diptera, “Two Wings”: Thousands of Fly Species Have Medical or Veterinary Importance

There are around 160,000 described species of flies in 150 families. Of those species, several thousand are relevant to mankind either medically or veterinary: mosquitoes, gnats, midges, house flies, and their relatives. An adult fly’s diet is mostly liquids, like nectar and honeydew from sap-sucking insects, or blood⁹ and other animal body fluids depending on the species. Some do not feed at all, living for briefly for the sake of reproduction.

A typical fly has a mobile head, large compound eyes and downward-directed mouthparts that (usually) form a proboscis for sucking. When the mouthparts are modified for biting, they become associated with blood feeding, as in sand flies and horse flies (speaking from experience). Flies have a one pair of wings on the mesothorax, with halteres (“balancers”) on the metathorax. Dipteran abdomens vary across species, with some having a reduced shape (as opposed to the typical eleven segments). Female flies lack a true ovipositor, instead developing a substitutional structure at the tip of their abdomen that they use to deposit eggs onto substrate.

Fly larvae lack true legs, and their head structure varies from a hardened capsule to acephaly (“a reduced head” with no external capsule, just an internal skeleton). Some larvae can have no moving mandibles and are said to be “obtect” (appendages glued to the body), or free and visible when pupating (“exarate”). Fly larvae can inhabit aquatic landscapes (as in mosquitoes) or terrestrial ones, depending on their feeding habit: phytophagy, predation, parasitisation or as an infestation of the living flesh of vertebrates (“myiasis”).

Sidenote: Zebras Developed Stripes in Response to Parasitisation From Flies

Many gen-pop animal behaviour books use zebras as examples of mimicry and deception, and they’re great to read. Some of the older texts state that zebras got their black and white stripes as a predator deterrence, as it makes it harder for a lion or other big cat to distinguish their target. However, lions (or hyenas) are both nocturnal and (relatively) short-sighted hunters; by the time one gets within striking range, the black and white stripes are of little use (I am told there are no streetlights in the savanna).

Tsetse flies (Glossina spp.) carry sleeping sickness (“Human African Trypanosomosis”) that affects humans and Nagana (Animal African Trypanosomosis), which affects cattle. Experiments on the tsetse flies found that they could readily land on a warm-blooded animal with a single-coloured coat (e.g. white, black or grey) but struggled to find a landing zone when the coat colours were horizontally alternating, as in the zebra’s stripes (Gibson, 1992). Further research from Caro and colleagues suggested that the stripy appearance of zebra was driven by constant biting from such flies, and that these patterns help deter ectoparasite attack (amongst other anti-predator signals; Caro et al., 2014).

Interlude: On The Process of Complete Metamorphosis

I did not plan on outlining the process of holometabolous metamorphosis as it deserves its own article; after all, it’s more complicated than “larva pupates into an adult form”. The changes are driven by hormones (ecdysteroids & high juvenile hormone-signalling), beginning with the programmed cell death of larval structures (muscles, salivary glands, portions of the gut etc..). The contents are recycled as nutrients, and the structures remain “undissolved” are reformed (e.g. nervous system).

The adult structures arise from imaginal discs, a progenitor-cell population that forms external structures like wings, legs, antennae, eyes and internal ones like the digestive tract, tracheal system, muscles and reproductive organs. For the neurons that are carried over from the larval stage, they may remove their larval connections and establish new adult circuits. The cuticle forms, and eventually the complete adult remains includes in the pupal cuticle (hence “pharate-” or “hidden-adult” stage).

Finally, the adult emerges (eclosion) by splitting the pupal cuticle and frees itself by contracting its muscles and abdomen. Beekeepers have seen that newbees (pun intended) are lighter in colour, soft, pale and unable to fly (as their cuticle has not yet hardened). Over the following minutes or hours (or days in honey bee workers), the cuticle hardens via sclerotisation (and sometimes melanisation), to produce the final colours and mechanical strength of the adult form, the imago, thus completing this (simplified) overview of the metamorphic process.

Mecoptera, “Long Wings”: Scorpionflies’ Etymology is Misleading, It’s Their “Beak” (Rostrum) That’s Long

Scorpionflies and snowfleas are an order of ~400 species in nine families. Their common names are derived from characteristics of the order’s three largest families: Bittacidae for hanging flies, Panorpidae for scorpionflies and Boreidae for the snowfleas. Species in these three families have an elongated rostrum, which is formed by the expansion of their mandibles and maxillae (themselves being slender and serrated).

Mecopterans have large, separated compound eyes and multisegmented antennae. Their two pairs of wings are narrow with a similar shape, size and venation. In snowfleas, the wings are reduced or absent, instead being used by males to grasp female snowfleas during copulation. The legs of some species may be modified for predation¹⁰. Male scorpionflies have an upward curve in the last few abdominal segments, giving them a scorpion-like tail (minus the sting, as these are their genitals).

Mecoptera have courtship rituals that begin with males attracting females via pheromones. To determine if intercourse can commence, the male provides her a gift of a meal offering (e.g. a captured insect). If the female deems the gift suitable and accepts it, she mates with the male while consuming the meal. This has led to instances of deception, with lesser males acting as females in order to secure a free lunch… Incentives, many such cases.

Mecopteran larvae have a sclerotized head capsule with mandibles and eyes. They have short legs with some prolegs, and are generally found in moist leaf litter, with variations between species. Larval diet varies, with some being detritivores, others scavengers or plant feeders. The adult diet varies from predatory to plant feeding.

Siphonaptera, “Tube Wings”: Fleas Are Dime A Dozen

All fleas are external parasites of birds and mammals (and those that infest birds trace their lineage to mammal-infesting ancestors; e.g. Zhu et al., 2015). There are some ~2,000 species across 18 families with shared characteristics of being wingless with mouthparts adapted for piercing and sucking (no mandibles, rather having serrated lances and needles [“stylet”]). As with parasitic lice, the compound eyes in fleas are absent, with ocelli ranging from none to well-developed ones. Their antennae lay in deep grooves, in order to protect it from damage as a result of contact with host hairs/scratching/biting and so on.

Siphonapteran cuticles have many backward-facing hairs and spines that can be grouped into combs, playing a role in defence from the host. “If you pick at me, I will prick you” sort of relationship. The three pairs of legs on fleas terminate in strong claws for grasping host hairs (or feathers), with the hind legs being elongated and powerful for making large leaps (One, two, three, me mother caught a flea…).

Unlike lice, flea larvae develop outside the host, within their nest (or under carpets, bedding, or cracks in floor surfaces for those that infest you and me). High temperature and humidity are required for optimal larval growth and pupation. Upon emergence from the pupa, the adult searches for a suitable host where it will spend its entire life.

Fleas Can Transmit Diseases When They Feed

Feeding is a bidirectional process: the flea sucks blood from the host, and in turn injects salvia into the affected area from its gut pump. This has the purpose of keeping the wound open and blood flowing, along with the unhappy side effect of transmitting microorganisms into the host’s bloodstream. This is not so much a concern in monoxenous (“single host”) species, instead being an issue with the polyxenous species that can live on several hosts. The plague fleas (Xenopsylla cheopis) belong to the latter category, having both rat and human hosts. This flexibility (or “lack of host specificity”) gives fleas a survival advantage over lice, as they can withstand separation from their host and live long enough to search for a new one.

Outside of the plague (itself caused by bacteria, Yersinia pestis), flea-transmitted diseases are of minor significance to human health (e.g. murine typhus or tularaemia; both easily managed with antibiotics). The greatest inconvenience from fleas are the allergic reactions that may occur from frequent bites.

Trichoptera, “Hair-winged”: Caddisflies Have Wings Covered in Fine Hairs

How do you distinguish a caddisfly from a moth? Look at its antennae – caddisflies have long ones, perhaps as long as their wings (or longer). If you can grab one and place it under a microscope, look at the wing veneration: caddisflies have anal veins (a region towards the ventral-proximal region) looped into the forewing and no discal cell (a region in the central wing area). When you get better at this, the final challenge will be to distinguish them based on the namesake: hairy wings (“Trichoptera”) versus the scaley wings of moths (“Lepidoptera” [the scales are modified hairs]).

The Trichoptera order has some 14,500 described species in 45 families with a worldwide distribution. Adults appear moth-like, whereas larvae are aquatic with five to seven instars. Larvae have a variety of feeding habits: predatory, filter-feeding, macrophyte-grazing (i.e. on aquatic plants) and detritivory. Adults drink nectar or water, but otherwise do not feed; they live short and mate quickly.

When it is time to pupate, A Caddisfly larva encases itself in a silken case¹¹ that is strengthened with materials from its environment: gravel, sand, twigs, plants, debris and so on. If you’re thinking “but this will make it harder for the adult to emerge” you should fear naught, for they have large mandibles that help them chew free off the cocoon. The pre-adult (pharate) pupa swims to the water surface, the pupal cuticle splits and serves as a platform for the adult to emerge and take flight.

Lepidoptera, “Scaled Wings”: A Butterfly Folds Its Wings Against One Another, A Moth Cannot.

The last two holometabolous entries are very popular. Lepidopterans is the order containing moths and butterflies. They are solitary species, mostly harmless (including the larval pests) and generally short-lived. Butterflies are almost-exclusively day flying, whereas moths are diurnal. There are moths than there are butterflies. The order contains some 160,000 species in over 120 families. Lepidoptera is further divided into four suborders, three of which contain few species that lack the characteristic long and coiled probiscis of the largest suborder, Glossata.

Adult lepidopterans range in size from very small, like the microlepidopterans, to rather-large, as with the emperor moths. The corresponding wingspan also varies, with species on the larger end of the spectrum being up to 30 cm long. Other than the probiscis (itself formed by elongated maxillary lobes [“galeae”]), the typical adult mouthparts have large labial palps, and nothing much else¹², since their diet is specifically liquid. The head has large compound eyes, with ocelli and/or chaetosemata (paired sensory organs on the top-lateral sides of the head) present.

An easy way to distinguish moths from butterflies is in how they hold their wings at rest: Butterflies have them folded together vertically, whereas moths hold them flat or wrapped around the body¹³. Another way to distinguish butterflies from moths is in the antennae, which is often arranged like the teeth of the comb (“pectinate”) whereas in butterflies it is knobbed or clubbed. Their mesothorax is large, which is where the wings sit. Wings are covered with a double layer of scales (themselves modified hairs called microtrichia) and both pairs are linked either with a frenulum (a fold of tissue), jugum (yoke) or simply overlapping. Lepidopteran legs are long and generally built for walking.

Mating, Feeding & The Larval Phase of Lepidopterans

Courtship in Lepidoptera involves both sexes releasing pheromones into the air, where they dance (or “compete”) until the mateship is accepted. Copulation occurs on the ground or on a perch, with the eggs being laid onto a suitable plant source. Laying locations can be atop a plant/leaf, close to it, or (for those with the modified ovipositor), directly into the plant tissue (seen in stalk-boring moths and some Yucca moths). Some species lay eggs in clusters, others individually. Not all eggs hatch right away; some may undergo diapause (“hibernation”) until the time is right.

To distinguish Lepidopteran larvae from that of beetles, look at their head capsule, mandibulate mouthparts, short antennae and five-segmented thoracic legs. In some species, a few abdominal segments have prolegs. The mouthparts have silk glands which they use for pupation. Moths produce a silken cocoon, whereas butterflies have a more “naked” covering (“chrysalis”). Some of the basal Lepidopteran species have pupa with exarate (recall: “free” or “detached”) appendages for mobility.

The larval diet is herbivorous, and exceptions exist as fungivores, predators or scavengers (wool moths being an example of the latter). For the few adults that feed, it is largely nectar, honeydew or seepages from live and decaying plants. To obtain proteins, Lepidopterans consume nitrogenous animal wastes (e.g. urine).

Spotting moths and butterflies is easy: they fly and many look pretty. Larvae not so much, they are built to be cryptic and camouflaged from their main visual predators, birds. If they are easily spotted, it is for aposematic reasons, for they display warning colours to warn predators that their bodies are toxic and unpalatable. These toxins are generally derived from their food by integrating plant metabolites, or produced internally as an anti-predator device.

Hymenoptera, “Married Wings”: The Wings of Ants, Bees & Wasps Are Joined Together by Hooks

My favourite taxa are the Hymenopterans. Bees are covered extensively throughout this website, with some mentions of ants and wasps. There is more though, as the 150,00 described species in this order are grouped into two suborders: Symphyta (the wood wasps and sawflies) and Apocrita (wasps, bees and ants). The stinging members of Apocrita are called “aculeates”.

Hymenoptera come in all shapes and sizes: small (e.g. Trichogrammitdae, endoparasitic wasps with < 1mm in length) to large (0.15 – 120mm, e.g. the Giant Asian Hornet Vespa mandarina or some female carpenter bees¹⁴). They can be slender, like the Ichneumonid wasps, or round and robust, like many bumble bees.

Mouthparts range from generalised mandibles to specialisations in sucking and chewing, or killing prey, corpse management, as well as defence and nest building. Compound eyes are large, ocelli may be present and the antennae is long and held forward-facing. Wings have reduced venation relative to other flying insects. “Hamuli” are hooks found in a row along the leading edge of the hindwing that couple with the hind margin of the forewing, thus “marrying” the two together. The ovipositor is used to lay eggs, and in the aculeates it is further modified into a sting with associated venom glands.

Endoparasitic Hymenopterans lay eggs that are deficient in yolk and may give rise to more than one larva (twins and beyond; “polyembryony”). Symphytan species have larvae that are largely phytophagous, laid amongst the foliage and wood where they feed; such larvae appear eruciform (caterpillar-like). By contrast, the Apocritian larvae is without feet (“apodous”) but possess strong mandibles for consuming pollen, prey or plant material. Adults feed on nectar, honeydew or the haemolymph of other insects (e.g. the parasitic wasp Eupelmus vuilleti); very rarely do adults prey on another insects, as shown by hornets in the family Vespidae.

The female Hymenopteran controls the sex of her offspring, laying an unfertilised egg for males and a fertilised one for females. This topic has been covered extensively with honey bees as an example in the article: “sex determination in honey bees”.

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Footnotes

1. You’ll hear “mandibulate” often as this is an umbrella term for mouthparts that are built for biting-chewing (e.g. prey, leaves) or for grasping (e.g. nest materials). The other mouthparts category is “haustellate”, which are for piercing-sucking (mosquitoes [blood], aphids & cicadas [plant saps]). All insect mouthparts have the same six components, arranged in different ways for different functions: Labrum (“upper lip”), Mandibles (“jaws”), Maxillae, Hypopharynx (a “tongue-like” structure), Labium (“lower lip”) & Epipharynx (“inner surface” of labrum). Which mouthpart style came first? Probably the mandibulates, as it is the “least specialised” feeding method. From this basal type came specialisation into various piercing-sucking methods (themselves split into subcategories like siphoning, sponging, rasping-sucking, cutting-sponging, & chewing-lapping). ↩︎
2. What does pollution mean to an insect? Insects are more sensitive to changes in the environment than fish because of their smaller size. Take Dobsonfly larvae as an example: fast-moving streams are rich in dissolved oxygen, which meets their metabolic demands for those long years of larval life. If organic matter (or sedimentation from human industries) is introduced, as in algal blooms, it will lead to bacterial decomposition that consumes dissolved oxygen, killing the larvae. There are also downstream effects (pun intended) of foodweb collapse, due to the death of the larvae’s prey species (nymphs of Mayflies/Stoneflies/Caddisflies and other aquatic insects). ↩︎
3. The marine realms are more variable, containing around 12-24 regions depending on your sources. They are based on the physical and land barriers, variations in water temperatures, salinity, precipitation, nutrient profiles etc. and the uniqueness of animal and plant species. A simplificated example: if a large family of fish is only found within 100km from the coast of Madagascar, then it becomes an ecozone. Venture 150 km out from the same coast, and you’ll find yourself in a different ecozone. ↩︎
4. There are beetles who feed on external structures like foliage, flowers, buds, stems, bark and roots, and there are the internal feeders, causing galls in plant tissues that look like bumpy outgrowths, or leaf miners that cause “squiggly white trails”. ↩︎
5. The quality of the live ladybugs is highly variable, and this may not be the fault of the manufacturer (grower?), as shipping, logistics, the day’s weather and your own care of the package prior to release influences their survival. ↩︎
6. The exceptions are found in the most basal (or “earliest”) Stepsipteran family, Mengenillidae, whose females have legs and are free living. Their target hosts are in the silverfish family Lepismatidae. ↩︎
7. The lifecycle of insects with highly mobile first instar (triunglins) followed by less-mobile subsequent instars is termed “hypermetamorphosis” – it’s almost as if they have three life stages, “triungulin” (or triungulid for my nitpickers), larva and adult. ↩︎
8. Traumatic insemination is when the mating partner is wounded via specialised organs (e.g. the penis). It likely evolved in response to high sperm competition between males, and akin to saying “Reproduce smarter, not harder”. Once inside the female, the sperm is stored (e.g. in the mesospermalege organ within the bed bugs Cimex lectularius), or inseminates eggs right away (as in our Strepsiptera). ↩︎
9. Unsolicited science trivia: Female mosquitoes (Anopheles spp.) only suck your blood when they’re looking to rear brood. ↩︎
10. Some species of scorpionflies dangle by their forelegs, leaving their enlarged hind legs free to capture prey. This is pretty unique considering that in other predatory insects it is the forelegs that are used for hunting (“raptorial”) whereas in Mecoptera it’s their hindlegs… The beekeeper in me would like to think of these as “prey baskets”, as opposed to “pollen baskets”. ↩︎
11. The appearance of Caddisfly pupal cases can be saddle-, purse- or tube-like, or it can be a free-living structure that’s akin to net spinning. ↩︎
12. Some Lepidopteran species may have primitive mandibles. ↩︎
13. It’s not that moths can’t fold their wings. After all, they share the same anatomy and wing musculature as butterflies. Instead, it’s a behavioural adaptation – the upright wing posture in butterflies helps with camouflage and thermoregulation during daylight hours, whereas most moths achieve better concealment by keeping their wings flat or roof-like against the substrate. Exceptions apply. ↩︎
14. Another large leafcutter bee is the Indonesian Wallace’s giant bee, Megachile pluto with a wingspan of 63.5 mm. ↩︎