Indian bull frog: the Andamans’ new colonisers

The Indian bull frog, a recent arrival from the mainland, is steadily occupying the islands’ ecosystem and threatening the local economy. Mohit M. Rao reports on the bizarre man-frog conflict brewing in the islands

A narrow road bifurcates the hyper-green paddy fields of Webi village in Middle Andaman, in the Andaman and Nicobar Islands. A clear stream flows around the Webi, home to the Karen community, brought to these shores from Myanmar 93 years ago.

At dusk, as fading sunlight paints the surrounding hills in silhouette, the calls of cicadas, crickets and frogs rise in crescendo. In the cacophonic stillness, a centipede winds its way across the empty weathered road. And then, in the blink of an eye, it’s gone, swallowed whole by a recent migrant to the island — the Indian bullfrog (Hoplobatrachus tigerinus).

Indian bull frog: the Andamans’ new colonisers


Barely 10 cm long, this particular specimen is small. But the larger ones weigh at least half a kilo. The golden stripe on their backs and the glitter around their throats shine in the diffused light of a mobile phone. Less than 2 ft from the centipede-eater sits another frog. Next to that, one more, and another, and another… scores of frogs in varied sizes, basking in the warmth of the asphalt. Every now and then, one of them leaps toward the murky waters of the paddy fields. There is nothing frog-like about the deep, guttural croaks of these prolific breeders. Rather, they sound more like a bull with a sore throat.

“It wasn’t here even five years ago. Now they’ve taken over the village,” says Nau Thaw Raytoo, a mother of four, who lives in a concrete-bamboo house with her children, their wives, and her six grandchildren. Her broken Hindi shifts to fluent, high-pitched Karen when instructing raucous kids.

Webi is just among the scores of villages in the islands where the amphibian has arrived in hordes. An unusual man-frog conflict is brewing. The voracious animal gulps down anything that would fit in its jaws: centipedes, leeches, native frogs, lizards, small snakes, and even chicks and ducklings, which are an important source of food for the islanders.

“I’ve seen them eat chicks, swallowing the head whole,” says Raytoo, adding that of the 15 chicks hatched in the family’s chicken coop this year, only three have survived. Balakishore, whose father is Ranchi (an overarching term for Jharkhand tribals who were settled here to clear the forests decades ago) and mother is Karen, has lost 50 ducklings to the frogs. When grown, each duck would have fetched at least ₹300 in the local market.

One invader, many names

In the villages carved out of the virgin Andaman forests, the amphibian invader has evoked both surprise (“where did they come from?”) — and anxiety (“when will they go away?”). The bullfrog, found widely in mainland India and protected under Schedule IV of the Indian Wildlife Act 1972, is making the most of a free run that it’s enjoying in the erstwhile penal colony.

In the Andaman Islands, it can rain eight months of the year. The first rains in May are the signal for the bullfrogs to come out of the streams and agricultural ponds that have become their shelters. They breed by the hundreds, with each female able to lay between 3,500 and 20,000 eggs. Not all survive, but enough live to breed again, ensuring that the horde extends their range. With an average life span of seven years, and time to sexual maturity of 10-12 months, their population can dramatically shoot up in a very short time, which is precisely what happened once they landed in the islands.

“This is an invasion,” says Nitya Mohanty, a doctoral student at the Centre for Invasion Biology at Stellenbosch University (South Africa). His research, done with the Andaman and Nicobar Environment Team, has been on invasive species — first on the chitals (spotted deer) that have established their herds in the Andamans, and now on the bullfrog invasion.

So far, the bullfrog has been found in six out of the eight major inhabited islands. In 2017, it was even found in Little Andaman, which is separated from the Greater Andaman Islands by more than 55 km of sea. “This kind of incursion into remote islands is not naturally possible in such a short time,” says Mohanty.

The frog has acquired many names in the course of its journey through multi-cultural settlements of the island: shona beng (‘Golden frog’, for the prominent golden stripe) among the Bengali settlers; haramendak (‘Green frog’, for its olive-green skin) in Ranchi villages, where you could hear Oraon, Sadri or Munda being spoken; and dey-phala (‘Green frog”) in villages where the 2,500-odd Karen community stays. Whatever the name or language, the narrative of economic loss and ecological threat is a constant.

How they spread

Mohanty’s team sought to define the contours of this “invasion” through interviews with locals. As early as 2001, the bullfrog had already established breeding populations in one village. By 2009, it had spread to seven villages. Since then, at least 53 villages have reported the bullfrog in worrying densities.

Like most contemporary tales in the archipelago, the bullfrog story may also have to do with the earthquake and the tsunami that devastated large parts of Andaman and Nicobar islands in 2004. Following the decline of natural fish stock, the local administration encouraged integrated farming, with aquaculture in agricultural ponds. There are now over 2,500 such ponds in the islands, most of them filled with stocks of exotic, fast-growing fish imported from the mainland.

The fishling stocks (mostly from Kolkata) released into some of these ponds were contaminated with bullfrog eggs and tadpoles. All fingers point at the local fisheries department, which has, however, dismissed these claims and accused private traders of having brought the invader to the islands.

Most villagers believe that the bullfrog’s first hop into the islands was in Diglipur, in the northern tip of the Andamans, where its prolific spread first became a talking point. By 2011, it was spotted at Mayabunder in Middle Andaman, and by 2013, it was found in Wandoor, near the southern tip of the Andamans, around 300 km from Diglipur. While many were accidental releases, in some areas, it had been released by villagers as a fast-breeding cheap food.

Researchers Harikrishnan Surendran and Karthikeyan Vasudevan had been working in Wandoor since 2008, and were the first to report the presence of the bullfrog as an invasive in a scientific journal. “(The spread) is not surprising at all, given the high reproductive output of Indian bullfrogs and their association with agricultural areas… it was only a matter of time before they got introduced to other islands,” says Surendran.

Nearly two years ago, while engaged in construction and repairs at a resort near Wandoor in South Andaman, M. Alazhagan, 35, saw a multitude of frogs thronging the swimming pool. Some, he says, had turned yellow, with blue globules on their throat — males decked up for the breeding season. He approached one, and it froze. He decided to take a selfie: him grinning in the foreground, with the frog posing meditatively in the background. “It looked so strange! So much bigger than the frogs we were used to seeing and so colourful,” he recalls.

But fascination soon gave way to frustration. In North Wandoor village, located at the edge of the Lohabarrack Salt Water Crocodile Sanctuary, it isn’t the crocs that villagers keep an eye on.

The tsunami had created salty channels in the area and rendered large tracts infertile. So, many had turned to creating agricultural ponds — to rear fish and also because they would serve as sources of freshwater when the rains filled it up. Shushil Mondal found that his pond had been taken over by frogs. “Earlier I could get 20 kg of fish whenever I spread the net. Now, I get only shona beng. There is no fish left now. It has eaten everything,” he says.

The frogs pose a threat particularly to the livelihoods of landless labourers, such as Parimal Das and his family of eight. They had migrated to the Andamans from Kolkata nearly 20 years ago, and are now nomads, leasing land wherever it is available to grow vegetables. Agriculture in a rain-heavy, saline-rich soil is difficult, and free-range chickens are an important and steady source of income, with each fetching up to ₹600. “I’ve lost six chicks this year already. We had to build a murghi ghar (a wooden makeshift cage on stilts) to lock the chickens at night, but even then the frogs manage to squeeze through,” he says.

On the other side of the Greater Andaman islands, the Andaman Trunk Road snakes its way through dense forests. Trees form a seemingly impenetrable canopy, creepers drape branches in a gown of broad leaves, and undergrowth form layers upon layers above the damp soil. Amidst the shades of green, the Andaman Crape Myrtle, a deciduous tree, bursts in bouquets of small lilac flowers.

Five kilometres of these forests separate Gannatabla village — a settlement of Jharkhand tribals — from the nearest village in North Andaman. The village is a clump of 50 houses and a series of rectangular paddy fields. There is no pond here where fish is cultured. The bullfrog, however, lurks in these fields and drinking water wells.

Picture shows Gannatabla village at Diglipur in North Andaman.

Picture shows Gannatabla village at Diglipur in North Andaman.  
| Photo Credit: K. Murali Kumar


“We don’t know how it has come here. Three years ago, we spotted it in the streams that come through the forests when we went fishing for kala macchi (black fish). Now the fish is hardly seen but the frog is everywhere,” says 29-year-old Johnson Kirketa, suggesting that the bullfrog had crossed the forests through channels and streams.

Colonisers among the natives

Bullfrogs are found all over mainland India, but it is in the unique ecosystem of the islands that it becomes a major threat. Unlike the mainland, resources on the islands are scarce for big animals, while natural calamities are more frequent. The wildlife here has evolved in a miniature setting: there are no large herbivores (the largest is the Andaman wild pig) or large carnivores.

“Islands have fewer species, but their nature make them irreplaceable. They are found no where else in the world… This makes the entire food web in the islands very different from that of the mainland,” says Vasudevan, senior principal scientist at the Centre for Cellular and Molecular Biology, Hyderabad.

The Zoological Survey of India has found that out of the 9,130 marine and terrestrial species discovered so far in the islands, 1,032 species (or 11.30%) are endemic (found only in the Andamans). In the constraints of land, this endemicity increases to nearly 25%, or 816 out of the 3,271 land species. These creatures had evolved to cope with natural disaster, but have little capacity to withstand rapid, human-induced impacts. “There is not much room for redundancy and refuges in these islands,” says Vasudevan.

But the bullfrog is only the latest entrant in the Andamans’ 150-year-old history of invasives, with alien species introduced in waves by the British, Japanese, and ‘mainland’ Indians having gradually colonised many parts of the island territory. These include the elephant(introduced for logging and later abandoned), chital, hog deer, and barking deer (all three for game meat).

In 2013, using satellite imagery, Rauf Ali from the Puducherry-based Foundation for Ecological Research, Advocacy and Learning found that forests with elephants and chitals had suffered significant degradation (Interview Island) compared to places where they were absent (Little Andaman). It’s a one-two punch: elephants knock down trees and strip barks, while chitals prevent regeneration of forests by grazing on seedlings.

The Indian bullfrog

The Indian bullfrog  
| Photo Credit: K. Murali Kumar


Invasives have come in all forms to the Andamans. The Japanese introduced the Giant African Snail, one of the 100 worst invasive species as described by the International Union for Conservation of Nature (IUCN), in the 1940s during their three-year occupation. It has now established itself as a major agricultural pest. Meanwhile, about 90% of the fish being bred in ponds are carps and other exotic fish which have even established natural breeding sites outside human-created ponds. Similarly, the islands are home to at least 592 introduced alien plant species, some indirectly pushing endemic plants to the fringe.

Away from the obvious economic impact, it is in the sounds of the night that one can perhaps gauge the ecological impact of the invasive bullfrog. Across infested villages, residents say sightings of native species of frogs have reduced. Full grown natives pale in size to even a young bullfrog. Water snakes, a common accompaniment for the paddy farmer, and centipedes are in decline.

But even more worrying signs were found in the gut of the frog. For months, Mohanty and his associates captured and “stomach flushed” contents out of 798 individuals belonging to two native species and the invasive bullfrog. From the gut of the bullfrog came out native frogs, the endemic Andaman blind snake, the endemic emerald gecko, skinks and others. “Adult bullfrogs pose a threat to small endemic vertebrates (from frogs to birds). Within frog species, it can have a two-pronged impact on the Limnonectes genus of frogs. Bullfrogs not only eat the native frogs, even their diets overlap, indicating a possibility of competition,” he says.

It isn’t just their size that works to their advantage. It’s their appetite for meat, even at the tadpole stage. Bullfrog tadpoles are highly carnivorous, preying on other tadpoles (even native tadpoles) heavily.

Controlling invasives

In a few villages, the explosion in population from May onward sees a feast of bullfrogs: skin fried to a crisp, their legs boiled or fried. Here, a kilo (roughly three medium-sized frogs) is sold for ₹60 — the cheapest source of protein in the market. In other places, it is anger that has humans killing the frog. “Whenever I find it on the road, I beat it with a stick. If it jumps, I’ll jump into the paddy field and chase it. One dead frog means one lesser mother laying thousands of eggs,” says a villager in North Andaman, whose name has been withheld as killing bullfrogs is a criminal act under wildlife laws. In Wandoor, a family claims to have killed nearly 50 frogs in July.

However, these are mere dents in a burgeoning population. “It is difficult…I don’t see a way to stop it. The government should think of something. Else, in five years, poora basti bhar jayega (the village will be filled with frogs),” says Krishna Singh, at Mohanpur village in North Andaman, who claims to have lost 30 chicks to the frog.

Murmurs of the conflict have started, with the issue being raised by local political representatives. “It really is a big menace. But we have to see how the population stabilises,” says S. Dam Roy, Principal Scientist at the Central Island Agricultural Research Institute, Port Blair, which operates the local agriculture helpline.

Stung by the inflow of invasives, and with the fear that more could come, it was in the serene, undulating plantations that form the CIARI headquarters that a plan was hatched five years ago to start a ₹40-crore bio-security laboratory for quarantine and research. The plan did not materialise.

Globally, invasive species, particularly in islands, are becoming the focus of numerous organisations. The Convention on Biological Diversity has said that invasives have contributed to 40% of all animal extinctions since the 17th century. The IUCN has formulated guidelines for managing invasives specifically in islands, largely involving data collection, community engagement, policy measures and management plans.

Far away from the concerns of scientific papers and environmentalists, in the government offices at Port Blair, there is little panic about invasives. “They are just animals, and nature will find a way to live in harmony,” says Tarun Coomar, Principal Chief Conservator of Forests, who also holds the post of Environment Secretary in the relatively small administration governing the islands.

This confidence is not reflected among the villagers. While many are resigned to the invasion, some suggest commercial harvest for export to South-East Asia, for history has shown that animal populations crash when they have an economic value attached to them.

But for now, it is an unchecked invasion. “Bullfrogs have reached little Andaman, the next frontier is Nicobar. There are other islands they are yet to invade, and we must do everything to stop that. Signs at jetties about the adverse economic impact of bullfrogs and the need to check contamination of fish stocks could be useful,” says Mohanty.

For millenia, the islands, now a Union Territory, were largely disconnected, literally and figuratively, from the mainland. In more ways than one, the landscape here resembles those in Myanmar, Thailand and Indonesia than mainland India.

In ethos too, the disconnect remains. In government offices, officials caution outsiders (whose annual numbers touch 6.5 lakh, as compared to 3.9 lakh residents) to take it slow in the islands: “Ye mainland nahi, yeh Andaman hai (This is not the mainland, this is Andaman).” But it may not stay that way for long. As the croaks of the bull frog reverberate through the islands, their clamour assumes the urgency of a clarion call — to act before it is too late.


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