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Duttaphrynus melanostictus, the Asian common toad, is a stocky, warty-skinned toad of the family Bufonidae, native across South and Southeast Asia, from Pakistan through Nepal, Bangladesh, India, Sri Lanka, southern China and Myanmar to Laos, Vietnam, Thailand, Cambodia, Malaysia, Singapore and the Indonesian islands of Sumatra, Java, Borneo and the Natuna Islands. It was originally described in the genus Bufo.
Identification
Snout-vent length runs about 57-83 mm in males and 65-85 mm in females, making this a mid-to-large-sized toad with females noticeably bigger than males. The dorsal side is yellowish or brownish, with the raised spines and ridges running across it in black, and every individual’s wart pattern is distinct enough that researchers have used it for identification in field studies. The top of the head carries several bony ridges, and the eardrum (tympanum) is very distinct, at least two-thirds as wide as the eye. Behind the eyes sit a pair of prominent, kidney-shaped parotoid glands, the source of the toad’s chemical defence.
Habitat and range
This is a lowland generalist rather than a forest specialist: it occupies subtropical and tropical habitats up to about 2,000 m elevation, favouring disturbed settings such as forest margins, riparian areas, gardens, and agricultural and urban land over closed, pristine forest. Breeding happens in still and slow-flowing rivers and in temporary and permanent ponds and pools, while adults spend the rest of their lives on land, sheltering under rocks, leaf litter and logs and often gathering near human dwellings and street lamps at night, drawn in by the insects the lights attract.
Beyond its native range, the species has proven a persistent traveller. Introduced populations are established on Bali, Sulawesi, Ambon and Maluku, in parts of New Guinea, on the Andaman and Nicobar Islands, and in East Timor. Further afield, it reached the Madagascan port of Toamasina in 2011 and had spread across roughly 100 square kilometres by 2014, prompting comparisons with the cane toad invasion of Australia, and it has turned up at least four times in Australia itself since 2000, arriving as a stowaway rather than establishing there.
Behaviour and breeding
The Asian common toad is nocturnal, spending daylight hours hidden under rocks, leaf litter, logs and human-made structures before emerging to hunt. It is an opportunistic insectivore, taking earwigs, grasshoppers, crickets, beetles, wasps, bees, ants and termites, along with mollusks and terrestrial worms, and is often seen under street lamps when winged termites swarm.
Breeding is tied to water and, in seasonal parts of its range, to the monsoon. Males call to attract females with a melodic, repeated croaking, and during mating a male grips the female with the help of a subgular vocal sac and black nuptial pads on his inner fingers. A female lays her eggs in long strings on submerged vegetation, with a single clutch numbering around 40,000 eggs and no further parental care afterward. Eggs hatch within 24 to 48 hours, and the tadpoles that follow show a striking flexibility: those raised alongside siblings metamorphose faster than tadpoles kept in mixed, unrelated groups, and when predators are detected in the pool, tadpoles can cut their own body mass by as much as 46% and metamorphose earlier to escape the water sooner. Toads in the wild typically live around 4 years, against as much as 10 years in captivity.
The parotoid glands behind the eyes secrete a milky white bufotoxin that makes the species unpleasant, and potentially dangerous, to eat: it is toxic enough to cause illness or death in humans who ingest it, and snakes and birds are its main natural predators despite that defence. In places where it has been introduced far from its native range, predators with no evolutionary experience of the toxin are at greater risk from a mistaken bite.
Conservation
The facts box above carries the species’ current IUCN Red List category, Least Concern, reflecting its broad native range and tolerance of disturbed, human-altered habitat. That same adaptability is a liability elsewhere: the Madagascar population’s rapid spread since 2011 has drawn direct comparisons to the cane toad’s invasion of Australia, and repeated detections in Australia itself have been described as a risk potentially more damaging than the cane toad should the species ever establish there, since native predators outside its home range have not evolved resistance to its toxin.
Similar species
Within its native and introduced range, the Asian common toad can be confused with other warty, ground-dwelling toads, and Wikipedia’s article on the species carries an explicit warning not to confuse it with the Asiatic toad or the Asian giant toad, two distinct species that share part of its range. The bony ridges on top of the head, a tympanum at least two-thirds the width of the eye, and its distinctive black-tipped warts are the more reliable field marks, since overall size and colour vary considerably between individuals and populations.