Evolutionary dead ends

By Athayde Tonhasca

In 1842, the Darwin family – Charles, his wife Emma, and their two children William and Anne – moved to Down House in the village of Downe, England. The Darwin patriarch, who had travelled the world aboard H.M.S. Beagle (1831–1836), would spend the remaining 40 years of his life in quiet isolation at home because of ill-health. Darwin’s condition (whose origin still puzzles scholars) did not slow him down; he embarked on several projects such as monographs on coral reefs and barnacles, and of course overseeing the publication of On the Origin of Species. But Darwin spent most of his time working with plants, which are convenient study subjects for someone with a sedentary life-style. Assisted by gardeners and occasionally his children, Darwin observed and experimented with cabbage, foxglove, hibiscus, orchids, peas, tobacco, violets and many other species in his garden and glasshouse.

Darwin’s glasshouse at Down House, where he conducted many experiments © Tony Corsini, Wikimedia Commons.

Among various major contributions to botany (detailed by Barrett, 2010), Darwin documented the importance of cross-fertilisation (i.e., the transfer of pollen between different plants) for producing healthy offspring. Darwin, ever meticulous about supporting his theories with data, amassed eleven years of continuous observations to highlight the superiority of cross-fertilisation over self-fertilisation, i.e., the transfer of pollen within the same flower or between different flowers on the same plant. 

Methods of transferring pollen from the male anthers to the female stigma © Bartz/Stockmar/Ziyal – Insect Atlas, Wikimedia Commons.

Indeed, the great majority of flowering plants predominantly or exclusively outcross – that is, they mate with other individuals – even though they could easily self-fertilise because they are hermaphroditic (their flowers contain both male and female sexual organs). In fact, numerous flowers have mechanisms to avoid self-fertilisation. At best, many self-pollinated species (or ‘selfers’) exhibit mixed mating systems.

The bee orchid (Ophrys apifera). Despite its name, this orchid is mostly a selfer in northern Europe. In the Mediterranean, where this orchid is more abundant, its flowers are pollinated by bees © Bernard Dupont, Wikimedia Commons.

Self-pollination has some advantages: it helps to preserve desirable parental characteristics when a plant is well adapted to its environment. Because selfers do not depend on pollen carriers, they can colonise new habitats with a handful of individuals. Selfers do not have to spend energy on nectar, scents, or substantial quantities of pollen. Self-pollination is useful to farmers, as the genetic identity of a variety or cultivar is easily maintained, without requiring repeated selection of desirable features.

Comparing self-fertilised and crossed seedlings of common toadflax (Linaria vulgaris) in his garden prompted Darwin to investigate the effects of cross-fertilisation (Thompson, 2018) © Tony Atkin, Wikimedia Commons.

Self-pollination sounds like a convenient and rational lifestyle, but there are catches, and they are considerable. Selfers’ limited genetic variability makes them vulnerable to environmental changes; a hitherto well-adapted population can be driven to extinction if no individuals are adapted to novel conditions – and changes are inevitable, given enough time. Selfers are also particularly susceptible to inbreeding depression; if the population is homogeneous, genetic defects cannot be weeded out by genetic recombination.

Taking into consideration the long-term hazards of selfing, it seems paradoxical that 10 to 15% of all flowering plants from many taxonomic groups made the transition from outcrossing to full self-fertilisation. Darwin proposed an explanation for this puzzle: cross-pollinated species would turn to self-fertilisation when pollinators or potential mates become scarce. In other words, self-fertilisation assures survival when outcrossing becomes inviable. Darwin’s hypothesis, currently known as the ‘reproductive assurance hypothesis’, continues to be the most accepted explanation for the evolution of self-fertilisation.

Remarkably, researchers were able to quickly induce the transition from cross-pollination to self-pollination in the common large monkey flower (Erythranthe guttata, previously known as Mimulus guttatus) by preventing plants’ contact with pollinators (e.g., Busch et al., 2022). Monkey flowers kept in a glasshouse with no pollinators for five generations increased the production of selfing seeds and showed a reduction in the stigma to anther distance – this feature, known as herkogamy, is one of the indicators of ‘selfing syndrome’: the greater the distance between stigma and anther, the greater the likelihood of the stigma receiving external pollen, thus the lower the chance of self-pollination. After nine generations, plants experienced a significant reduction of genetic variability. Monkey flowers kept in another glasshouse with free access to the common eastern bumble bee (Bombus impatiens), one of the plant’s main pollinators, underwent none of these changes.

L: The common large monkey flower, a native to western North America. Its wide corolla and landing platform are convenient for its main pollinators, bumble bees © Rosser1954, Wikimedia Commons. R: Diagram of a large monkey flower with the upper corolla removed to show the reproductive structures © Bodbyl-Roels & Kelly, 2011.
A common eastern bumble bee; its absence induces selfing in large monkey flowers © U.S. Geological Survey Bee Inventory and Monitoring Lab.

What do these observations of the monkey flower tell us? For one thing, they are cautionary tales about the risk of losing pollinators. A variety of human disturbances such as agriculture intensification, loss of habitats and diseases have caused a decline of some insect populations, including pollinators. A scarcity of flower visitors may threaten pollination services directly, or induce some plants to adapt quickly and become self-pollinated. Adaptation sounds good, but selfers’ lower genetic diversity and reduced capacity to adjust to environmental vicissitudes make them vulnerable to extinction.

The renowned botanist and geneticist G. Ledyard Stebbins (1906-2000) suggested that selfing is an evolutionary dead end: it is advantageous in the short term but harmful in the long run. And because the transition from outcrossing to selfing is irreversible, according to Dollo’s Law (structures that are lost are unlikely to be regained in the same form in which they existed in their ancestors), self-fertilization ends up in irretrievable tears. And the monkey flower has shown that it all may happen before we notice it.  

Loss of pollinators could be the end of the line for plant species forced into self-pollination © Vaikoovery, Wikimedia Commons.

Just can’t wait to get on the road again

By Athayde Tonhasca

The publication of On the Origin of Species is 1859 is unquestionably one of the most significant episodes in the history of science. Charles Darwin’s and Alfred Russel Wallace’s theory of evolution by natural selection caused such a commotion that one of the book’s other idea didn’t get much attention at the time of publication. For one thing, Darwin dedicated a little over one page to it: the suggestion that evolution is not always the product of a struggle for existence, but sometimes is driven by sexual selection. Or, in Darwin’s own words, by ‘a struggle between the males for possession of the females’.

Darwin was stumped by the fact that natural selection could not explain obvious differences between males (producers of many small reproductive cells or gametes – the sperm) and females (producers of fewer, larger gametes – the eggs) of many creatures. Why should it be that male lions have manes, male deer sport massive antlers, many male birds are endowed with bright and colourful plumage, while their female counterparts have none or subdued versions of those features? Even worse, some characteristics appear to hinder survival and thus cannot be explained by natural selection. Darwin vented his vexation in a letter to American botanist Asa Gray: ‘the sight of a Peacock’s train whenever I gaze at it makes me sick’.

This Indian peafowl’s (Pavo cristatus) covert feathers (its train) would be tricky if the bird is chased by a tiger in their native Indian forest © Paul Lakin, Wikimedia Commons.

But Darwin’s aggravation didn’t last long, as he elaborated the theory of sexual selection in a subsequent book: The Descent of Man, and Selection in Relation to Sex (1871). In it, he suggested that features in some individuals (males or females) give them advantages over individuals of the same sex solely in respect of reproduction, even though these features could be harmful in other circumstances. Sexual selection operates from differences in mating success, whereas natural selection results from variability in other fitness traits. For psychologist Geoffrey Miller, ‘natural selection is about living long enough to reproduce; sexual selection is about convincing others to mate with you’.

In The Descent of Man, Darwin wanted to provide evidence that evolutionary principles – including sexual selection – apply to humans. This cartoon from Fun magazine (1872) mocks his ideas. The caption reads: That Troubles Our Monkey Again – female descendant of Marine Ascidian: “Darwin, say what you like about man; but I wish you would leave my emotions alone“. 

Sexual selection would work in two ways: through direct competition between males (or less commonly between females), so that contestants become larger and acquire showy ornaments or weaponry, or by female choice (or less commonly by male choice), where mates are picked based on their perceived quality as parental material. In the case of peacocks, a female would choose a male with the most flamboyant train, which indicates vitality, health, survival skills, and so on. And by showing off his colourful appendage, the male signals to the female that her offspring would have a better chance of survival if he was their daddy.

A figure from The Descent of Man, depicting a male (top) and a female of the suitably named Atlas beetle (Chalcosoma atlas).

For Darwin, morphological differences between males and females (sexual dimorphism) are the expected consequences of sexual selection. Since then, evidence has suggested that natural selection can also lead to sexual dimorphism; for example for some birds, differences between males and females in bill morphologies appear to be the result of dissimilar foraging habits (e.g., Tomotani et al., 2022). The current view is that sexual dimorphisms, expressed as differences in appearance, internal morphology and biological functions, are the result of all selective pressures – natural selection and sexual selection – on males and females.

For many invertebrates, females are larger than males, possibly because females need to produce lots of eggs and defend their brood; for birds and mammals, size is biased towards males, a likely result of intra-male competition. L: Female (left) and male banana spiders (Argiope appensa) © Sanba38; R: A male northern elephant seal (Mirounga angustirostris) towering over a female and a pup © Mike Baird, Wikimedia Commons.

Sexual dimorphism is one of the most pervasive traits in some plants and many animals, and its consequences are far and wide. For us humans, besides the obvious dissimilarities in size, muscle mass and fat distribution, men and women differ in the risk of contracting some diseases, absorption of drugs, response to therapies and vaccination, and so on. That’s why health researchers are increasingly being required to distinguish the sex of their subjects in clinical trials (e.g., Willingham, 2022).

Naturally, sexual dimorphism is found in bees as well, and it is manifested primarily in their haplodiploid system of sex determination, where unfertilized eggs result in males and fertilized eggs result in females. But bee dimorphism is also expressed in a range of traits such as body size, morphology, coloration, physiology and behaviour, all attributes linked to the roles played by each sex for the species’ survival. Females take care of nest construction and brood provision; in the case of social species such as honey bees (Apis spp.) and bumble bees (Bombus spp.), they maintain and defend the nest. Males on the other hand are driven by one main objective: to seek females and mate with them. So they have no pollen-carrying structures or stingers. This rather narrow life plan has not helped the reputation of males, which have been labelled lazy, free-loading sperm donors. But drones (male honey bees) help with maintaining a hive in good order, and males of many species are better pollinators then their female counterparts.

Hind legs of a male (L) and a female bee, which has a scopa – a cluster of stiff hairs to harvest pollen
© Chelsey Ritner, Exotic Bee ID, USDA.

Males of many bee species have another trait, one that could be essential for protecting the species against habitat disturbances: they are hopeless wanderers.

Most bees are solitary (each female builds her own nest) and philopatric, which is the tendency to stay in or return to the site of their origin. Females prefer to nest near the place of their birth because food or good nesting sites could be scarce elsewhere – why take chances with the unknown? This tendency to stay put may result in huge nest aggregations (e.g., the heather colletes, Colletes succinctus). But philopatry induces inbreeding, which doesn’t bode well for the future of a population. Males, however, who do not have a home or offspring to care for, can fly away in search of a mate outside the old, boring neighbourhood. Sexual attraction is governed by pheromones, and males of some species such as the vernal colletes (Colletes cunicularius) show a preference for scents produced by females from different populations (Vereecken et al., 2007).

A male vernal colletes, looking for love somewhere else © Aiwok, Wikimedia Commons.

The sugarbag bee (Tetragonula carbonaria), a stingless species endemic to Australia, demonstrates males’ dispersing capabilities. They roam an average of 2-3 km from their nests, more than twice the female range, to find a mate; some males cover 20 km, about 30 times the females’ range (Garcia Bulle Bueno et al., 2022). By dispersing over great distances, males are bound to transfer genetic material from one population to another, which is especially important if the species’ habitat has been fragmented by human activity. 

A sugarbag bee © Ken Walker, Museum Victoria, Wikimedia Commons.

The role of male dispersal in reducing the effects of inbreeding was inferred from the genetic structure of populations of the oddly named unequal cellophane bee (Colletes inaequalis) in an urban/suburban habitat in New York, USA (López-Uribe et al., 2015). This bee is solitary, but females nest close to each other in aggregations of up to 100 nests/m2. Sampled bees had greater genetic similarity within nest aggregations than bees chosen at random, an expected consequence of philopatry. But there were no signs of inbreeding among the 11 nest aggregations spread over approximately 40 km2, an indication of genetic exchanges between them. And there’s more: within nest aggregations, females were genetically more inter-related than males, a sign of sexually biased migration rates. These DNA analyses elegantly suggest that males are the main arbiters of genetic flow among unequal cellophane bee populations.

A: a female unequal cellophane bee at the entrance of her nest. B: A nest aggregation © López-Uribe et al., 2015

Sexual dimorphism has been largely attributed to intra-species competition, often in the form of males fighting each other for a female or to be chosen by one. But sexual dimorphism has a cooperative side: it allows males and females to specialise in what they do best, be it caring for the young, finding food, defending territory, and so on. In the case of bees, males do their bit by gallivanting around, and by doing so they help reduce the risks of inbreeding.

Sticky contrivances

 By Athayde Tonhasca

Somewhere in Britain during the Victorian years, a four-spotted moth (Tyta luctuosa) landed on a pyramidal orchid (Anacamptis pyramidalis), intending to sip some nectar. The moth certainly didn’t expect to end up with its proboscis – the elongated mouthparts of butterflies and moths used for sucking – covered with blobs of pollen. But that was the least of the moth’s problems, as disaster loomed: the hapless wanderer was captured by an unknown collector and became a model for George B. Sowerby (1812-1884), the illustrator of Charles Darwin’s masterpiece about orchid fertilisation.

An illustration from Charles Darwin’s book on fertilisation of orchids depicting the head of a four-spotted moth with its proboscis laden with several pairs of pollinia from pyramidal orchids. Names of the species involved have changed since then. 

Those globules of pollen attached to the moth’s proboscis are known as pollinia (sing. pollinium). Each unit contains from five thousand to four million pollen grains, depending on the species. The grains are stuck together with pollenkitt, an adhesive material found in almost all angiosperms pollinated by animals. A stalk-like structure connects the pollinia to a gluey pad known as viscidium, and the whole assemblage is often referred to as a pollinarium.

A pollinarium: the pollinia on the toothpick are held in place by the sticky viscidium © Frederick Depuydt, Wikimedia Commons.

Pollen grains lumped together in a sticky package are not easily carried away by water or wind. As Darwin learned from his observations and experiments, this is done by animal vectors, mostly wasps and bees (although moths, beetles, flies and birds do the job for reasonable number of orchid species). Having pollen grains in a single unit reduces wastage during dispersal, but it’s a risky strategy: a lost pollinium means no pollination at all. So orchid flowers have undergone dramatic morphological transformations to assure their pollinia are picked up by the right pollinator. ‘If the Orchideæ had elaborated as much pollen as is produced by other plants, relatively to the number of seeds which they yield, they would have had to produce a most extravagant amount, and this would have caused exhaustion. Such exhaustion is avoided by pollen not being produced in any great superfluity owing to the many special contrivances for its safe transportal from plant to plant, and for placing it securely on the stigma. Thus we can understand why the Orchideæ are more highly endowed in their mechanism for cross-fertilisation, than are most other plants.’ (Darwin, 1862, Fertilisation of Orchids).

What are some of these contrivances mentioned by Darwin? Orchids’ stamens (comprising anthers and filaments, the male reproductive parts) are fused with the pistil (which are the female reproductive parts: stigma, style and ovary) to form a structure known as a column. The anther (the pollen-producing organ) is located at the distal – away from the centre – end of the column, and the stigma (the pollen-receiving organ) lies close by. Directly below the column there’s an enlarged petal named labellum or lip, which often is noticeably different from other flower parts in its colour, markings, or shape. For nectar-producing species, nectaries are located at the base of the labellum.

Parts of an orchid flower © Thomas Cizauskas, CC BY-NC-ND 2.0.

So the stage has been meticulously set. The distinct labellum is a perfect landing strip for an insect attracted by the orchid’s rewards, be they real (nectar) or not (when physical or chemical decoys are deployed). The pollinator lands on the labellum, touches the tip of the column, and goes away with pollinia securely adhered to its body by the viscidium, which works better on smooth surfaces such as the eyes and mouthparts of insects and beaks of birds. When the pollinator visits another flower, the pollinia are likely to be transferred to the stigma. Sticky pollinia and viscidium ensure secure removal of pollen, minimal wastage during transit, and a high probability of deposition on a receptive stigma. 

An orchid bee (Euglossa sp.) with pollinia attached © Eframgoldberg, Wikimedia Commons.

These morphological features have evolved independently in two plant groups: orchids (family Orchidaceae) and milkweeds (subfamily Asclepiadaceae of the family Apocynaceae). But pollinia are relatively more important for orchids; with more than 26,000 described species, they make up about 8% of all vascular plants and span a range of habitats in all continents except Antarctica; there are more orchid species in the world than mammals, birds and reptiles combined.

Merodon equestris (a hover fly) tangled with milkweed pollinia © Lloyd Davidson, Creative Commons.

Orchids’ highly specialized ‘lock and key’ pollination system reduces the chances of pollen being picked up by the wrong flower visitor or being transferred to the wrong plant species; the selective adaptations towards the right flower-pollinator association must have contributed to orchids’ enormous richness and diversity of forms. It’s amazing what a dab of glue here and there can do.

Figure 2 from the 1877 edition of Charles Darwin’s Fertilisation of Orchids. Darwin is demonstrating an early-purple orchid (Orchis mascula) pollinium adhering to a pencil inserted into the flower. Within 30 seconds, the loss of moisture makes the pollinium bend forward to become perfectly positioned to touch a receptive stigma, were the pollinium to be attached to a bee visiting another flower.

Don’t come fly with me, let’s not fly, let’s not fly away

By Athayde Tonhasca

Insects made their first appearance on this planet between 450 and 500 million years ago. But they really took off evolutionarily – and literally – some 80 million years later when they acquired the ability to fly. From then on, insects could explore a three-dimensional world to occupy every nook and cranny of a habitat, escape predators, disperse widely and search for food more efficiently. Insects soon became the dominant creatures on Earth. 

Meganeura monyi fossil, one of the largest recorded flying insects (65-70 cm wingspan) from ~300 million years ago © Didier Descouens, Muséum de Toulouse. Wikipedia Creative Commons

The ability to fly gave insects so many advantages and opportunities that it may seem inconceivable to give it up. And yet, many species have done just that. Brachyptery (wing reduction) or aptery (loss of wings) is widespread among insects. It is easy to understand the uselessness or even disadvantage of wings for bedbugs, fleas, lice and other sedentary creatures. But winglessness seems odd for insects we commonly see flying about such as wasps, beetles, and butterflies.

For these insects, wing reduction or wing loss almost always happens to females: males usually retain fully functional wings. The large velvet ant (Mutilla europaea), is a case in point; the male is winged and a capable flier, while the female is apterous, a trait that makes her look like an ant – hence the species’ common name. But in fact this creature is a wasp that parasitizes several species of bumble bees.

A female velvet ant © Tiia Monto, Wikipedia Creative Commons

The reasons for the loss of flight in insects have baffled scientists for a long time, and Charles Darwin was one of the first to come up with a theory to explain it. Intrigued by the unusual number of apterous beetles on the island of Madeira, Darwin suggested that flightlessness was a survival strategy. To avoid being blown into the ocean by the strong winds that buffet the island year round, the local insect fauna adapted by losing their wings and keeping their feet firmly on the ground. 

Darwin’s theory was tested recently with data gathered from 28 Southern Ocean Islands, a collection of isolated, wind-swept specks of land in the southern regions of the Atlantic, Pacific and Indian oceans. About half of the islands’ indigenous species are unable to fly, which is nearly ten times the global incidence of flightlessness among insects.

Number of flightless (orange) and flying (blue) insect species in the Southern Ocean Islands © Leihy & Chown, 2020. Proceedings of the Royal Society B: 2872020212

By analyzing variables such as wind speed, temperature, air pressure, habitat fragmentation, and presence of predators or competitors, researchers validated Darwin’s hypothesis: wind speed was the main environmental contributor to flightlessness in insects. But Darwin didn’t get it quite right: the risk of being blown away is not the main evolutionary driver – after all, even a tiny island is a huge mass of land for an insect. Instead, the enormous energetic cost of flying seems to be the cause.

Indeed, brachypterous or apterous insects are more common in areas where a great amount of energy is required for flight such as arctic regions, mountains and deserts; or in stable habitats where dispersal is not vital for survival, such as caves, termite and ant nests, and on vertebrate hosts. Flight muscles comprise 10-20% of an insect’s body weight, and sustained flights consume a great deal of the insect’s resources. If flying does not give it significant advantages, energy could be spent on some other function – such as laying more eggs, for example.

Egg production explains why it’s mostly females that are wingless. Free of the costs of flying, a female can produce lots of eggs, which are considerably more expensive energetically than sperm. In fact, for many flightless species the female’s abdomen is greatly enlarged to hold as many eggs as possible, which increases the species’ chances of survival. Flight is retained in males probably because it increases their chances of finding females.

In Britain, the belted beauty (Lycia zonaria), the winter moth (Operphthera brumata) and the vapourer moth (Orgyia antiqua) are three of the better known species with wingless females. The belted beauty is a scarce species confined to coastal areas, but the other two are abundant and widespread; the winter moth is an invasive in North America. 

A male and a female belted beauty © Harald Süpfle, Wikipedia Creative Commons

Wings were the morphological feature that assured insects’ success on Earth, but many species made a U-turn in the evolutionary road. For them, flightlessness was the best life strategy. This apparent throwback is another demonstration that evolution is not teleological, that is, it has no objectives or ‘improvement goals’. It just provides the best means for a species to adapt and survive.

The drinks are on me

By Athayde Tonhasca

The broad-leaved helleborine (Epipactis helleborine) is found throughout UK and much of Europe and Asia in all sorts of habitats, including urban and disturbed areas. This orchid was introduced to America, where it is viewed as an invasive species in some places. Despite its common occurrence and being the source of a reasonable supply of nectar, the broad-leaved helleborine is often ignored by insects, a fact noted by Charles Darwin.

The orchid’s small, inconspicuous, greenish/purplish flowers are not exactly good marketing for attracting bees and other pollinators. But one group of insects are keen visitors: wasps, in particular the European (Vespula germanica) and the common wasp (V. vulgaris). 

A broad-leaved helleborine flower © Björn S., Wikipedia Creative Commons
A broad-leaved helleborine flower © Björn S., Wikipedia Creative Commons

Adult wasps feed mostly on carbohydrates, which they get from nectar – or from your sugary drink, if you give them a chance. But the nectar of broad-leaved helleborines is special: it’s laced with chemical compounds, some of them with narcotic properties. It also contains ethanol and other alcohols, possibly as the result of fermentation by yeasts and bacteria. This chemical cocktail is toxic or repellent to many visitors, but not to wasps: they lap it up. Unavoidably, a concoction of opioid and morphine derivatives plus alcohol, even in minute amounts, has consequences for its consumers. Wasps become intoxicated and sluggish after a few sips, which suits the orchid very well. They spend more time on the flower, staggering about and thus increasing their chances of ending up with a pollinium (a sticky mass of pollen grains) glued to their heads. Watch it. Nobody knows if wasps are hungover afterwards.

A wasp with pollinia attached to its face © Saarland, Wikipedia Creative Commons
A wasp with pollinia attached to its face © Saarland, Wikipedia Creative Commons

This orchid has another trick up its sleeve besides inebriating nectar; it also lures wasps with false promises of prey for their larvae. It turns out that these flowers release chemicals that mimic green-leaf volatiles, which are produced by plant tissues when they are damaged by herbivores. Wasps are attracted to green-leaf volatiles in the hope of finding some juicy caterpillars chomping on the host plant. When a wasp gets to the flower, its attention is diverted to the sugary nectar, so the scent scam is forgotten.

Orchids are highly diverse: with approximately 25,000 described species, they make up about 10% of all flowering plants. About one third of orchids do not offer food rewards – nectar or pollen – to visiting pollinators. Instead, they have evolved all sorts of tricks to attract insects. Some flowers have the shape, colours or scents of food-rewarding plants; they may bait male insects by resembling female counterparts, or by releasing pheromone mimics; sometimes they charm visitors that are seeking a place to lay their eggs. Or by using a combination of artifices, as it is the case of the broad-leaved helleborine.

These deceiving orchids attract only a handful of insects that respond to specific chemical or visual cues, so many potential pollinators are excluded. But the strategy pays. Pollen is transported more efficiently for deceptive species than for those with multiple pollinators. This means that more pollen is taken to another flower of the same species, and less is dropped or deposited on the wrong flower.

Deception works for orchids, but how about their cheated visitors? Sometimes they are rewarded, but often they get nothing. We don’t have much information about the insects’ side of this relationship. They must benefit somehow, or at the very least they are not significantly harmed. This matters to wasps, as they pollinate around 5 % of all known orchid species.

Orchids provoke much fascination for their biology, diversity and exoticism. This level of attention has helped us appreciate better the role of wasps. Most of them don’t collect pollen, and their lack of body hairs – compared to bees – does not allow for many pollen grains to attach to their bodies. But if we go by their contribution to orchids’ reproduction, these important but often maligned insects have much to reveal about their part in pollination services.

An European wasp, a frequently cheated pollinator © User:Fir0002, Wikipedia Creative Commons
An European wasp, a frequently cheated pollinator © User:Fir0002, Wikipedia Creative Commons