If you are not a fan of rodents, look away now. A giant rat – as big as a small dog – has been discovered living in the remote misty grassland mountains of Papua New Guinea.
This mighty mouse is around 65cm (25in) long, excluding its tail, and weighs 2kg (4.4lb). Add in the tail and you have an animal of 85cm (2.5ft) in length. Something your average farm cat would find rather daunting if it turned up in the grain store, let alone burrowing under your house.
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Previously, the existence of Mallomys istapantap, the Subalpine Woolly Rat, was only known through local tribespeople’s stories, occasional glimpses of a living rat by visiting research students and isolated dead specimens preserved in museum archives. Although the chubby rodent was described for science in 1989, it had rarely been seen by scientists in the wild, and certainly not in the past three decades, and it had never been photographed.
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This is strange when you imagine technology would have been advanced enough in the late 80s for researchers to document physical evidence through the use of camera traps. But it is a measure of how elusive and publicity shy this giant herbivore is. Only recent efforts on the part of biologist František Vejmělka of the Czech Academy of Sciences, have revealed the characteristics and behaviour of the massive murine.
Somewhat of a rat enthusiast and expert, Vejmělka spent six months assisted by members of several tribes living on Mount Wilhelm, Papua’s highest mountain. In that time he recorded and genetically identified 61 species of non-flying mammals, rodents and marsupials, including the subalpine woolly rat. “If it weren’t for the indigenous hunters who accompanied me in the mountains and helped me locate the animals, I would never have been able to collect this data,” he says.
Vejmělka took biometric measurements of the male rats he was able to catch in live traps, recording details of their cone-shaped heads topped by small round ears, their dense fur, sharp teeth, large 7.5cm (3in) paws and the parasites that live on them. He observed what plants they were eating – which turned out to be mostly ferns – and he watched theirnocturnal movements as they climbed up and down trees. During the day he saw how theysheltered in burrows or high in the tree canopy.
Although the rats are likely to have lived and evolved in Papua New Guinea over thousands of years, scientists believe their origins lie in more continental mainland areas. In Papua, however, they found a haven they could colonise in safety. “Their ancestors arrived from Asia to the island completely absent of any other terrestrial placental mammals (only marsupials and monotremes),” says Vejmělka. “The species’ large size is likely due to ‘insular gigantism’, a biological phenomenon in which animals on islands evolve to become larger than those on the mainland.”
Most importantly, during the course of his six-month study, Vejmělka took valuable footage of the rats going about their daily lives for future researchers to study. The hope is that highlighting the uniqueness of the mountain fauna will encourage local inhabitants and landowners to protect the animals’ vital habitat, in particular from the growing threat from mining companies.
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Credit: František Vejmělka, originally published in: Vejmělka, F. (2025). First scientific observation of the largest Sahulian rodent, Mallomys istapantap, in the wild. Mammalia.
