Loud and Clear: Bullfrogs of India

The sky was overcast, and the clouds looked like they would burst open any minute. My colleagues and I were prepping to step out to search for frogs in Someshwara Wildlife Sanctuary at Agumbe, Karnataka. Having gulped down hot, sugary tea, we put on our damp shoes and raincoats, which could barely keep water off, and entered the slushy trail. We could already hear frogs croaking along the trail, but a particularly loud call caught our attention. It was a deep, almost nasal-sounding “baamp...baamp...baamp...” that seemed to originate at the pond’s edge. Carefully, we stepped closer only to hear a loud “plonk”— the frog had jumped into the water and was gone. Looking around, we found at least five other Indian bullfrogs (Hoplobatrachus tigerinus) calling from the water’s edge before moving into the adjacent forests.

The bullfrogs belong to the genus Hoplobatrachus which comprises five species of frogs from sub-Saharan Africa through the Arabian Peninsula, India, Sri Lanka, and parts of Malaysia and China. Species in this group of frogs are all relatively large and muscular. They appear to be well armoured, and that’s perhaps why they are named Hoplobatrachus from the Greek word “hoplo” or armour and “batrachus” or frog. India has two species of bullfrogs: the Indian bullfrog and Jerdon’s bullfrog. Both are seen across the country, the former more than the latter. They are found in aquatic and semi-aquatic habitats including ponds, lakes, reservoirs, and waterlogged paddy fields. 

Indian Bullfrog

The Indian bullfrog used to be the most widespread frog species across India, though the common toad appears to have now taken that position. Bullfrogs are the largest frog species in India, growing to about 12 cm. We may encounter them during the monsoon around stagnant waterbodies. Typically, the individuals are dull brown to pale green and have skin folds on their back. The back (dorsum) is covered with small oval patches of black. Their hind legs are strong, helping them leap considerable distances and have stripes running across them. Perhaps this is why their scientific name is “tigerinus” (Latin for tiger-like stripes). Indian bullfrogs have an upright stance and hold their head high above the ground.  

Indian bullfrogs live at elevations up to 800 m in parts of the Himalayas and Bhutan, and further south, they are present in the Western and Eastern Ghats. Although they are often solitary, during the monsoon months, they often congregate in large numbers, anywhere between 20-50 individuals, and start vocalising. The males of this species dynamically change from green to bright yellow during the breeding season and are rather conspicuous. A pair of large, cobalt blue-coloured vocal sacs are visible when they vocalise. Unlike most other frogs, these adults start calling during the day. The males squabble a lot and jump on each other as they scramble for a mate. Once the female allows the male to mate, she hops around for a while and lays eggs in the water. The eggs develop into tadpoles in about a week.

Jerdon’s Bullfrog

Jerdon’s bullfrog (Hoplobatrachus crassus) is about the same size as the Indian bullfrog but appears slightly elongated compared to it. The body colour varies from pale yellow to olive green, with white undersides. The sexes are similar in colour, but juveniles may have spots and stripes on their legs and could be confused with the Indian bullfrog. They are solitary creatures that call from the water’s edge in the late evening and through the night. Their call is loud, rather deep set, with a variable number of notes, almost like a bleating goat. Little else is known about this species, predominantly found across South India, with a few rare records from Gujarat. Studies also indicate that the tadpoles of this species could tolerate salinity more than other frogs.  

Voracious feeders

Even as tadpoles, these frogs are voracious feeders. Both in the wild and in captivity, they consume tadpoles of other species and their own kind. The adults eat other frogs and are known to eat small snakes too!

The voracious appetite of the Indian bullfrog is harming other native frogs on the Andaman Islands, where they were introduced from the mainland. On mainland India however, they do not appear to be doing well. Historically, they have had an infamous reputation for being a gourmet delicacy, and until the 1980s, they were rampantly caught and exported. These frogs were also caught and killed for dissections in science laboratories. Fortunately, both the trade of frogs and the lab dissections of frogs are banned in India. With the ban on frog leg trade, the trade shifted to Southeast Asia and the numbers stabilised in India. However, despite the ban, the forest department sometimes catches people illegally capturing and transporting these frogs for local consumption.  

Disappearing frogs

Although these frogs were once abundant, they are increasingly becoming rare. Perhaps this is due to the decimation of populations for human consumption. It is also likely that suitable habitats where these frogs thrive are becoming rarer. However, the Indian bullfrog is still easily found in the Western Ghats, while Jerdon’s bullfrog is common in the drier landscapes of South India.