Insects
What would be left of our tragedies if an insect were to present us his? ~ Romanian philosopher Emile Cioran
Insects comprise over half of all animal species. Before the onset of the mass extinction event caused by men, insect populations were prolific.
One in every two animals is an insect. ~ Australian entomologist David Yeates
There are 10 million different insects. Of that assemblage, only 2% are eusocial.
Insects have a hard exoskeleton made of chitin microfibers surrounded by protein matrices which vary by insect. Exoskeletons are layered, analogous to skin. The outer layers block foreign matter from entering, protect from abrasion, and reduce water loss. Skeletal muscles attach to the innermost layer.
Despite their small body size, insects have many more muscles than vertebrates, as the exoskeleton provides proportionately greater surface area for muscle attachment.
The strength of exoskeletons is impressive. The skinny neck of an ant can withstand 5,000 times the ant’s body weight.
Insect bodies have a tripartite segmentation: a head, thorax, and abdomen. The head houses compound eyes, 2 antennae, and mouthparts. The thorax bears wings, if wings are present. The abdomen holds the digestive system.
Insects have 6 legs (hexapods), while arachnids (e.g., spiders) sport 8 legs (octopods).
Reflecting their vast variety of diets, the mouthparts of insects vary enormously. Adaptively, this part of an insect is the most variable.
Antennae are an essential sensory organ. In flight, flies’ antennae keep them on course in the face of a breeze.
Tiger beetles scurry after prey so fast that they run blind. Antennae keep constant alert for obstacles. The beetles nonetheless must periodically stop for milliseconds to relocate prey.
Honeybees use their right antenna to distinguish between compadres and strangers. Their left antenna is more smell sensitive and plays a key role in communication.
In evolutionary time, insects are the earliest known eusocial creatures. Honeybees, weaver ants, leafcutter ants, and termites are exemplary eusocial insects. By contrast, Hymenopteran insects are presocial. Hymenoptera is the insect order which includes wasps, sawflies, and some early-evolved ants and bees.
Metamorphosis
Metamorphosis is the physical process which animals undergo during development. There are 3 types of metamorphosis: ametabolous, hemimetabolous, and holometabolous.
Ametabolous development is simply a gradual size increase until adult dimensions are attained. Such growth occurs in silverfish, springtail, and other primitive insects.
In later-evolved insects, such as grasshoppers, termites, and true bugs, gradual, or hemimetabolous, metamorphosis transpires. The hemimetabolous life cycle is: egg, nymph, and adult. A nymph, or immature insect, roughly resembles an adult in form and eating habits, but differs in body proportions, size, and coloring. Visible rudimentary wings develop externally. Development gradually occurs, involving a series of molts (periodic shedding of the outer skeleton). An adult emerges after the final molt.
The most dramatic metamorphosis is holometabolous: egg, larva, pupa, adult; occurring in beetles, butterflies, moths, flies, wasps, and bees. Larvae are wormlike grubs which pupate to transform into adults. The pupal stage is immobile and nonfeeding. Wings develop externally as larval organs and tissues are replaced with adult structures during pupation.
Wings
Insects are the only invertebrates that evolved flight. Our understanding of their remarkable flight abilities remains incomplete.
Insect wings are outgrowths of the exoskeleton. There are commonly 2 pairs: the forewings and hindwings, though a few insects lack hindwings.
In some species, only 1 sex has wings; typically, the male. Velvet ants and twisted-wing parasites (Strepsiptera) are exemplary.
Strepsipterans are endoparasites of other insects, including bees, wasps, leafhoppers, cockroaches, and silverfish. Virgin females stay within the host upon hatching, drawing flying males to them by a pheromone locator.
In some eusocial species, such as ants and termites, flight is selective. Workers don’t have wings.
Wings may be produced only at a certain time in the life cycle. Aphids wing it only during a dispersal phase.
Insects wings are cuticles made from chitin: the 2nd-most common natural material due to its toughness. Grasshopper legs are also chitin cuticles. For their weight, grasshopper legs are one of the sturdiest organic constructions known.
The cuticle membranes of insect wings are not so tough. They are instead subject to cracking. Yet grasshoppers and locust fly for days, over deserts and oceans, on wings 10 times thinner than a human hair. The wings withstand hundreds of thousands of beats.
The wings do crack at spots, but the cracks are contained by veins that crisscross each wing, segmenting a wing into hundreds of pieces. Veins that act as crack barriers increase wing durability by 50%.
Wing veins are heavier than the cuticle membrane. There is a mathematically ideal ratio between the protection that veins provide versus the additional weight they impose. Insect wings possess the optimal trade-off between lightweight cuticle membrane segments and vein patterning. Insect wings are a miraculously ideal adaptation.
Insect wings start as living tissue. During maturation into adulthood the cells between the strut work of wing veins die. The dried-out zones may become cellophane-clear or take on coloration; bordered by the vein network, wings may look like stained glass in a cathedral window. How that happens has been mysterious until quite recently.
It was long thought adult insect wings were themselves simply structural cells; as alive as toenails. But they are instead living, breathing appendages. Wing veins have their own respiratory tubes, nerves, and such.
Morpho Dragonflies
Morpho dragonflies of South America have wings that are a shimmering blue. There is no blue pigment on these wings. Instead, oxygen captured in the respiratory tubes of the wings creates the lustrous blue. How that happens involves quite complex physics. Nanoscale spheres on the wings are sandwiched between blankets of black pigment-filled nanolayers. This setup enhances blue light reflections off the veins, while stifling other wavelengths. That is not all. On top are 2 more nanolayers, each made of wax crystals shaped like little leaves, which play tricks with the light to further the blue.
The blue of morpho dragonfly wings is an honest signal of health, which helps to intimidate rivals for the best territory for mating opportunities. Beyond the bright blue wings, there is no courtship display for these dragonflies. A female flies in to inspect a true-blue male and he grabs her.
Feet
While wings are striking for granting the power of flight, feet are not so facilely impressive. But the workings of insect tarsi are practically as important as their ability to flutter and fly.
Many insects leave lipid footprints. These may help adhere to a smooth surface and serve in prey capture and predator defense. Beetles notably appreciate sticky feet for these reasons.
Telltale tarsal marks may be as much for remembrance of past action as they are for traction. Ants navigate to found food stores and make their way back to the nest partly upon the scent that their footprints leave.
Smelly feet are salient to foraging bees. Scent marks tell a bee how recently the nectar of a flower has been harvested, signaling whether lingering is worthwhile.
Bees can also tell by scent mark who visited: a family member or stranger. Such intel can be critical in determining the potential productivity of a flowerbed. A field lousy with competition indicates that an abundance of blooms is not necessarily the sweet smell of success.
There is a nefarious side to the scent marks of bee feet. Socially parasitic cuckoo bumblebees use the smell of footprints to recognize their potential host. Their own cuticle hydrocarbons mimic those of those bees whose homes they aim to invade, thus allowing these homewreckers to enter unannounced.
Fairyflies
The fairy wasp is the smallest insect in the world: a mere 0.5 to 1.0 mm long. Life as well is short: but a day or 2, though access to food may stay the grim reaper for a little while. The longest-lived fairfly species last 3 to 11 days.
Fairyflies live in temperate and tropical regions throughout the world, from desert to rainforest, but are seldom noticed by people. At least 5 species are aquatic, living above freshwater ponds and streams.
Mating is a brief encounter, without courting behaviors, between a single male and female. No interest by either party lies past that. The females of some species can reproduce without males.
All fairy wasps are parasitoids of the eggs of other insects, which are commonly laid in places concealed, such as plant tissues or underground. A fertile female searches for suitable host eggs by tapping antennae over the stems and barks of plants, looking for a telltale scar left by another insect’s boring and egg-laying.
Once a candidate egg nest is found, a fairy wasp inserts her antennae into the recess to sense the suitability of the eggs. Having found a clutch of apposite victims, a fairyfly places her eggs inside the host’s eggs with her ovipositor, feeling her way with her antennae. The implanted host eggs become nourishment for developing fairyfly larvae, which rapidly emerge.
Fairyflies are typically solitary, but sometimes gregarious in encounters with each other. Though short-lived, their behaviors are similar in sophistication to related asocial wasps (chalcid wasps).
The fairy wasp brain is remarkably tiny too. Fairyflies shed much of their neural network in reaching adulthood, with the simplest of neurons, over 95% of which lack a nucleus. It makes one wonder where fairies store their smarts; surely not in any physical substrate.
Dragonflies
Dragonflies are the fiercest predator in the insect world and the most successful hunter of all animals. Lions are lucky to catch 1/4th of the prey they pursue. Half of the hunts by a great white shark end empty mouthed. In contrast, a dragonfly taps its target over 97% of the time.
A dragonfly commonly consumes its catches on the fly, not bothering to alight. A meal is munched while looking out for the next. Dragonflies are voracious.
Dragonflies eat other flying insects: mosquitoes, flies, bees, and wasps, though vary rarely butterflies. In a pinch, ants are sometimes snatched. In turn, dragonflies are preyed upon by larger dragonflies, spiders, birds, lizards, frogs, and water bugs.
A dragonfly can selectively focus on a single prey amid a fluttering cloud of other insects. A dragonfly tracks its target, constantly calculating intercept trajectory while adjusting for changes. It has a mental model of its body flying through geometric space to precisely rotate and align with its prey’s flight path.
At the end of the chase, the dragonfly makes a basket out its legs and the prey drops into it. ~ American zoologist Anthony Leonardo
A dragonfly can even keep 2 targets in mind: switching from one to the other opportunistically. This multitasking indicates working memory and high-order thinking comparable to the most intelligent animal species.
Dragonflies on the hunt perform internal calculations every bit as complex as those of a ballet dancer. ~ Anthony Leonardo
Dragonflies are ambush predators. A dragonfly attacks from behind and below, so that its prey remains unaware of its impending doom.
Dragonflies are adept aerialists: able to hover, dive, fly upside down and backward, pivot 360° in 3 tiny wing beats, and zip through the air at 48 kilometers per hour: the fastest insect flier.
The wings of many insects move largely as a unit, by flexing the entire thorax. A dragonfly has 4 ultraflexible wings attached to the thorax via independent muscles. This allows each wing to be maneuvered independently.
The result is unparalleled aerial ability. Only hummingbirds are comparable. Unlike a hummingbird, a dragonfly can be missing an entire wing and still capture prey.
Dragonfly visual acuity matches aerial agility. With 30,000 ommatidia (photoreceptors units) in each of its complex eyes, vision is all around all the time.
Dragonflies have tetrachromatic vision: red, green, blue, and ultraviolet. They also see polarization, which affords even greater vision faculty.
Dragonflies may use different opsins at different ages, to optimize their vision to their environment. The larvae of some species that hatch in sand may lack blue opsins, as blue light does not easily reach them.
There are trade-offs to the extraordinary processing demands of dragonfly flight and sight. Dragonflies are practically deaf, and their stubby antennae don’t smell very well.
Dragonflies are not a very differentiated group. There are only 7,000 species worldwide; contrasted to hundreds of thousands of beetles and butterflies. Like sharks, dragonflies’ striking success merits modest speciation.
Cockroaches
Both the cockroach and the bird would get along very well without us, although the cockroach would miss us most. ~ American naturalist Joseph Wood Krutch
A cockroach may live a year of more. 75% of a roach’s life is in development: going through a series of nymphal stages, becoming more adult with each step.
Cockroaches of all ages live communally near food and shelter. Adult females often cluster together socially to keep unwanted male suitors at bay.
Some cockroach species incubate their eggs internally, bearing live young that stay in contact their mother for hours after birth. The close contact may be critical for survival, as newborn cockroaches are extremely vulnerable to cannibalism. And young cockroaches pick up nutrients from mom. Cockroach mothers are conscientious.
Catching a cockroach isn’t easy, even for toads, their natural predators. Just before a toad unfurls its lightning-fast tongue to snag a roach, the insect has already turned and started to dash to safety.
Cockroaches may be psychic, but there is a more tangible explanation. A roach has wind-sensitive hairs on its cerci: the paired whisker-like appendages protruding from the rear of its abdomen. The smallest gust tells a cockroach that something is astir, and from which direction.
Roaches are acrobatic escape artists. Upon reaching the edge of a hiding place that offers an underside, a cockroach grips the edge with hook-like claws on its rear legs, and swings 180° to land firmly underneath, upside down. A roach can pull off this maneuver in 1/5th of a second; faster than any pursuer can follow.
Keeping a low profile is essential to cockroach survival. These furtive creatures prefer the dark and have adapted to it with a keen sense of smell. Just as we make mental maps based upon sight, cockroaches mentally map via olfaction, creating cerebral smellscapes.
Cockroaches have lived with hominids at least as long as the hairless apes took to sleeping in caves, where roaches resided before they had homes built for them.
The 4 most common cockroaches in the US arrived with immigrants. The abundant German cockroach came with the earliest waves of Europeans coming to the New World. The larger American cockroach arrived on slave ships from Africa.
Individuals and their personalities matter. ~ French ethologist Odile Petit
Each cockroach has its own personality. Cockroaches are gregarious. Colonies make collective decisions via personality-driven group dynamics.
Once they move in, they don’t leave. ~ American ethologist Mark Stoeckle
Roaches are reluctant to relocate. Once infested they feel invested. This is evidenced by local populations belonging to the same gene pool. On the Upper West Side of New York City, 80% of the American roach residents there are related. On Roosevelt Island, it is 90%.
Other Insect Families/Clades
