Tigers Of The Undergrowth
The role of tiny arch-predators, such as spiders, in the ecological cycle is similar to that of the tiger, suggests Aniruddha Dhamorikar, who studied spider diversity and density in the Kanha Tiger Reserve.
Photo: Aniruddha Dhamorikar.
A damp, glossy litter of leaves cloaks the dark forest undergrowth. The sal trees, with their lush green leaves, have shadowed this undergrowth for years, and bear silent witness to the stories that unfold beneath them. Walking on sal litter is slippery business, but walking underneath the canopy of these trees is ethereal, and the sights and sounds are reminiscent of an ancient forestland riddled with hushed winds and the echoes of birds. As we walk through this cold, damp forest, we see clues of something that happened last night: a trail of blood shining on the dark forest floor. The forest guard proposes a hunt, and he postulates the predator to be a tiger, leopard, or dhole – any one of Kanha’s famous carnivores.
THE FIRST HUNT
The forest is aglow with the early light of the day, and echoes the call of a Crested Serpent-eagle gliding over the mountains. Everything seems to be in place – chital grazing along the forest-edge, birds singing on branches, and a peaceful silence seems to have engulfed the woods. In the undergrowth, however, a fight for survival ensues, hidden from plain sight. A teneral robberfly that metamorphosed earlier that night prepares to unfurl its waxy, translucent wings. It staggers upon little mud-boulders as its cuticle slowly hardens and darkens, and the haemolymph is pumped into its body and wings as it grows in size and strength. Close by, a jumping spider belonging to the genus Phlegra lies in wait, watching patiently as the pale robberfly scampers over the forest floor. It carefully orients itself as it follows the robberfly, a thin silken thread marking its way of approach. Its eyes never leave its potential prey, and it carefully manoeuvres itself on top of a little pebble.
The spider, almost half the size of its prey, pounces on the callow robberfly from behind, burying its fangs deep into the soft thorax. The robberfly is not ready to give up as yet. It rebels, tries to fly away, and protests until the effects of the venom rapidly take over. It ultimately succumbs to the attack, and with a raised forelimb, announces its surrender. The spider then retreats under a small plant as the venom slowly dissolves the robberfly from the inside. All of this takes place in under five minutes.
There is no ruckus of langurs, no cacophony of birds, and no trace of the hunt that just took place. The sal trees stand silent, the first rays of the sun now making their way through a crack in the canopy. Standing here, and looking all around, I can see at least seven large orb-webs of the giant wood spider spanning from tree to tree, their anchor-threads that work like beams of a building stretching as long as four metres in length. On shrubs closer to the ground, the web of an orchard spider catches the early sunlight, splitting it in the hues of a rainbow as it dances in the morning breeze. A two-tailed spider, the tree-bark hunter, waits patiently for a passing ant, its excellent camouflage hiding it from prying eyes. In this land of the tiger, another supreme predator has claimed its own niche, and is very much the tiger of the undergrowth – the spider.
Photo: Aniruddha Dhamorikar.
TRANSECT THREATS AND EIGHT LEGS
I was studying the diversity and density of the spiders of Kanha, a project undertaken by The Corbett Foundation in association with the Kanha Tiger Reserve, and was looking to find any clues to their preference of habitats in the vastness of this tiger reserve. What I found made me realise that there’s another predator that has been right under our nose, sharing intricate behaviour of hunting, courting, and looking after its young ones, just the way the top predator of Kanha does.
The forest guards who so kindly accompanied me on transects were at first dumbstruck at the task at hand – counting the spiders of Kanha; but all of them, trained in quadrant method to determine groundcover, were a great help – or, were considerate enough to call out to me if they spotted something under the litter which they could not identify. We usually set out during the early morning hours. Armed with axes, bamboo sticks, cameras and hand lenses, we trod the forests and meadows intently searching for arachnids. The walks were usually dominated by talks of tigers and bears, especially while we counted spiders near their pugmarks and scats.
The talk that especially unnerved me once was of a mother tigress threatening a forest guard and watcher on their daily patrol of the forests we were surveying. She had taken shelter amongst some rocks behind dense Lantana shrubs during the monsoon from where the transect line passes. Luckily, they escaped unscathed, and remained bold enough to re-tread that forest patch. No tigress threatened us on that hot day, but her pugmarks and those of her cubs stood distinctly along the riverbank, reminding us that this was her home and that we were uninvited visitors. Every blind turn made me anxious about what lay in wait, every sudden movement in the thickets was startling, and I started counting spiders hunched over the forest floor with someone to look over my shoulder.
So this is what it feels like, I thought, to be the one hunted. But my mind always turned to spiders, and their prey, insects. The forest floor and the grasslands were teeming with scores of crickets, woodroaches, grasshoppers, moths and beetles, and counting them was critical to counting spiders, since the prey ultimately determined the density and diversity of predators.
What I found is quite perceptible in a relationship between predator and prey. It was evident that prey species are just as vital for the survival of the spider as they are for the tiger. In comparing different ecosystems like sal forests, mixed deciduous forests, bamboo groves and grasslands, ecosystems with higher tree-cover and dense leaf litter showed higher diversity and density of spiders since these ecosystems offer richer sources of food and hiding places for insects – the primary prey for spiders – making it a crucial niche in the vastness of an ecosystem. On the other hand, some places – especially those affected by human activities and cattle grazing – showed the lowest numbers of insects since the productivity and plant diversity in these regions were low, which in turn affected the spider population.
The density and diversity of spiders was the highest in sal forests, famed as the hunting abode of the tiger. What I had set out to explore became quite evident: that sal forests, for their near-evergreen nature, their moist, dense undergrowth, offer an excellent niche for insects and other invertebrates to live in, which predators such as spiders have learnt to exploit.
Photo: Aniruddha Dhamorikar.
MAINTAINING THE WEB
How else, other than their obvious size, is a spider different from the tiger? With 22 families of spiders recorded in Kanha so far, they have successfully carved a niche for themselves, some so vivid in their hunting tactics that they will astound you: from some jumping spiders like Portia that stalk and prey on other spiders, and giant wood spiders like Nephila that spin large intricate orb-webs over 10 m. above the ground, to spitting spiders like Scytodes that spit venom and silk to ensnare their prey, and those that are probably the only ones like humans to create a web like a fishing net to capture prey, the net-casting spider, Deinopis. All these members of Araneae show that the success of spiders lies in the ways they have evolved and mastered over eons to capture prey.
With rapidly developing techniques in the fields of taxonomy, we have a fair idea of who the spider is, and how it captures its prey, but we’re still riddled by what role they play in an ecosystem, and ultimately, why we need to study them. My quest for documenting the spiders of Kanha was not only to figure out how many there are, but to try to bring them to the forefront for doing their bit in maintaining the balance in an ecosystem, just the way tigers do.
The answer to why we need to study them is therefore as simple as the answer to why we need to study tigers: spiders are obligate carnivores, relying strictly on a prey-base of insects and other invertebrates. In a way, spiders control their populations just as tigers control herbivore populations. Biologists and naturalists have emphasised the fact that spiders can be used as an indicator of the health of an ecosystem, just as the presence of tigers determines the health of a landscape.
Determining their density and diversity helps us in filling the blanks in our understanding of the health and basic functioning of an ecosystem. For instance, a large diversity and density of spiders implies an abundance of insects which are herbivores, carnivores, detritivores, or scavengers in nature. These provide priceless ecological services of pollination, population control, and decomposition and biodegradation of organic matter. The higher density of insects and spiders also indirectly implies the availability of protein-rich sources of food for vertebrates.
In direct benefit to humans, the ecological services of spiders have a potential that is far more critical today – in food production. A significant portion of our food crops are damaged by insect and mite pests, with scientists estimating over 15 per cent of the 40 per cent damage is done by insects and mites alone. Most of these pests are controlled by chemical pesticides to which several pests have developed resistance. Alternative biological pest-controlling agents, such as parasitic wasps and flies, and predatory beetles and bugs, are some pioneering models used in biological pest control, however their prey species range is narrow, leaving a gap in the efficient control of pests. But spiders may challenge the proliferation of pest species. Since spiders prey on a wide array of insects, they are being explored as the ultimate choice of controlling insect pests in fields as well as in food storage. Their worth in monetary terms, therefore, could be quite significant in protecting our major sources of food.
Photo: Aniruddha Dhamorikar.
When I look into the eyes of a spider, those simple ocelli staring straight at me, I do not see it as an organism for man’s benefit; I see an organism that has no ulterior motives, and an individual with a purpose – with determination – that is akin to that apex striped predator we all praise and admire. And after roaming the woodlands of Kanha observing spiders, I noticed something more in common between the two predators that share nothing in common in their genetic or phenotypic makeup: that just as spiders flourish under the protective shadow of the tiger, tigers owe plenty to them as well.
Yet I feel that spiders, those eight-legged invertebrates we all love and hate for our own reasons, are more than just an allegory of the tiger. We don’t know how many spiders call our forests home, or how many are the last ones we share our planet with. A world without tigers will make a lot of difference to us, but what about a world without a single species of spider? Jeff Corwin, in his book 100 Beats: The Race to Save Earth’s Most Endangered Species, reflects upon a phenomenon he calls the ‘charismatic species syndrome’, where attention is given to a particular species more so than others of equally crucial ecological importance. He says, “the reality is, each species, no matter how big or small, has an important relationship with other species in its ecosystem – and we’re in a race to preserve as much of the animal kingdom as possible.”
Just as you take pleasure in watching the elegant gait of a tiger, it is worth giving a glance to a jumping spider stalking its prey, or sitting by a net-casting spider spinning its net, and watching tiny Theridula spiders building long elaborate gum foot web mazes to entrap prey. We often tend to feel disgusted by the cobwebs in the corners of our homes, and hence we tend to completely disregard these underdogs of the ecosystem, but that maze of cobwebs is a trap for pests such as mosquitoes. In houses I have visited in villages, I have frequently observed in the cobwebs of the daddy longlegs spider in the genus Crossopriza several dead mosquitoes – both Aedes and Anopheles. So far there are no concrete estimates of how many mosquitoes a spider kills; but here they are silently helping the people get rid of harmful diseases such as malaria which is rife in villages along the southern periphery of Kanha.
Spiders, amongst every other creature alive today, do not merely exist, but are a part of the play of the universe. Studying these little marvels is just a small step towards understanding nature and unravelling its many mysteries hidden deep in places like this undergrowth, where they reign supreme.
Author: Aniruddha Dhamorikar, First appeared in: Sanctuary Asia, Vol. XXXV No. 8, August 2015.