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Official magazine of the Biological Sciences Society
National University of Singapore
The Mudskipper, Jul 94
Four Favourites

by Kevinsky Humchnek & Sivapithecus

A limited issue of MRT cards issued recently typically depicted exotic frogs. Sigh! Local fauna takes a beating yet again. Consider the case with which you can buy loads of good South American rainforest t-shirts in departmental stores, but struggle to find one relevant to Southeast Asia. Nearest source is probably a C. L. Chan t-shirt at the office of the Malayan Nature Society in Petaling Jaya, Selangor! [He's the guy who designed all those colourful T-shirts featuring Sabah, Mt Kinabalu and Sepilok Orang Utan Rehabilitation Centre.]

But we digress - back to the MRT cards. The frogs were probably chosen for their beauty. Given four choices, which species of frog or toad would you nominate as Singapore favourites (or should we say, 'froad'?). We wondered if most of the BSSers would choose something colourful, strange looking, or endangered. We decided to vote for species that would never have made it to MRT cards, but have an interesting background and are familiar to us all. We'll leave it to you to choose the more traditional candidates for public affection...
asian toad in a bottle
1. Asian Toad
(Bufo melanostictus)

This species is the subject of enthusiastic hunts by JC biology students who are requested to procure their own specimens for "frog dissection". The peak period of the hunt is traditionally the night before the actual practical itself. Enterprising students who anticipate the squeamishness of classmates make a quick buck by selling surplus material at inflated prices. These individuals never do their dissections properly and subsequently pursue a career in commerce.

Distinguished by dry-looking, rough, warty skin and two particularly large "warts" (paratoid glands) behind the eyes. These glands can secrete an irritant fluid which may help repel predators. Remember your mother's warning? It is generally safe to handle toads with bare hands as long as contact with this fluid is avoided. Reaches to about 10 cm in snout-vent length.

Toads often inflate themselves up when disturbed or when they feel threatened. This makes them appear larger and bulkier, and thus quite a mouthful to potential predators. Some people mistake this behaviour as an intention to blow poisonous gas into their faces! While not preyed upon by many animals, you have probably seen the thin and crispy remnants of a flattened toad well-baked by the sun alongside a road.

Probably the best-known and abundant amphibian in Singapore. Widely distributed in Southeast Asia. Found usually in association with human habitation. Terrestrial, lives in places such as gardens, grass lawns, football fields and scrubland. Active mainly at night, but may become aroused in the event of a heavy downpour.

Spawns usually after heavy rains in drains and puddles, females lay long gelatinous strings of eggs. Tadpoles are small and black. Feeds mainly on insects, often congregate under street lamps at night to feast on insects attracted by light. Generally of no commercial value, except to enterprising biology students.

painted bullfrog bellowing2. Painted Bullfrog
(Kaloula pulchra)

Recall the bellowing you associate with wet nights? Probably the most frequently imitated animal call in the Ecology lab, the loud sound is believed by some to be amplified by the acoustics of monsoon drains around which this frog seems common. But take no credit away from Kaloula; they are loud in their own right. During and after heavy rains, the males make their way to puddles of water, or monsoon drains where they inflate their bodies and start to call to attract females to mate with. The call sounds very much like the bellow of cattle, and can carry over long distances.

Distinguished by superficially smooth skin, rounded appearance, small head and coloured brown with two yellow or beige stripes on both sides of the back. Snout-vent length to about 7.5 em. It tends to burrow into soil, or hide under objects and litter in the day, appearing at night to hunt for insects. The tadpoles are rather transparent, dusted with gold specks and the tail is reddish in colour. They are usually found in quiet water bodies, suspending almost motionless in mid-water, but making short darts when disturbed.

Found mainly in Indo-China, the frog is said to have "followed" man from northern Malaysia down south to Singapore. Like the Asian Toad, it is associated mainly with human habitation, occurring in gardens and public parks, construction sites and school fields. It sometimes wanders into houses. Common, but probably due to its secretive nature, does not appear to be as familiar as the toad. Probably most frequently unearthed during the intensive hunts by biology students for dissection specimens. It is ironical that these frogs are almost always rejected by students in favour of the more compact and less-slimy toads for the purpose of their "frog" dissection practicals. Note that Kaloula bears no relationship to the drink frequently imbibed by certain individuals on the floor of S2-02.

crab eating frog eating crab3. Crab-eating Frog
(Rana cancrivora)

Famous for crab-eating and its osmoregulatory capabilities. Crabs do form a part of its diet as it lives in coastal areas and penetrates brackish water, but it also eats almost any other animal that is smaller than itself. It is also not the only frog which feeds on crabs. For an explanation of the physiological mechanisms that help it venture into brackish water, wait until this year and Prof. Lam will reveal all. It is, however, not alone in possessing this special ability among amphibians. Tadpoles of the Asian Toad hive also been found in brackish water.

Grows over 8 cm in snout-vent length. Found mainly in coastal areas, usually in the vicinity of human habitation. It is common, inhabiting farmlands, fields and marshland, sometimes inside mangrove swamps and in prawn ponds. Distinguished by rough skin with longitudinal ridges on the back, broad head and muscular hind limbs. Brown above with irregular blackish blotches on the back and limbs, a yellowish stripe on the sides.

It is sometimes sold for food, as it grows to a large enough size, and the bind legs are muscular enough. If you've been to the farms near Sungei Buloh, you may see large numbers of its tadpoles being raised in net-covered ponds. The newly-metamorphosed froglets are collected and sold to aquarium shops as live food for arowanas and other large predatory fish such as snakeheads. It is also a candidate for dissection classes.

The males can be detected at night by their calls, which resemble a chuckle. If you're hunting them unsuccessfully, they seem to be mocking you. The tadpoles are mottled with different shades of brown, and blend in with the mud substrate of roadside puddles and ditches where they are often found. The Field Frog (Rana limnocharis), which is also common and sometimes coexists with the Crab-eating Frog, is similar in appearance, but has a narrower head, less extensive webbing on the hind foot and is less bulky and smaller in size (6 em). It has a chirping call and does not tolerate salt water.

american bullfrog about to be lunch4. American Bullfrog
(Rana catesbeiana)

A common frog in Singapore, but seen usually in the wet market where they are sold for culinary purposes. It grows to a rather large size, at least 12 cm in snout-vent length, and has muscular hind limbs. It is green on the head, greenish-yellow on the back and limbs, with brown blotches.

It is bred commercially and locally (or in Malaysia?) in frog firms. It can have a rather voracious appetite, and eats almost any animal smaller than itself. Examples of this North American native have been seen along the shores of reservoirs where they have been released well-intentioned individuals, highlighting a common problem. Many people release animals into their local habitats without considering the outcome of such action. There have been many instances in which exotic (foreign) species of plant or animal thrive at the expense of local species. Some animals just die since they can only survive in captivity, or can't cope in a foreign land. Controversy surrounds even reintroductions programmes conducted by wildlife and scientific institutions based on the biology of the particular animal and the habitat which was part of its former range.

You may, however, rest assured that so far, there have been no signs to indicate that this alien species can survive in the wild state here.
© N Sivasothi, 2001