Ants, Ants, and Ants, or, The Ultimate of the Ultimates

Harvester Ants, Monomorium sp., rush in and out of their underground nest carrying grass seeds and husks.

If there’s a bustle in your hedgerow, don’t be alarmed now

It’s just a spring clean for the May Queen

Part I: Ants

It is no exaggeration when one says that ants are the ultimate animals shaping the world. But no one says it openly or publicly. The very few who write are read by the fewer few who really read only about ants and all things ants do. And ants do everything a man or an elephant does. So, between making a statement calling ants ultimate and having no one to attest to, I’m left only with my fascination for ants to try to back up the bold claim. Anyone who likes any particular organism calls it the ultimate – of course the redwoods are ultimate, the tiger is ultimate, the elephant – ultimate, the woodpecker, the king cobra, so on. Ants are not merely ultimate in that sense. They’re not big or colourful or, in vertebratalist sense, individualistic and intelligent. But they are all of these things as one superorganism – this obviously well-known term is rarely acknowledged as something unique evolution has done on our planet. It warrants some discussion.

Of all life to exist in the Kingdom Animalia, social animals are not the norm. Among terrestrial animals, it is a few that display this trait – roughly only 2% of animal species are social – from ants to elephants (but mostly bats when it comes to mammals). Sociality spans a broad spectrum of interspecies interactions, from presociality as defined by most solitary species, to prosociality, as defined by human societies based on a give-and-take interaction. The epitome of this is eusociality, where individuals don’t merely function as members of a colony but as organs of an individual – the superorganisms. Very few of the social animals are eusocial, and only two types of animals have mastered it – ants and termites. There are 15,700+ species of ants and under 3,000 species of termites.

Marauder Ants (ants are generally greatly better than humans), Carebara affinis, moving through ant-made tunnel carrying their young ones with them in an evergreen forest undergrowth.

Well, being eusocial doesn’t earn one the title of being ultimate. What we aren’t reading into is that there are nearly fifteen thousand, and an estimated twenty thousand, species of ants being superorganisms on this planet. To put it in a perspective, there are about 11,071 species of birds and about 6,399 species of mammals – both combined barely make up the entire family made up of ants, Formicidae.

Well, one would say they’re small, and usually small animals have various avenues for speciation and expansion, unlike large-bodied birds and larger mammals. But look at it this way: if larger means less diverse, why does larger mean that they have greater influence on their habitat? This is where the conundrum lies, one that ecologists – mostly entomologists – have been trying to answer. If it is quantitative, there is one way to look at this: a superorganism.

Weaver Ant, Oecophylla smaragdina, building a bridge connecting two distant branches together.
Every ant counts.

Unlike an organism that is a sum of its parts, a superorganism is more than the sum of its parts. Between taking birth as a single egg, mating, and dying, a superorganism can do more than just heal. An injured ant dies, but really, the superorganism may be hundreds of years old, even thousands, living attached and detached, with multiple colonies acting as independent brain nodes borne of the same progeny. Clearly, there is no other organism than termites and fungi who can do this, maybe humans but not really.

Just as it takes a herd of elephants to move a forest, it takes a colony of ants to influence their habitats – from the nomadic hunting colonies who are ever on the move to the sedentary foragers and harvesters, ants often make up the bulk of macro invertebrate fauna in a given place. A conservativeestimate by scientists puts the number around 20 quadrillion, or 12 megatons of Carbon – more than the combined biomass of all wild birds and mammals, and about 20% of human biomass. To put it in a perspective, there are about 450 thousand elephants, over 200 million even-toed wild ungulates and nearly 16 million wild carnivores in the world (see this, and this).

Harvester Ant, Messor himalayanus, carrying Bidens pilosa seed to its nest in the Shivalik hills of the lower Himalaya - ants are dedicated seed hoarders and would harvest edible seeds of invasive species such as B. pilosa in absence of native ones.

And if the numbers don’t mean a thing, there is one collective action that ants do as a clade that all herbivores and carnivores don’t do combined: occupy niches not reachable to the large animals – the microhabitats, and as a community of species affect habitats at landscape levels – the macrohabitats. This aspect of ants is less understood, but we’re getting there. Ants occupy multi-layered and overlapping niches, from the tallest canopy of the rainforest to deep underground where many species who only occasionally surface, dwell. Ants forage and farm, scavenge and hunt, and shape habitats as seed harvesters and seed dispersers to changing the whole vegetation in some places.

The thing is, I can go on and on about ants, and since my bias lies towards both, ants and elephants, I still think that today, ants are shaping the world in ways that eclipses elephants of today. There are two aspects to this theory: one, that ants are among the most devastative of invasive species on the planet and two, that elephant or in general wild herbivore and carnivore numbers have significantly fallen over the century. But the conundrum remains: to quantify the influence of Formicidae over all wild mammals combined is difficult.

Black Crazy Ant, Paratrechina longicornis, in an uncoordinated but effective frenzy carrying carcases of an Ichneumon wasp and a dragonfly back to their nest.

It is also a question of why, why do I say this? Aren’t all species responsible for influencing their habitats and thereby ecosystems? An ant cannot build dams like beavers, an ant cannot disperse seeds hundreds of kilometres like elephants, and so on. All are valid. What I’ve been at odds to tell you is that it is not species-versus-species, it is about something we perceiving as small having a profound impact on an ecosystem which we think only large bodied organisms do. I’m trying to tell you that ants are as much ecosystem engineers as the elephants, but maybe more. What makes them ultimate is not merely their sheer abundance – they are seemingly omnipresent among insects – but the way they function is beyond the scope of our very understanding of how ecosystems interact with animals – our way of thinking is very mammal – and to an extent but not quite, bird – centric. Generally speaking, insects don’t quite fit into our understanding of ecosystem functioning, for we focus only on the give-and-take system they interact with, like pollination and degradation.

There are two ways to understand the ultimatism of ants in the ecosystem – to study ant communities across ecosystems, and to study the ways in which ants interact with other ultimates of the ecosystems.

Part II: Ants

Insect communities are fascinating to observe. The macro-world and the micro-world are bound by the same biophysical mechanisms. The interaction where a tiger ambushes a herd of deer or a pack of wolves stalks a herd of antelopes, is being played out in every square meter of the forest. And there is more. It is a three-dimensional chess, there are insects flying about to hunt or to locate nectar, there are caterpillars dangling from a thread, spiders with two and three-dimensional webs, and there are the above-ground and below-ground insects – some live on the forest floor, some burrow in the soil.

Needle Ant, Brachyponera sp., show a unique altruistic trait where a worker carries another worker, called 'tandem carrying' to the source of food, to save its energy.

I have had the fortune of staring into a square meter of forests from various parts of India. The mixed deciduous forests of Central India, the rainforests of Western Ghats, and the riverine woodlands of Brahmaputra. And just as every square inch of a habitat is different, every such microhabitat hosts a different composition of insects, unique in the different microhabitats within a region as well. Our understanding of invertebrate communities is rudimentary and geographically scattered, but it suffices to say here that they are unique, more unique than vertebrate communities, even if influenced by the same factors such as physical barriers like mountains and rivers, climate and temperature, and the vegetation compositions. Ants display this variation surprisingly well and are probably the ideal indicators of the change at microhabitat levels.

My rudimentary, short-term observations in Kanha (Central India), Kadmane (Central Western Ghats), and Kaziranga (Brahmaputra floodplains), have documented 35 genera of ants. About 60% of these were unique to each site, 20% common to all the three sites, and 20% common in two of the three sites. This is possibly reflected among butterfly, bird and mammal communities as well, but when it comes to ants, our expectation of such a variation is undermined by their sheer numbers. A crude comparison I did back in 2016 was the correlation between ant numbers (opportunistic carnivores) and spider numbers (obligate carnivores) in a square meter area: I found both to be negatively correlated – more ants meant less spiders, but more spiders didn’t necessarily mean less ants. In areas dominated by ants, there was hardly any diversity of other insects. They not only influenced abundances but also diversities of invertebrates. Yet, surprisingly, they also existed in densities of as many as five ant species within a square meter area, each occupying niches within microhabitats.

Composition of ants (Genus) of the three sites I've spent some time looking for. A: The overall unique and common genera and B the region-specific unique genera.

For the three sites at Kanha, Kadmane, and Kaziranga, the unique genera were 43%, 33%, and 35%, respectively – not a large variation, but a curious one, nonetheless. Curious because of their habits – most ants are opportunists (hunting, scavenging, and mutually tending to other insects) besides being strictly herbivores (most of them are seed harvesters). When it comes to mammals, the carnivore and herbivore communities don’t change much unless the habitat drastically changes – from grasslands to woodlands. A megaherbivore will use multiple ecosystems and thereby exercise a greater influence in terms of space. For ants, while space is comparatively a limiting factor for a species or a community (though this is not the norm), their habits in their respective microhabitats, driven not only by their diversity and abundances, has an effect on the microhabitats that may be greater than that of megaherbivores on multiple ecosystems and space. Collectively, ants may do a lot more to locally influence a habitat by predating on other animals and seeds, than elephants do.

Is there a proof for this? Yes and no. What we do have are hypotheses. I reiterate here that despite comparisons – which are warranted because we live in a heavily mammal-biased world – the objective is not who wins the title, but to initiate a conversation about ants and by extension insects and their influence on shaping our world. Why the hypotheses have weight has a history dating back millions of years.

Black Crazy Ant, P. longicornis, carrying a possibly injured follow worker, being stalked by a kleptoparasitic fly - stealing food from ants is one of the common strategies amongst flies.

In 2021, an iconic publication stated at the outset: “In between Earth’s poles, ants exert impacts on other biota that are unmatched by most animal clades.” The publication is a rare gem into the world – our world – being shaped by ants. (In fact, read it now before proceeding with my rant.) It leads one down the rabbit hole of what has fascinated me for years now: the myrmecophiles and the myrmecophages – the ant-lovers and the ant-eaters, respectively.

Spiny Ant, Polyrhachis lacteipennis, tending to mealybugs on a grass blade. The ant-bug relationship is a classic example of mutualism which is often symbiotic in nature.

Many plants rely on ants for dispersal. Many plants produce an oily protein-rich blob attached to the seed called elaiosomes, to be picked up especially by ants that carry them into nests to eat, but some also germinate. This is called myrmecochory. Many invertebrate groups love to exploit the exceedingly productive ant societies. Some stick insects mimic these seeds, which are picked up by ants, and receive protection from predators and are dispersed around the area (for more, read this fascinating publication). Some of the earliest known invertebrates that preceded insects, the silverfish, evolved to live with ants as myrmecophiles feeding off what the ants brought to their colonies, many of the blues butterflies evolved to live within ant colonies by secreting a chemical that mimics the chemical language of ants. Then there are crickets who similarly live within ant colonies and interact with them as if they are a member of the society. And finally, the beetles – especially the Rove Beetles – who not only integrate themselves into ant societies but also look and smell like specific ant species they infiltrate. All these relationships have been shaped by millions of years of evolution – evolution wrapped around ants. If you thought ants exploited ecosystems because of gaps in the niches that could be filled up by superorganisms, here is a case of niches being created by these superorganisms for thousands of species to depend on them.

Ant-associations in Kaziranga's riverine woodland forests: one will see very many positive sum and negative sum associations in a square inch forest area, all leading to ants.

And this is not even half the story. A whole gamut of ant-eaters has evolved, right from tiny beetles and bugs and spiders to vertebrates – the pangolins and anteaters and bears. There is a group of birds called Antbirds (families Formicariidae and Thamnophilidae), many of the species follow army ants to find insects flushed by this gigantic army-on-the-move. ‘Anting’ is a common habit of birds where they rub off ants onto their wings for a ‘dusting’ using their crushed bodies – using formic acids, an ant’s ultimate weapon – to remove parasites. Spiders have taken the very shape of ants to blend among them and hunt them. Perhaps the anteaters manifest the ultimate influence of ants – not merely as ecosystem engineers, but biological engineers, by their mere existence. While not the most speciose, the mammalian family Myrmecophagidae is well-known for its giant anteaters, so specific to the diet of social insects that their whole body is shaped around what they eat. The pangolins and the sloth bears are some of the well-known ant and termite eaters.

As mammals, we call these traits adaptations – that these vertebrates have ‘specialized adaptations’ to feed on ants. Rarely do we see it from the other lens, that the ants have modified mammals the way grasses have. On that note, there may be a strong association between the long-term survival of grasslands and ant communities, but it has not been explored yet.

Part III: Ants

Ant-animal and ant-plant associations are legendary. On one hand, ants tend to other animals in return for food – the mealybugs, aphids, hoppers, and other Hemipteran bugs excrete excess sugars which ants love to sip. Many blues butterfly caterpillars have specialized glands that secret these sweet extracts, called honeydew, which ants feed on and in turn protect them from parasitic wasps and other predators. On the other hand, plants, too, specialize by building cavities to house ants and produce nectar to attract them in return for protection. These relationships mammals (and birds) share with the ecosystem pale in front of the multiple, multidimensional, and multitaxa symbiotic ties with ants – and this is not just to say that ants are the ultimate of the ultimates, but that through their diversity and sheer numbers, and despite being extraordinarily small, they influence ecosystems to the scales we don’t give them enough credit for.

Yellow Crazy Ant, Anoplolepis gracilipes, is one of the most invasive of species on the planet. While native, it forms large colonies in India and may be outcompeting many rare ant species under our noses.

These influences, at times, are devastating. One of the most destructive of invasive faunal species are ants – not only do they outcompete other ants, they drive ecosystem collapse. The Christmas Island story, where the Yellow Crazy Ant (of which I wrote in 2013) drove the whole island into a disarray and many endemic species towards extinction, is infamous. The Argentine and Tropical Fire Ants have reigned supreme outside of their native range, making them one of the clinically important species for humans – receiving far more attention than even venomous snakes. But this is where the narratives about ants limit: that they are invasive. Of the top 100 invasive species (flora and fauna), only 14 species are insects, of which only 4 species are ants – of the 15,700+ species.

Arboreal Bicolor Ant, Tetraponera rufonigra, scavenging on a - comparatively - elephant-sized head of a dead male Giraffe Stag Beetle, Prosopocoilus girafa, in Western Ghats.

This eclipse cast upon ants isn’t helping them or us. Ants are industrious, daring, and unstoppable, but they are also not humans to be identified as ‘invaders’ – all the invasions have happened because of human machinations transporting people and food. Fortunately, many good things about ants are said and written and filmed – there is no dearth of it. The dearth, the crux of this long rant, is in realising that ants are the ultimates shaping ecosystems far beyond any mammal. In this day, ants surpass all faunal species in designing the world we live in, perhaps not as much as bacteria and virus and livestock, but among all large wild animals.

One of the ways in which ants interact with elephants goes beyond the ant-versus-elephant trope. While I could rant on, I would end for now with a fascinating study that blew my mind: ants affecting lions. Yes. Across East Africa’s savannah, the whistling-thorn tree (Vachellia drepanolobium) shapes the ecosystem. It is a myrmecophyte, living symbiotically with the acacia ants (Crematogaster sp.). Whenever herbivores try to feed on the leaves, the ants attack, limiting the destruction caused by herbivores. They are especially effective against elephants who topple trees to feed on the leaves. Elephants eat a lot. The authors note that in the last two decades, the big-headed ant (Pheidole megacephala), native to Asia, invaded the African savannah and outcompeted the native acacia ants, driving them out of the trees or entirely laying ruin to their colonies. The mutualism afforded by the whistling thorn tree and the acacia ants thus ended, and was not replaced with the big-headed ant, who did not evolve to return the favour. As a result, the authors note, elephants broke trees five-to-seven times more than in uninvaded areas, gradually changing the vegetation of the area. Through three-years of observations, the authors found that invaded areas afford greater visibility, negatively affecting the chances of lions hunting zebra who are able to escape quickly. In the authors’ words: “… interactions between lions and their primary prey, the plains zebra, are mediated by a foundational ant-plant mutualism. Lions and other large carnivores use tree cover to conceal themselves, such that their success in hunting plains zebra was higher where visibility was lower. By disruption the foundational mutualism between whistling-thorn trees and native acacia ants, invasion by big-headed ants renders trees more vulnerable to browsing by elephants, thereby reducing tree cover and increasing visibility.” This, they state, has likely led to lions switching to other prey species, preventing negative effects on their population size.

Asian Marauder Ant, Carebara diversa, are a common forest floor dwelling ants seen moving in large columns made up of small workers and gigantic soldiers. 

This is one of the startling and bold studies looking at the cascading effect of ants, from niche-specific interactions to ecosystem-wide impacts. It is remarkable because cascading effects are usually top-down, driven by apex species – mostly predators – down to the producers, the plants. Here, the dynamics are shifted – indicating the impact of species upward and downward of the cascade.

Weaver Ant, O. smaragdina, overpower a Queenless Ant, Diacamma rugosum, solitary forager when it stumbles into their stronghold. Queenless Ants forage solitarily and Weaver Ants as groups. While the Queenless Ant worker is capable of delivering a painful sting and the Weaver Ants cannot, here the game is of sheer numbers.

As in physics, ecology warrants extraordinary evidence for extraordinary claims. This observation is indeed extraordinary backed by data, yet it must be tested by multiple independent sources. The viral and awe-inspiring videos of how the return of the wolves – the apex predators – to the Yellowstone National Park in the US led to a sort of an ecosystem revival is an important cautionary tale. The premise was that once the wolves returned, the elk population was brought under control, enabling riparian vegetation to grow, which in turned encouraged beavers – the keystone species of the riparian ecosystems – themselves ecosystem engineers, to return and do what beavers do – build dams. This was a typical ‘trophic cascade’ in works, lauded by everyone. Subsequent studies, especially this study that aimed to quantify the strength of this trophic cascade, showed a 1500% increase in willow crown volume, suggesting instead that this situation is of ‘ecological hysteresis’ – the condition of more than one stable state. Another study showed an absence of reversal, attributed to other factors influencing the ecosystem, forming an ‘alternative stable state’. The authors’ noted: “The promotion of ecosystem restoration by apex predators suggests there is a “quick fix” for losing them from food webs. We have shown that the ecosystem state that emerged following the loss of large carnivores from the food web resisted reversal after they were restored.”

Weaver Ant, O. smaragdina, carries a bark scorpion to its nest. It seems like the ant triumphs over one of the most venomous arthropods of the forest undergrowth.

In view of calling ants the ultimate of the ultimates, it is important to look at all possible mechanisms at play when ecosystems change – ants might be one cog in the wheel of the savannah of East Africa, if not the gear that shifts it. The evidence of ants capable of doing it is so far more robust than wolves being able to do it. In discussing ants and elephants and wolves, I present an argument that ants are the ultimate ecosystem engineers that have not only influenced but changed ecosystems at a scale no wild mammals have or can. This doesn’t mean that conservation should not be prioritized. Elephants, wolves, and most large mammals are threatened by humans, from being killed in retaliation to poaching, and their habitats are being destroyed at an alarming pace. Threats to ants so far are practically unknown. A way forward is to observe both as a part of the ecosystem, ant and elephant, such that no organism big or small weighs the other down.