Wasps

Wasps. The Astonishing Diversity of a Misunderstood Insect, by Eric R. Eaton, Princeton University Press, 2021.

The author has worked as an entomologist for institutions including the Smithsonian and is the lead author of the Kaufman Field Guide to Insects of North America amongst other claims to fame.

Who hasn’t been annoyed by wasps on a picnic or sat in a beer garden? Most people are hostile to them, some are very frightened of them. I have veered between batting them away and not reacting at all, even if one lands on my arm. I have never been stung. This book aims to correct our perceptions. I have rather put off reading it. How interesting could it possibly be? The answer is: very.

I’ve included a few photos of insects which are obviously not wasps simply because they have appeared whilst I was writing this post but this definitely is a wasp.

The illustrations are extraordinary. The book is not written as a tale but looks more like a field guide (but it’s much more than that) with plenty of infographics and some pretty densely scientific text, although Eaton is careful to ensure we understand the basics of, for example, evolution and taxonomy before pressing on. He includes welcome flashes of humour from time to time.

In terms of evolution, covered by the first section of the book, we think the creatures we call wasps today appeared a little less than 200 millions years ago, although there are fossil records of their ancestors. Bees and ants are, to massively oversimplify, basically wasps, at least they evolved from wasps. All three belong to the Hymenoptera order, “the first major branch of all insects that undergo complete metamorphosis (egg, larva, pupa, adult).” “Are Bees Just Hairy Wasps? Yes!”

The next section deals with anatomy. Wasps are of course invertebrates and arthropods. Insects are the only flying invertebrates. Already I am finding many “Ah, I see” moments here. Insects have open circulatory systems – blood bathes every organ within the body but their blood does not carry oxygen, that’s done by a network of tracheæ and then diffusion at a cellular level. Only the females have ‘stings’ and only in certain species.

Compound eyes sense motion better than we do but are not so good on detail. Antennae and other organs sense flavour and scent and vibrations. There are also ganglia which respond to stimuli independently from the brain. Variously shaped antennae are crucial and often constantly groomed, being used for locating mates (by the males), hosts for offspring (by the females) and inform of air currents, flight speed, smell, taste and more besides.

The complex structure of the thorax includes parts for oxygen intake and carbon dioxide output and is where the wing muscles are located. Except they aren’t really wing muscles as such, the thorax flexes and that is what causes the flapping, rotating and twisting movements. “Insects may be the strongest of all animals in proportion to their size, but they are strong because of their small stature, not in spite of it. Most insects have such little body mass that they require little muscle support.”

The abdomen – it is not easy to define where it begins since fused to the thorax – contains pretty much everything else including the infamous venom ducts and glands.

Those wasps which have wings generally have two pairs which hook together (with tiny hooks called hamuli) in flight at which they excel. Some can hover, others use their wings to row underwater. There is a great deal of variation in wing structure between species.

It’s when we move onto the ovipositor that it all starts to get a bit grim. These can be used to place eggs in substrate but it’s often a host larva, caterpillars or aphids, sometimes paralysed by venom as well as parasitised.

The sting is a sort of weaponised version of the ovipositor with the primary purpose of incapacitating, temporarily or permanently, hosts or prey. Bees’ stings are barbed and so cannot be withdrawn – not generally the case with wasps. They are also used in self-defence or defence of the colony. Some species have pseudo-stings – a deterrent.

Reminiscent of the Scoville scale which rates the spiciness of peppers, there is the Schmidt Sting Pain Scale which gives four levels, with four being the most painful. The descriptions Schmidt gives are rather wonderful. Level 1 might be “almost pleasant, a lover just bit your earlobe a little too hard”^[ or “light, ephemeral, almost fruity. A tiny spark has singed a single hair on your arm.”

At Level 2 we have “the debilitating pain of a migraine contained in the tip of your finger”, “hot and smoky, almost irreverent. Imagine W.C. Fields extinguishing a cigar on your tongue.” The sting of the honeybee is described as a similar feeling to “The oven mitt had a hole in it when you pulled the cookies out of the oven.”

Level 3: “After eight unrelenting hours of drilling into that ingrown toenail, you find the drill wedged into the toe.”

Level 4:  “Paraponera clavata stings induced immediate, excruciating pain and numbness to pencil-point pressure, as well as trembling in the form of a totally uncontrollable urge to shake the affected part.” He described the sting as “pure, intense, brilliant pain…like walking over flaming charcoal with a three-inch nail embedded in your heel.” Schmidt later gave the sting of a tarantula hawk species, Pepsis grossa , a rating of a 4, which he described as “blinding, fierce [and] shockingly electric” and of another species: “Torture. You are chained in the flow of an active volcano. Why did I start this list?”

It also reminds me a little of the whimsy of the Beaufort Scale.

The author returns to the list and the Pepsis sting later on, explaining that although the pain is excruciating for several minutes, there is no nerve or tissue damage or any other sub-lethal or chronic effect.

Wasps are sexually dimorphic. For some species we only know the females – they may use parthogenesis or it may just be that we haven’t identified the males yet.

There are some bizarre variations – spikes, hooks, horns and so on, some of unknown function, some of which serve as weapons or for digging. One family, the Dryinid, have complex scisssor-like extensions, “a marvel of evolutionary engineering”.

Not a wasp. A Forest Bug or Red-legged Shieldbug.

Wasps are essential pollinators and controllers of other insects which damage crops, scavengers and useful decomposers of dead wood, but some of the detail about their lives is far from endearing. Various insects serve as hosts for various kinds of dryinids. “The dryinid larva that hatches from the [implanted] egg develops initially as an internal parasite, but as it grows it eventually bursts the seams of its host, its hindquarters oozing between the host’s body segments.” Nice.

There is a very helpful glossary at the end of the book. A parasite is an organism “that requires another organism as a host, and feeds and grows without killing the host.” A parasitoid however is a parasite that invariably kills its host. Then there are hyperparasitoids, a parasitoid of a parasitoid.

The life cycle of the wasp – egg, larva, pupa, adult – has evolved so that each stage can be dedicated to particular functions and/or better survive in conditions hostile to a different stage of growth. Sex is determined at birth: fertilised eggs become females, unfertilised eggs become males. So, females have two sets of chromosomes, males only one: “haplodiploidy, a puzzling attribute that continues to confound entomologists.”

There are various strategies for egg laying but four families of Hymenoptera “are able to inject a single egg into a host and then have the embryo split into many more: upwards of 2,000 additional embryos in some cases.”

“Instar” is a favourite word for crossword compilers. I knew only that it was something to do with insect development, but now I know that it refers specifically to the intervals between moults of insect larvae. The job of the larva is to feed and grow.

The nests of Paper Wasps are architectural wonders. Most wasp species are solitary but these are not. I thought this section might give respite from the gruesome, but no. The dominant female of those who reproduce “suppresses the development of functional ovaries in her daughters” and bullies them into raising her offspring.

The pupa stage may take place inside a nest, a gall, a plant stem or a cocoon and may involve going into a state of torpor over winter. This is when the process of becoming an adult happens. It is a phase of reorganisation. After this, it’s all about feeding, mating and finding hosts.

Certain gall wasps practice heterogony: “a life cycle of alternating generations between a traditional sexual generation involving makes and females, and an asexual generation of females that reproduce without males via parthenogenesis.” The genetic origins of this are unknown. There seems no end to the complex wonders of wasps.

The fourth section, ‘Beauty, Purpose Expressed in Structural Design’, has especially stunning photographs, the colours, often metallic, and patterns, often serving to warn or camouflage. The pretty Jewel Wasp is a kleptoparasitoid, developing on food intended for the host by the host’s parents. Brilliantly blue/green Cuckoo Wasps are kleptoparasitical in the nests of other solitary wasps or bees. But we do not know the purpose of some of the amazing colours.

Wasps are the only pollinators of some plants, especially orchids. Consequently the Mirror Orchid not only looks a bit like a female scoliid wasp but also mimics her fragrance to attract males.

There are some symbiotic, mutualistic relationships with wasps where both species benefit, including with mites, fungi, viruses and bacteria. But the Voodoo Wasp (amongst others) lays not just eggs but a virus in the host, such as a caterpillar.

I had wrongly assumed that plant galls were a sort of tumour, an indication of poor plant health, but when they are the result of egg-laying, they are the plant’s response involving “channelling more nutrients to the site … creating a swelling that serves as home and food for the larval occupant.”

We simply don’t know how many species of wasps there are. There are many different answers given online (30,000, 150,000). All we know (somehow) is that most species remain to be discovered. But “scientific estimates conclude that there are between 833,000 and 1.1. million species of parasitoid Hymenoptera, the bulk of which are ‘micro Hymenoptera’ “. There are thought to be some 9,000 species of wasp in the UK and tens of thousands worldwide.

We learn of Micro- and Macro-parasitoids. I am not sure whether this falls into the latter category but this dead wasp coincidentally appeared on my notepad whilst I was writing. I couldn’t get a decent photo and by the time I had found my digital microscope and then remembered how to use it, a puff of air had taken it away. It definitely has black and yellow bands and measured just 6mm in length.

Then the 220 species of pollen-eating wasps, stinging parasitoids, and cicada killers. I love the sound of cicadas and so was surprised that the author finds it migraine inducing and annoying. Cicada killers are one of many examples to show extraordinary strength, capable of flying with or dragging victims back to their underground burrows.

Hyperparasitism remains a mystery to us in terms of its evolution. Not all species are obligate hyperparasitoids, some can be ‘just’ parasitoids too. Some feed from the inside of their hosts, endoparasitoids, or from without, ectoparasitoids.

Yet another category: inquilines. They reside in the living quarters of other organisms bringing neither benefit nor harm. Relatively benign then. Others engage in hostile takeovers.

The social wasps are the ones that annoy us, the ones which sting and raid our picnics and barbecues. A wasp colony is matriarchal, ruled by aggression. Some colonies consist of tens of thousands of individuals. They feed protein to their larvae but, remarkably, the larvae feed the adults too by producing a nutritious fluid. This mutual feeding is known as trophallaxis. The paper nests can be very strong and other animals including birds can take advantage by living nearby, finding protection themselves from the vigour with wasps defend their nests. Social wasps may cool the nests by fanning their wings and after rain remove water, drop by drop.

There are moreover nocturnal wasps, with, unsurprisingly, rather different eye structures. There is even a species, Apoica pallens, the moon wasp, which is most active during a full moon.

The seventh section of the book deals with wasp behaviours. Hosts are not always found by sight – chemical cues, scents, are often the main attraction. There are ingenious strategies to deal with intense heat and cold. It’s not just nectar they rely on to feed – some species cannibalise their young when food is scarce, which has the added advantage of reducing the numbers they need to nourish. It’s pretty much only the females which look after their offspring – males have been observed feeding their sisters but paternal care is almost non-existent.

Vibrational sounding, akin to the echolocation used by bats, is another tool for some wasps. Buzzing comes from the wing muscles and may be used to deter predators and competitors.

Warrior wasps are properly ferocious. They respond to threats by drumming synchronously before they emerge en masse to deliver their stinging assaults. Other subjects covered here include sleeping, courtship, nesting and mating. Some elaborate nests are inarguably beautiful.

Section 8 is all about those creatures who mimic wasps, visually and through their behaviour. These include flies, beetles, true bugs, moths, katydids and mantidflies. The mimicry is sometimes so good that it “can cause even the most experiences entomologist to do a double-take.”

Neither a wasp nor a wasp mimic, but this I found this Pale Mottled Willow Moth on my computer screen one recent morning.

Next we are reminded that wasps are not invincible. Predators include birds, reptiles, other invertebrates and mammals but other wasps can represent the worst threats, along with parasites, viruses, fungi and pathogens.

Before a concluding guide to the most commonly encountered wasps of the world, the author turns his attention to their relationship with humans. They can be our allies, feature in religion and mythology, folklore and superstition, history, tradition, pop culture, literature, art and entertainment. Eaton looks at all of these with typically forensic precision. Lewis Carroll’s ‘The Wasp in a Wig’ was suppressed from Through the Looking-Glass because the illustrator, John Tenniel, refused to depict it.

Fear them, loathe them or admire them we are left in little doubt that the world needs wasps.