Readers’ wildlife photos

Athayde Tonhasca Júnior sent another text-and-photo lesson, which is indented below. Click on the photos to enlarge them.

Tiny killers’ gigantic army

The bark louse Echmepteryx hageni (order Psocodea), an obscure fungus-eater from North America, is no more than 10 mm in length. Unsurprisingly, its eggs are miniscule. But these small dollops of nutrients are plenty for the egg parasite Dicopomorpha echmepterygis, a wasp in the family Mymaridae, which are known as fairyflies or fairy wasps. We have little information about this parasitic wasp, but we do know that males are blind, wingless and phoretic, that is, they need to cling to another organism to move about; in this case, females are their ride. Males also have no mouthparts, so they cannot feed.

A bark louse E. hageni; its eggs are parasitized by D. echmepterygis © Katja Schulz, Wikimedia Commons:

If you suspect that a male D. echmepterygis shouldn’t expect a long and prosperous life, you are right. He lives off the nutrients taken as a larva from one of his host’s eggs, and those reserves won’t last long. But that’s of no consequence for the male; his only purpose during his short existence is to impregnate a female, which, conveniently, is his means of transportation. He only needs to crawl to the appropriate spot on her body to do the deed. This lifestyle is by no means unusual; many other parasitic wasps have similar traits. But D. echmepterygis males have a unique claim to fame: they are the smallest adult insects on Earth, measuring 139 µm in length (Mockford, 1997). [JAC: that’s a little more than a tenth of a millimeter!]

Male D. echmepterygis ventral view (scale line = 50 μm) and head (scale line = 20 μm) © Huber et al., Wikimedia Commons:

To have wings and be able to fly, other fairyflies have to be bigger, but not by much: the winged and marvellously named Tinkerbella nana is 250 µm long. We can have a better appreciation of these fragile fairy creatures by considering the hardships of being small:  the risk of desiccation and barriers unknown to larger animals such as surface tension and fluid viscosity. Michael LaBarbera’s The Biology of B-Movie Monsters is a highly entertaining and illuminating discussion on the physical limitations of body sizes. For a deeper exploration, D’Arcy Thompson’s underappreciated classic On Growth and Form is a tour de force of the physical properties acting on biology.

L: The fairyfly Tinkerbella nana (scale line = 100 μm) © Huber & Noyes, 2013. (CONTENT WARNING to University of Aberdeen’ students: the following refers to J.M. Barrie’s emotionally challenging Peter Pan). The genus Tinkerbella was named after Tinker Bell, while the nana epithet was inspired by the Darlings’ dog Nana – which is also a derivation from nanos, the Greek word for dwarf. R: A micrometre scale for comparing the sizes of D. echmepterygis and T. nana © Zeiss Microscopy, Wikimedia Commons:

There are many fairyflies besides D. echmepterygis and T. nana: over 1,400 of them. And these are the known species; certainly the true number is much higher. All described species are egg parasitoids (their young develop on or inside another organism, eventually killing it) of a range of insects, and they are good at finding their victims: some fairyflies parasitize eggs embedded in plant tissue, buried in the soil and even submerged in water.

Fairyflies belong to one of the many families of Chalcid wasps or chalcidoids (superfamily Chalcidoidea). This is an enormous group of about 22,500 known species, although the total could reach over 500,000 (Noyes, 2019). Most of them are small (less than 3 mm) parasitoids of different life stages of many insects and arachnids (spiders, mites, scorpions and others).

L: A female Richteria ara justifies the fairyfly epithet. Scale line = 1000 μm (1 mm) © Huber, J.T. R: A much larger chalcidoid: Conura sp. © Judy Gallagher, Wikimedia Commons:

A great number of insects and other arthropods have to live with the high probability of bumping into a chalcidoid wasp, but that’s not the half of their problems. Around 25,000 species of Darwin wasps, or ichneumonids (family Ichneumonidae), and some 17,000 species of braconids (family Braconidae) join forces in a vast army of parasitic wasps – and again, these figures are likely to  grossly underestimate the real number of species.

As the story goes, J.B.S. Haldane (1892-1964), British/Indian geneticist, evolutionary biologist, mathematician and more, found himself in the company of a group of theologians. On being asked what one could learn about The Creator from studying his creation, the atheist Haldane is said to have answered ‘an inordinate fondness for beetles.’ Haldane may have said something of the sort, and indeed a Celestial Big Cheese would be seen as partial to the order Coleoptera. With nearly 400,000 known species, beetles lead the biodiversity table, comprising about 25% of all animal species (excluding Bacteria and bacteria-like Archaea). But there is strong bias here: beetles are popular and relatively easy to find, while most parasitic wasps are very small, hard to identify, and tricky to handle and preserve in collections. It’s a lot of work, and there are not many specialists in the area. But the more they look for parasitic wasps, the more beetles’ predominance is challenged. Most holometabolous insects (those with four life stages: egg, larva, pupa, and adult) are attacked by one or more hymenopteran parasitoid, sometimes five or even ten, although we may not know their identities. By modelling parasitoid-to-host ratios for some groups of insects, Forbes et al. (2018) estimated that hymenopterans easily beat beetles in the biodiversity league. Some coleopterists may not like to hear that.

Number of named species as of 2022 © Hannah Ritchie, Our World in Data. “To a rough approximation and setting aside vertebrate chauvinism, it can be said that essentially all organisms are insects” (May, 1988). Parasitic wasps may be greatly responsible for that:

Parasitic wasps are practically everywhere. In just one suburban garden in Leicester, England, Owen et al. (1991) collected 455 species of Darwin wasps, some new to the British list, in a two-year period. These wasps have an enormous sway in the structure and composition of biological communities. They limit the numbers of insects and spiders, and, by keeping herbivores in check, they have an indirect but vital influence on the diversity and abundance of plants.

Trioxys complanatusovipositing into the body of a spotted alfalfa aphid (Therioaphis maculata) © CSIRO, Wikimedia Commons. ‘Insects. . . in all likelihood exert a greater impact on terrestrial ecosystems than any other type of animal. They are the glue holding an ecosystem together: in their millions they consume plants, and in their millions they are consumed by other organisms’ (LaSalle & Gauld, 1991). And in their millions they are killed by parasitoids:

We can gauge the regulatory power of parasitic wasps by their efficacy as commercial biological control agents. For example, Encarsia formosa is one of the most efficient weapons against whiteflies in greenhouses, while Anagyrus lopezi saved cassava crops from the ravages of mealybugs in Africa and Asia.

L: Cards containing E. formosa eggs to be placed in glasshouses © Dekayem. R: A. lopezi, a scourge of mealybugs © CIAT, Wikimedia Commons:

LaSalle & Gauld (1993) estimated that at least 50% of the 150,000 or so species of Hymenoptera are parasitoids. They all have the alarming habit of eating their hosts from inside their innards while they’re still alive, which seems execrable and cruel. Darwin was dismayed by it, as he expressed in a letter to his friend Asa Gray in 1860:

‘I am bewildered.— I had no intention to write atheistically. But I own that I cannot see, as plainly as others do, & as I sh^d wish to do, evidence of design & beneficence on all sides of us. There seems to me too much misery in the world. I cannot persuade myself that a beneficent & omnipotent God would have designedly created the Ichneumonidæ with the express intention of their feeding within the living bodies of caterpillars, or that a cat should play with mice.’

Despite Darwin’s misgivings, parasitic wasps are not particularly shocking, considering that approximately 40% of all known species are parasitic (Dobson et al., 2008). And these tiny, fragile agents of doom are just a fraction of many others such as viruses, fungi, protozoa and worms, who have an array of imaginative ways to cause sickness, suffering and ghastly deaths. Haldane’s god, so fond of beetles, also has a kinky sense of humour.

Relative abundance of different taxa, and the proportion of parasitic species in those taxa. The area of a circle corresponds to the natural log of the total number of species in a taxon © Dobson et al., 2008:

But such anthropomorphic considerations are misguided. Parasitoids, parasites and predators are regulators of the natural world. They prevent excessive population growth, including of agricultural pests and disease vectors, and remove the old and sick from the general population. Parasitism helps shape biodiversity and ecosystems, so it is not intrinsically bad or good. It is a characteristic of life on our planet. It is as it is.

‘Morality is a subject for philosophers, theologians, students of the humanities, indeed for all thinking people. The answers will not be read passively from nature; they do not, and cannot, arise from the data of science. The factual state of the world does not teach us how we, with our powers for good and evil, should alter or preserve it in the most ethical manner’ (Gould, 1982).

‘We entomologists, who have no charismatic elephants to hide behind, no cuddly panda bears to hug before the public, no aesthetic whooping cranes, no passion-inducing spotted owls, no thousand-year old forest giants – we entomologists are at the forefront of the biodiversity battle with only our bugs for a shield’ (Grissell, 1999):