Some might think it's up there with the flying pig and the killer rabbit, in the list of improbable animals – the screaming tadpole. But it's real. 
 
 Scientists in South America have discovered that the larvae of the Argentine horned frog, a species remarkable for its tendency to try eating anything that passes, emit a "brief, clear and very audible metallic-like sound" when they feel threatened. 
 
 Horned frog tadpoles are naturally aggressive and carnivorous, often eating the tadpoles of other frogs, and it is possible that the scream is mainly emitted when another horned frog tadpole moves to attack it as a measure to avoid cannibalism. 
 
 The discovery, reported in the Swedish journal Acta Zoological, is the first evidence for the production of sound by the larvae of anurans (frogs and toads). It was made by Dr Guillermo Natale of the National University of La Plata in Buenos Aires, and his colleagues, when they were studying the mating calls and croakings of adult frogs. Many adult amphibians use loud sounds such as croaks to advertise their presence, and often to attract sexual partners but until now researchers did not realise amphibian larvae might also produce sounds underwater. 
 
 That changed when Dr Natale caught a horned frog tadpole in a pond using a hand-held net. "We heard a brief, clear and very audible metallic-like sound," he said. To investigate further, the researchers caught a wild pair of breeding adults, and began a programme to rear them in captivity. 
 
 The researchers found that when horned frog tadpoles come into contact with, or are prodded by, an external object such as a metal spatula, they let out a brief, metallic sound consisting of a short series of higher frequency pulses. The tadpoles produce the sound by pushing air out of their lungs, which develop very early; tadpoles that are just three days old are capable of emitting loud distress signals. The discovery raises the possibility that other tadpoles may produce sound. ||||| By Matt Walker 
 
 Editor, Earth News 
 
 Please turn on JavaScript. Media requires JavaScript to play. Advertisement Tadpoles of one frog species let out an audible "scream" when they come under attack, scientists have discovered. They only make the noise, described as a brief, clear metallic sound made up of a series of notes, when in distress. It is the first time any vertebrate larva has been found to use sound to communicate underwater. The discovery that frog tadpoles can make sounds also raises the possibility that a host of aquatic larvae communicate in a similar way. The distress calls are made by tadpoles of the horned frog Ceratophrys ornata which lives in Argentina, Uruguay and Brazil, researchers report in the journal Acta Zoologica. That tadpoles communicate somehow is simply amazing 
 
 Dr Guillermo Natale 
 
 National University of La Plata, Buenos Aires Scientist Dr Guillermo Natale of the National University of La Plata in Buenos Aires, Argentina, and his colleagues, were studying the mating calls of adult frogs. Many adult amphibians use loud sounds such as croaks to advertise their presence, and often to attract sexual partners. Until now though, researchers did not realise that amphibian larva might also produce sounds underwater. That changed when Dr Natale caught a horned frog tadpole in a pond using a hand-held net. Please turn on JavaScript. Media requires JavaScript to play. "We heard a brief, clear and very audible metallic-like sound," he told the BBC. C. ornata tadpoles are difficult to find in the wild, so the researchers caught a wild pair of breeding adults, and began a programme to rear the young amphibians in captivity. This enabled the scientists to better study the noise they had heard in the field. The team discovered that C. ornata tadpoles are naturally aggressive and carnivorous, often eating the tadpoles of other frog species that they encounter. However, "much to our astonishment, they do not eat each other," says Dr Natale, who is also an assistant researcher Argentinean Research Council (Conicet). That may be because of the "screams" emitted by the tadpoles. The researchers found that when C. ornata tadpoles come into contact with, or are prodded by, an external object such as a metal spatula, they let out a brief, metallic sound consisting of a short series of higher frequency pulses. FROG FACTS 
 
 Watch an 'alien scene' of feasting tadpoles The first truly monogamous amphibian was discovered this year Toads, close relatives of frogs, may be able to predict when an impending earthquake will strike Watch more videos of bizarre frog and toad behaviour here Each "scream" lasts for just 0.05 seconds. Producing distress calls is likely to help prevent the tadpoles cannibalising each other. Underwater call The tadpole produce the sound by pushing air out of their lungs. The lungs develop very early in this species; tadpoles that are just three days old are capable of emitting loud distress signals. They continue to emit distress calls underwater both as tadpoles and after they have begun metamorphosis (when they become froglets). The tadpoles also produce the sounds when they are removed from the water. In fact, when out of the water, they make the distress call more frequently. This could be because the tadpoles can more easily access air, which they then expel. An oscillogram show the pulsated structure of the tadpole's distress call with pulsated structure "That tadpoles communicate somehow is simply amazing," says Dr Natale. "They possess the structures to do so within 3 days of life." He and his colleagues now want to study how and why the ability develops so rapidly, and how the sound is perceived by other tadpoles. "[We want to know] what information specifically is communicated," he says. Few larvae of any animal species are known to produce sounds. Those that do tend to be insect larvae, which live on land, making their sounds into the air rather than underwater. For example, juveniles of one species of common silkmoth caterpillar (Antheraea polyphemus) make "clicking" sounds with their mandibles to warn off predators such as ants. A female adult horned frog But as far as the researchers can tell, horned frog tadpoles are the first underwater larvae, and first larvae of any vertebrate, to make sounds. The discovery could have far-reaching implications for our understanding of the behaviour and ecology of amphibians, many of which are threatened by disease, habitat destruction and illegal trade. "We have definitely underestimated their abilities," says Dr Natale. "In more than 200 years of [amphibian research] this has never been reported." 
 
 
 
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– Scientists studying the calls of adult Argentine horned frogs were amazed to discover that the species' larvae also make sounds—screams even, reports the Independent. The tadpole's scream is a "brief, clear and very audible metallic-like sound," say researchers. They believe the distress calls save the tadpoles from being cannibalized by adults of their species, which is known for its willingness to eat anything it can, including other kinds of frogs. This is the first time underwater larvae or any vertebrate larvae have been known to make sounds, the BBC notes. The researchers believe the discovery has wide-reaching implications for the understanding of amphibian behavior. "We have definitely underestimated their abilities," says the lead researcher, who now plans to study how other tadpoles respond to the sound.