Ten years ago, being told that one could study ecology in the middle of the concrete jungle that Bangalore has become, would have drawn laughter from me. But a peek into the world of the fig, and its pollinator, the fig wasp, changed my mind completely. Fig trees such as the fluttery peepal or the stalwart banyan are very unlike the other roadside trees common in India; they never seem to flower, yet manage to fruit “magically” from time to time. The mystery of the missing flowers lies in the ‘secret gardens’ that figs make, and in the special relationship they have with fig wasps.
The partnership between the fig and fig wasp is an amazing one. Fig trees produce a ‘secret garden’ of tiny flowers in an enclosed, thick-walled edifice that looks like a fruit. The entry to this garden is a tiny hole through which only female fig wasps can pass. These female wasps pollinate the fig flowers and lay their eggs within this fortress garden. In return for the wasps’ pollination services, the fig tree provides nourishment and a safe haven for the wasps’ young. However, the partnership between figs and pollinator fig wasps, called mutualism, is not as ideal as it sounds. Within the microcosmic setting of the fig–fig wasp mutualism, a drama of exploitation, predation and parasitic life unfolds.
My story begins on a warm morning in September, when I set out to simply observe the partnership between a fig and its fig wasp. The roadside tree I was perched on was a Ficus racemosa, a cluster fig tree, also known as atthe-hannu mara in Kannada. Two weeks ago, small buds had formed on the long thin stems that festooned the trunk. The tree was starting to grow figs, its ‘secret gardens’, for a reproductive episode. This was a show not to be missed, so here I was, staring at the ever-growing round spheres. Over the last two weeks, the only visitors to the figs were a few fat, brown wasps. They would hover over the tiny figs, land, and remain motionless for hours together, apparently doing nothing. These were parasites called Galler Wasps.
Gallers are named so because these wasps inject a cocktail of venom along with their eggs, into the figs. The venom makes the fig grow a hard, rounded structure called a gall, which houses the wasps’ larva and provides it with food. Gallers offer no pollination services, but sit on the fig’s surface and deposit eggs into the fig using a thin, needle-like organ called an ovipositor. Galler larvae are parasites, consuming resources that were meant to raise seeds and pollinators. Although there had not been much to see in the last two weeks, it suddenly hit me – even before the two mutualist partners met, an exploiter had begun its insidious work.
Today, however, was a day of positive action. On approaching the tree, I had been aware of a faint, sweet fragrance emanating from the verdant green figs. The female flowers in these figs were ready to be pollinated, and were sending out a seductive fragrance to attract pollen-laden female pollinator wasps. And boy, were they successful! Millions of tiny, black pollinator wasps formed a living cloud around the tree. Soon, the openings of most figs were feathered with bunches of wings that the female pollinators left behind when they squeezed through the tight entryway. Female fig wasps die within the figs they enter, which has earned the fig the dubious honour of being named the ‘tomb flower’.
Curious about what was happening inside, I cut open one of these figs. The snowy white interior held three pollinators, busily moving around. The pollinators were spreading pollen and laying eggs into some of the fig flowers. The wasps’ antennae and wings were broken off, and their abdomens were pinched thin, a testament to their struggle through the tiny entrance. In a few short hours, these wasps would die, but they would have fulfilled their life’s goal of pollinating a fig and laying their eggs.
The orgy of pollination lasted for only two days. At the same time, along with the pollinator wasps flocking to the tree were more Galler Wasps. A different species to the Gallers I had seen before, these were brown, slim-bodied and had longer ovipositors. Exploitation seemed to be a constant background to the fig–fig wasp partnership.
A week or so after the eventful pollination, the figs had grown very hard, their walls thick with milky, foul-tasting latex. This week heralded another haze of wasps that enveloped the tree. These were parasitoids, a class of predatory wasps that laid their eggs on the developing pollinators and parasitic Gallers. The parasitoids’ larvae literally eat the Galler and pollinator larvae alive – a gruesome fact that highlights how even thick walls, sticky latex and hard galls cannot fully protect against a specialised predator.
One day, about three weeks after the parasitoid attacks, the figs began to look less green, more yellow, and had begun to soften. Suddenly, a black spot appeared on the wall of one of the figs I was watching. In a minute, the spot became a hole, and a troop of brown, wiggly bodies spilt out onto the fig surface. These were male pollinator wasps that had just cut a hole to freedom for their pollinator sisters and mates.
Essentially, in four weeks since the pollination, seeds and wasps (pollinators, parasitic Gallers and parasitoids) had grown side-by-side until fully developed. Male wasps hatch first and mate with females. The interior of a fig at this stage hosts uninhibited sexual revelry, with males of several different wasp species scrambling and fighting to mate with females. What is truly amazing is that despite the crowd and the lack of visual clues, males still manage to find females of the right species to mate with.
Pollinator males then cut a hole through the fig wall, while pollinator females stuff their chests with pollen. Once the hole is made, the male pollinators die, while the pollinator females take to the skies in search of another fig tree with a ‘secret garden’ ready to be pollinated. The pollinator females are fragile, living for no more than a day or two. But they are amazons of the skies, riding wind currents and flying large distances – up to 160 Kms – to find figs they can pollinate. The female Gallers and parasitoids also fly out at the same time to find figs to plunder and raise their brood. The wasps emerging from figs attract a bevy of predators – spiders, ants and dragonflies flock to the fig tree to feast on dying male and emerging female wasps.
The figs, now empty of wasps, had ripened to warm oranges and deep reds, heralding a different type of banquet. They were also scenting the air with a fruity odour that attracted hosts of squirrels, barbets, mynahs, parakeets and even a troop of bonnet macaques. In the evening, fruit bats began to visit. The bats continued to swoop down on the figs until late into the night, showering me a few times with their fluid, seed-filled ejecta. Later still, perhaps a few minutes after midnight, I heard an unearthly scream – another nocturnal visitor. The beam of a flashlight lit up a tiny face with two large, amber eyes, high up in the fig tree’s branches – a Slender Loris. It was difficult to believe that all this animal life I was seeing was actually next to a busy darshini on a roadside in Bangalore.
For five years of my life, a part of each day was spent under Ficus racemosa trees. Those years earned me a doctoral degree in ecology, but more than that, they taught me to appreciate why figs are called keystone resources. They are the stalwarts that can anchor and support a delicate web of life, even in the unloving concrete jungle of a busy urban city.