Readers’ wildlife photos (and story)

Today we have another photo-and-text lesson from Athayde Tonhasca Júnior. Athayde’s text is indented, and you can enlarge the photos by clicking on them.

Enormous armies with countless skills

As natural history narratives go, the 1954 ant-inspired motion picture Them! was not up to David Attenborough’s standards because giant, deranged, radioactive ants don’t exist. Despite the factual liberties, the film was a commercial success and had the novelty of depicting two myrmecologists (ant specialists) as heroes who helped to save the planet from a myrmecological doomsday. Malevolent ants have a long history in Western popular culture. In The Empire of the Ants (1905), H.G. Wells tells us the story of a gunboat forced to turn around and abandon an Amazonian village overwhelmed by intelligent killer ants.

A bad ant infestation in the New Mexico desert © San Bernardino Sun, 1954. Wikimedia Commons:

Those who have witnessed an army ant raid or had the unfortunate experience of stepping (or even worse, sitting) on a fire ant mound, understand why ants elicit fear or a grudging respect; many of the 14,147 – and counting – species of ants (family Formicidae) are territorial and highly aggressive to perceived intruders, man or beast.

Lieutenant da Cunha being overwhelmed and killed by evil Amazonian ants in H. G. Wells’ The Empire of the Ants © Amazing Stories, 1926.Wikimedia Commons:

JAC: I’ve added the video of the army ant raid (narrated by David Attenborough) below; do watch it

But aggression is only one aspect of ants. They can be predators or feed on seeds, nectar, honeydew, or fungi they cultivate. They are found everywhere except Antarctica and a few remote islands, and are incredibly important in decomposing organic matter, recycling nutrients, and controlling plant-eating insects (many of them agricultural pests). Ants are essential ecosystem engineers: many species build nests and dig tunnels in the ground, increasing aeration and drainage, and improving soil fertility with their waste and food stores. Some seed-eaters are important for plant reproduction: they stock their nests with seeds that are not all eaten. The spared lucky ones germinate in a nutrient-rich, herbivore-free environment. More than 3,000 plant species depend on myrmecochory, which is seed dispersal by ants. Plant-eating by ants is not always benign; leafcutter ants (genera Atta and Acromyrmex) are incredibly destructive; in Brazil, saúvas (their local name) have been the scourge of agriculture since the beginning of European colonisation. French naturalist Augustin Saint-Hilaire (1779-1853) supposedly said that ‘Brazil must destroy the saúva or the saúva will destroy Brazil’, which was a slogan adopted in successive – and unsuccessful – eradication campaigns.

Digging a leafcutter ant nest in Brazil. Concrete was poured into the nest to create a cast of the inside. The nest covers more than 67 m² and contains 1,920 chambers © O’Brien & Bentley, 2015:

All these ecological services and impacts are intensified by ants’ mindboggling numbers. The distinguished myrmecologist E. O. Wilson estimated that 10¹⁵ to 10¹⁶ ants crawl on Earth’s surface at any given time (that’s quadrillions, figures usually discussed in astronomy). A later appraisal fine-tuned the number to 20 × 10¹⁵ individuals, which corresponds to ∼12 megatons of carbon. This is more than the combined biomass of all wild birds and mammals, and is equivalent to ∼20% of human biomass (Schultheiss et al., 2022). Another study following a different methodology suggested a population size of 5 × 10¹⁶, excluding arboreal ants (Rosenberg et al., 2023). So Wilson wasn’t far off, as a billion here or a billion there is not that important when we are talking quadrillions. For comparison, there are some 7.9 × 10⁹ human beings on the planet.

A representation of powers of 10 to help us grasp the magnitude of ants’ abundance: each block is ten times the size of the previous block, up to a billion (10⁹). One quadrillion would be 1.000.000 bigger than the billion block © Cmglee, Wikimedia Commons:

Ants are everywhere and interact with a vast number of animal and plant species, but they seem to be mostly absent from one ecological process: pollination. Which is a bit puzzling, considering that bees, their close relatives, are the main pollinators of a large number of plants. Many reasons have been proposed for the dearth of ant pollination, from their grooming (self-cleaning) behaviour to scant ‘hairiness’ (body bristles), resulting in few pollen grains being transported. But bees groom themselves, and some ants are as hairy as bees. The ‘antibiotic hypothesis’ is the most accepted explanation for ants’ unsuitability for pollination. Most ant species feature a specialised gland located in the metapleuron (a thoracic plate; pl. metapleura). The metapleural gland – and to a lesser extent some other parts of the body – secrete chemicals that serve as signals for nest-mate recognition and territory marking, and especially as antiseptics that prevent the proliferation of bacteria and fungi. But these substances have a disagreeable side effect: they also inhibit pollen germination and the growth of pollen tubes.

Parts of a typical ant, highlighting the all-important metapleural gland © Mariana Ruiz, Wikimedia Commons.

Ants’ chemical defences seem to make them incompatible with the job of pollination. Which is a pity for the plants’ point of view, as ants often crawl all over them in search of nectar from their flowers and, in some cases, from specialised nectar-secreting glands. But inevitably and predictably, natural selection intervenes to fill the voids of missed opportunities.

Honewort (Trinia glauca) is an unassuming herb found on dry, rocky sites with sparse vegetation in southern England. Elsewhere, it ranges from continental Europe to southwest Asia. On some of the English sites, flowers of this rare plant are visited mostly by ants, especially Lasius alienus, which are also their main pollinators (Carvalheiro et al., 2008).

Honewort on limestone, a habitat shared with its main pollinator, L. alienus © BerndH, Wikimedia Commons.

Honewort is an addition to the ever increasing number of reported cases of myrmecophily, or pollination by ants. These ant-friendly plants may have developed tolerance to the ill effects of metapleural gland compounds. This seems to be the case for the waxy-leaved smokebush (Conospermum undulatum) in Australia: in an experimental setting, pollen from some plant species suffered substantial decreases in germination after contacting the integument (‘skin’) of Camponotus molossus and other ants. Pollen of waxy-leaved smokebush however was not affected. Not surprisingly, ants contributed significantly to the plant’s pollination (Delnevo et al., 2020).

A, B: waxy-leaved smokebush flowers. Bee visitors: Leioproctus conospermi (C) and Apis mellifera (H), which only steals nectar. Ant visitors: C. molossus (D), C. terebrans (E), Iridomyrmex purpureus (F) and Myrmecia infima (G) © Delnevo et al., 2020.

Brute force is another possible explanation for myrmecophily. A single ant may be a poor pollinator, but a mass of them visiting flowers repeatedly may end up doing the job properly. Apparently this is the scenario in high mountains and arid zones, where ants make up a substantial proportion of flower visitors (Gómez et al., 1996).

In their monumental 1991 Pulitzer Prize-winning book The Ants, Bert Hölldobler and Edward Wilson skimmed over myrmecophily, as it was viewed as a minor feature. Bees, flies and moths are by far the champion pollinators, but more and more studies suggest ants are important for some plants in some habitats. So we can add pollination to ants’ long list of ecological services – unhinged, angry and radioactive ants notwithstanding.

Edward Osborne Wilson (1929-2021), myrmecologist, environmentalist, secular-humanist, and pioneer in the fields of ecology, evolution and sociobiology. Despite underhanded attacks from some of his peers while he was alive and attempts at character assassination by the Woke Rabble after his death, Wilson remains one of the greatest and most inspiring scientists of our times © Jim Harrison, Wikimedia Commons.