Life Without Light: Creatures of Meghalaya’s Caves

Entering a cave in Meghalaya is like opening a mystery box — you never know what you will encounter. Shining a torch into the smallest of these caves throws up secret passages, lucent pools of water, underground rivers, and deep caverns. Hidden in this otherworldly realm are the most unexpected, extraordinary and enigmatic life forms. In this lightless, subterranean space, a variety of creatures live and thrive in pitch-black darkness. In early 2021, wildlife photographer Dhritiman Mukherjee, a crew of filmmakers, and I set out to explore these fascinating cave systems in Meghalaya’s East Jaintia and East Khasi Hills.

Finding, entering, and investigating these caves for natural life is no easy feat, but these fragile habitats and the life they sustain make the arduous journey to the caves and exploration of these underground spaces worthwhile. These life forms make up a unique and limited biodiversity. Some of the super-specialised and niche species have evolved in such specific ways in these environments that the collapse of one cave system could wipe out numerous life forms in one fell swoop.

The history of the formation of Meghalaya’s caves is as fascinating as the story of how life appeared in these cavernous depths. Equally intriguing is how all the species in a cave system depend on each other for survival, each playing a distinct role in this delicate subterranean ecology. In our explorations of these caves , we had the opportunity to understand how this interdependence played out. Over two weeks, we explored the river cave Krem Chympe, the vertical shaft cave Krem Umladaw, and several other lesser-known caves.

Different Forms of Cave Life

The fauna in these caves can be classified into three categories: troglophiles, trogloxenes, and troglobites, names derived from the Greek word “trogle”, for hole, cave, or cave-dwelling. Spiders, crickets, and other insects, as well as some bats, fishes, and frogs that are typically found in the wet caves, are known as troglophiles — cave residents that can also live comfortably on the surface of the earth.

Trogloxenes or cave guests are those that make the cave their part-time home. These would typically include creatures like some bats and birds like swiftlets that use the caves to roost.

Then there are troglobites, whose name itself has a zing to it. These are the cave superstars, creatures who have adapted to the caves in a manner that enables them to spend their entire life cycle in this environment. Characterised by evolutionary adaptations like an absence of pigmentation, loss of eyesight, and development of sensors suited to a world without light, troglobites are the rarest and most enigmatic life forms in these subterranean habitats. Meghalaya has over 1,600 caves, more than any other state in India. However, even in these caves, troglobitic species are uncommon, and their existence tenuous.

In the relentless humidity, intense darkness and unvarying temperatures, food is a scarce commodity. Plants cannot grow here in the absence of sunlight. Organic matter is either carried into these caves by streams of water, or falls into small crevices and makes its way down. Oxygen levels are low, and cave critters have very low metabolism. These factors limit the occurrence of true cave-adapted species to small aquatic or semi-aquatic organisms and insects. The world’s largest troglobitic fish, which we were fortunate to see in Krem Umladaw, is an extraordinary exception to this in terms of its sheer size.

The narratives of how cave creatures came to exist in these dark depths are as fascinating as personally meeting these unique creatures in their domain. Professor Khlur Mukhim, a bio-speleologist who has studied life in Meghalaya’s caves, explains that it is usually the monsoon rains and overflows that bring life forms into these cave habitats, from where they cannot get out. In exceptional cases, where the population survives, speciation, the process by which populations evolve to become distinct species, occurs — the washed-in creatures slowly adapt over generations to survive in cave conditions.

Owing to their isolation, this evolution can be so specialised that sometimes caves in the same region are home to different species derived from the same basic family of fish or insects. This means they are usually critically endangered and in danger of becoming extinct, their survival often strictly bound to a specific underground habitat. “Sometimes you can find different levels of adaptation in the same pool in a cave,” Mukhim remarks. “I have also found troglobitic species in a small stagnant pool in Krem Khung.” Interestingly, Mukhim shares that in a recent cave expedition, he found a fish species which has large eyes, but no obvious recognition of motion.

The Circle of Life

The interdependence between the various creatures occupying these caves plays out in a fascinating web. In addition to the food brought in by occasional floods, cave dwellers also depend on cave guests who forage outside the caves for insects and fruits and return to the cave to roost. On our first day exploring the stunning river cave Krem Chympe at dusk, we witnessed the spectacular flight of a large colony of bats leaving the cave to feed. Two days later, we were about a kilometre in when we saw what must have been over a hundred thousand of these furry flying mammals lining the roof and the walls of the cave, as far as the eye could see and our torches could illuminate. We were looking at a large colony of leaf-nosed bats, possibly intermediate or Schneider’s leaf-nosed bats. These bats serve a vital function — their guano provides nutrition for others inside the cave. By foraging outside and coming back to roost in the caves, they provide food for those who can never leave. “Bat guano or faeces is a very important food source,” explains Mukhim. Centipedes, cockroaches, springtails, mites, millipedes, fish, and cave crickets all thrive on bat guano.

Perhaps the large colony of bats in Krem Chympe supports the diversity of aquatic life I saw while diving in the water — glass shrimps, crabs, large tadpoles, and loaches (bottom-dwelling freshwater fish).

Not surprisingly, Meghalaya harbours half of the recorded bat species in the country. These include the Pearson’s horseshoe bat (Rhinolophus pearsoni), great roundleaf bat (Hipposideros armiger), and the rare Wroughton’s free-tailed bat (Otomops wroughtoni) that until recently was thought to be confined to the Western Ghats. Meghalaya’s only fishing bat, Rickett’s big-footed-bat (Myotis pilosus), has also been seen during caving expeditions. This is a fascinating species with special claws for hunting fish.

Bats also support creatures in other ways. Elaborating on these cave relationships, Mukhim observes, “Some flies are very well adapted to living in the fur of bats.”

Caves are also used in several ways by resourceful surface dwellers. Snakes come in through crevices to catch easy prey, sneaking in and out with ease. We also spotted telltale signs of porcupines, mice, and other surface dwellers in some of the shallower dry caves. I learnt that mice feed on cave crickets and that some birds hunt and nest close to cave entrances.

We also found the most unexpected life in unnamed caves. At the entrance of one such cave, the team surprised a crab-eating mongoose hunting near shallow water. A stone’s throw away, we squeezed through a slender crack to enter a stunning horizontal limestone cave with sheets of rock embedded with fossils. The ceiling and walls glinted like diamonds in the dark, and a closer look revealed the eyeshine of gigantic huntsman spiders, each the size of my hand or even larger. Further in, pools of stagnant water with eels, loaches, and shrimps greeted us. As we continued inwards, the water became much deeper with underwater crevasses. Above the lucent pools, we spotted cascade frogs (genus Amolops) on a sharp overhang.

In another unnamed cave that we reached after a half-hour trek just past a cement factory, we spotted whip scorpions, cave crickets with extra-long antennae, huntsman spiders, and bacteria and fungi which glowed gold and green in the torchlight.

There is still much to learn about these fascinating and enigmatic creatures of the deep. As more caves are explored, more species will be discovered — already new species of bats, a troglobitic crab, and small populations of two critically endangered species of blind fish (Schistura papulifera and Schistura larketensis) have been identified. They are indeed cave superstars whose stories of evolution and survival over millennia challenge our imagination. Their survival depends on conserving their limited, niche habitats that lie underneath the surface of the earth in Meghalaya.