An Ant-Plant Love Story on the African Plains

56 SWARA OCTOBER - DECEMBER 2011 www.eawildlife.org

SPOTLIGHT

An ant-plantlove story on the africanplains

SWARA OCTOBER - DECEMBER 2011 57 www.eawildlife.org

SPOTLIGHT

By Dino J. Martins

On the high, windswept plains of East Africa lies a mystical world based on

a tempestuous, eternal love affair between insects and plants.

Imagine a world woven of a tapestry so detailed that it is almost mind-boggling to consider. Confronted with the scenario of myriad ants living on plants that stretch from horizon to horizon, the mind struggles to make sense of what’s going on. But in Mother Nature’s apparent chaos, there is a refined order.

At first this thorny, tangled world seems dauntingly and impossibly complex, perhaps even incomprehensible. The best way to understand this complicated world is to look closely. Like many dynasties, this one is founded by royalty. A single future ant queen makes her way into the world. This tiny, obscure act hints at the grand scheme that sustains the savannah.

It rained softly during the night. The air smells hopeful, spiced by the downpour. And all around me on trees still studded with raindrops, there is frenetic ant activity. I peer closer at one tree.

A young queen is silently chewing her way into the young, green Brussels sprout-like ‘gall’ of a Whistling Thorn (Acacia drepanolobium). There has been a mating flight of ants and all around young queens are returning to the acacias, frantically seeking new homes. This moment is the birth of a partnership between plant and ant. Both partners contribute to its success and, sometimes, to its failures.

Basically the Whistling Thorn provides two essential needs: food and housing. Food takes the form of nutritious nectar secreted from special glands on the leaves, called extra-floral nectaries. Housing comes from the swollen thorns, which are often called galls. Of

course, there’s no such thing as a free lunch, especially in nature, and the ants repay their gracious host by providing a standing army. They provide security against the hordes of hungry mouths that would dare feast on the acacia.

I return to watching the drama of the young queens. Among the thorns, a wisp of webbing trapped one stray queen. A small yellow spider, just two thirds her size, shoots out from under a sliver of peeling bark above. The young queen struggles in vain. Within minutes she is a neatly wrapped silvery bundle of protein.

The scurrying workers, initially so keen and defensive of the young queens, rush by, ignoring her plight. This incident introduces the less savoury aspects of colony life: all individuals are completely dispensable, only the colony matters. The whole, the common good always comes before the self.

In fact, some scientists have argued that social insects function as part of a communal psyche, a ‘superorganism’, controlled alternately by instinct and chemicals such as trail pheromones. All the decisions, responses and choices made by individual worker ants are thought to be only an extension of the colony’s needs and responses to stimuli.

Over 10 years of watching these ants, I have learned that the pulsing of this system is like a slow, steady heart beat through ecological time. And the blood that drives this rhythm is rain.

Africa is vast. In fact, there’s a saying that the world is smaller than Africa. It is also a thirsty continent. And here in East Africa, the plains’ thirst is quenched just twice a year. The rains come with monsoon winds from the Indian Ocean. And much of life, both plant and animal, is driven by this cycle.


Against incredible odds only a tiny handful of young queens make it from their mother colonies to establish their own. Most are despatched by birds, spiders and other predators as they departed the trees of their birth.

Even fewer managed to soar high enough to join the mating swarms in the sky above. Once mated, the young queens return to the trees. They must find one that is both available and young enough so that they can chew their way into a domatia, all the while dodging predators, and other hostile ants and with the clock ticking away. So many cards need to be played right in this precarious gamble so that the young queen will be able to start a new colony on a Whistling Thorn.

Sometimes two or more young queens arrive at a young Whistling Thorn simultaneously. However, they do not confront each other directly. The battle is fought once the queen has a retinue of workers to fight on her behalf against other young queens and colonies.

As I daydream about these questions, the queen has chewed her way into the young domatia of the Whistling Thorn. She wriggles into it, disappearing from view. That’s it. She will never again emerge into the outside world.

Now, hidden from view, safely cloistered in her new home, she will set about the task of laying eggs and tending larvae which will become the nucleus of a young colony. She will nourish them from her own reserves of

SPOTLIGHT

TOP: The caterpillar of the carnivorous Ciliate Blue butterfly living inside a swollen thorn with the ants. MIDDLe LefT: Adult female Ciliate Blue butterfly laying an egg. MIDDLe RIGHT: Crematogaster nigriceps ants tending their host acacia. BOTTOM: Giraffes and elephants around the Whistling Thorn trees in Laikipia.


SPOTLIGHT

fat. Once the first workers emerge, they will forage over the acacia and bring back energy distilled by the Whistling Thorn in the form of liquid food from the nectaries. But for now she is on her own. She will remain an egg-laying machine for the rest of her life.

A pilgrimage of giraffe moves through the trees. They pause to watch me. The giraffe have something interesting to teach us about this partnership. Some ants can behave properly towards their Whistling Thorn host, while others cheat on the partnership – defaulting on paying for their room and board by not providing security.

The Whistling Thorn tree needs its ants. The plants receive protection from the ants against herbivores, and selection has favoured those plants that attract and maintain the most effective ant guard. This is especially relevant for plants in Africa because the African plains are home to large herds of hungry herbivores. They are also home to countless legions of smaller, but no less effective, insect herbivores in the form of armies of locusts and caterpillars. It is this pressure exerted by hungry

herbivores of all sizes that drives much of the partnership between the ants and the plants.

I look up at the giraffes around me. This is a fully habituated herd. So long as I am quiet they will ignore me completely. Only through watching very closely can I see if these lofty beasts have anything to say about the tiny ants on the acacias.

I watch the giraffes feed. One bends over just 10 feet away and solemnly extends its long blue-black tongue, wraps it around a mass of leaf and thorn, and pulling back, reaps a mouthful of chlorophyll-fixed energy. It straightens its attenuated neck and chews ponderously. I can even see the lump of leaves, thorns and ants make its way down the first part of its spindly throat.

All around the same motion is being repeated over and over. The giraffes amble about, seemingly nonchalant. But as I have been watching them very closely, I am not fooled by the peaceful charade. The pattern that emerges is stunning and clear. Not all ants are equal. Different ant species differ markedly in their tending abilities on

the Whistling Thorn. The aggressive Cocktail Ants are effective at limiting browsing by both giraffe and other large browsers. And most effective of all is the Red-Headed Cocktail Ant. Giraffes spend barely a couple of minutes feeding on these trees before moving on. The ants silently swarm out and file into the nostrils of the big mammals. Cocktails Ants bite and then, in the equivalent of extreme ant yoga, reach their abdomen over their heads and wipe the acid-laden sting into the bite.

In contrast, the shy Skinny Black Ant has little effect on the large browsers. Giraffe and other browsers feed freely from these trees for long periods of time while the terrified ants cower inside their thorny homes.

Now the sun is directly above in the sky. The ants are marching around their acacias. The system is buzzing with life. I glimpse a fragment of iridescent energy that zips by me furiously. It is a tiny, robust butterfly. And it too has something interesting to say about the ants.

I tap my net against a low branch, and once again startle a small butterfly, which settles back on a spray of leaflets

ABOve: A Carpenter ant (Camponotus braunsi), a less common inhabitant of the Whistling Thorn acacia. TOP RIGHT: Skinny Black ant (Tetraponera penzigi) ants - this is one of the more widely distributed ants on the Whistling Thorn. BOTTOM RIGHT: the Red-Headed Cocktail (Crematogaster mimosae) one of the most aggressive defenders of this acacia.


with green, sickle-shaped seed pods. It shuffles its hind wings gently, showing off its tails. These are not just beautiful, they are meant to trick predators into grabbing the wrong end, thereby allowing the butterfly to escape. Lies and deceit are everywhere in nature.

I catch a glimpse of the exquisite blue-purple iridescent colours on its wings. This is a Hodson’s Ciliate Blue, a member of the Lycaenid butterfly family that includes the Blues, Coppers, Hairstreaks and Metalmarks. These tiny, exquisite, gorgeous and devious butterflies are found the world over and often closely associated with ants.

This particular butterfly cannot survive without the ants on the Whistling Thorns. It uses the relative safety of the swollen thorns as a

place for caterpillar development and pupation. It lays its eggs on leaves of the tree and the caterpillars live and feed in the swollen thorns with the ants, who don’t just tolerate them but tend them constantly and lovingly.

If you are lucky enough to find the well-camouflaged caterpillar, a closer look will reveal a strange ritual. Several worker ants will periodically stroke the caterpillar, producing a drop of liquid from a gland on its back. Believe it or not, the ants are “milking” the caterpillar. As part of their relationship with the ants, the caterpillars secrete a sugary solution called honeydew as a reward for the ants.

This relationship is so finely tuned that should the caterpillar not be milked, it will die from infection

SPOTLIGHT

The ants of the Whistling Thorn. TOP LefT: Red-Headed Cocktail Ant (Crematogaster mimosae). MIDDLe LefT: Black-Headed Cocktail Ant (Crematogaster nigriceps). BOTTOM LefT: Skinny Black Ant (Tetraponera

penzigi). Illustrations on the right show the alates (young virgin queens and males) of the three ant species.


from moulds. The ants, on the other hand, gain vital amino acids from the caterpillars, that develop these through feeding on the nitrogen-rich foliage of the Whistling Thorns.

The relationship between the two species seems to favour the butterflies. But alas, the butterflies do something really sneaky to the ants. Using stable isotopes to track the diet of the various partners, it has emerged that the caterpillars feed not just on the foliage but also on the ants’ larvae! Yes, they are carnivorous!

The butterflies are also faced with a choice of ant-hosts on the acacias. Do the butterflies have anything to say about the ants? Which of the ants is the favourite of the Hodson’s Ciliate Blue? Searching for Hodson’s Ciliate Blue caterpillars and adults always led me back to the same ant. Yes, you guessed it, the ‘good’ ant: Red-Headed Cocktail.

So being a good ant in this partnership not only means chasing off hungry herbivores, but it also makes you more attractive to parasites. As we all know, successful partnerships soon attract hangers-on!

I return to watching the butterflies. One female flutters about nervously. She weaves up and down, gently touching the foliage, then fussily rises back into the air. She repeats this movement over and over. Then she circles a twig lined with fresh buds and leaves. She alights and, grasping the young leaves, curves her abdomen forward.

Muscles and antennae twitching, she gently deposits a pearly-green egg onto the leaves. After that effort, she strokes her antennae briefly, flicks them over the egg once - the only interaction she will ever have with her future offspring - and departs.

Within seconds, patrolling ants have located the egg. They find it irresistible. Ants gather around it like the faithful at an icon. They lovingly stroke it with their antennae standing in a perfect circle around it. This egg, and the caterpillar that will soon hatch from it, will have a constant ant guard until the day it seals itself into a cocoon and begins the miracle of transformation that will see another butterfly emerge to start the whole complicated process all over again.

Now, in the warmest part of the day the acacias are buzzing with life. Intrigue and evolution dance all around.Flirtatious butterflies swirl about in arcs and wheels. Furtive parasitic wasps with long dagger-like ovipositors (egg-laying devices) hunt among the thorns for unsuspecting young queens to stab with gruesome eggs that will hatch and feed inside the bodies of their doomed hosts.

Comic jumping spiders shuffle about, dodging ants, then grabbing one for a quick snack when the others aren’t looking. In the distance another herd of giraffe waltz by, serenaded by a pair of courting Crowned Cranes, whose melancholy, regal cries fill the air.

A lone bull elephant, stupendous and magnificent, walks in a straight line, pausing to sniff at the Whistling Thorns with its trunk. It brusquely pushes trees over and then delicately strips the bark away to chew like liquorice. In terms of numbers and distribution, ants saturate the environments they live in. You simply can’t ignore them. As the biologist E. O. Wilson so eloquently put it, “Through most of your life, you are never more than a few feet from an ant.”

So it is not just mind-boggling but also inspiring to think of all the

Whistling Thorns stretched from horizon to horizon on plains across Africa. And of all the ants that live in them, faithfully working hard or lazily hiding. And of all the other creatures, known and undiscovered, great and small, and all still so little understood, whose lives the ants touch in a myriad ways. So the world is indeed smaller than Africa.

Tiny ants make a huge difference to the planet. We would do well to pay them more attention. Next time you walk by these fellow inhabitants of the world, whether on the sidewalk or the savannah, please spare them a thought and a glimpse.

Now I must return to the ants.

DInO J. MARTInS is a Kenyan naturalist, artist and writer studying how insects influence both human life and the way the world works. He studies the intricate connections between insects and sustainable human enterprise. He asks that everyone spends a few minutes a day looking at an insect as a means of enlightenment and inspiration. Questions/comments about insects: [email protected]

SPOTLIGHT

Dino J. Martins and some guides admire a Whistling Thorn acacia in the Western Serengeti. These incredible trees are found all across East Africa and well-worth spending a few minutes looking at the ants and other creatures.

An Ant-Plant Love Story on the African Plains

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