Rat makes its own poison to see off predators

Posted by Kate Taylor

A species of rat has developed the ability to defend itself from predators by smearing its body with a poison it makes itself.

The African Crested Rat, Lophiomys imhausi, gnaws on the highly toxic Poison-arrow tree and then slathers poisonous spit onto special absorbent hairs on its flanks.

While the poison is used by human hunters and can kill an elephant, the rat appears to be immune.

"At between 40 and 50 centimeters long, the Crested Rat looks quite innocuous as it clambers about in rocky, wooded valleys in Kenya and the Horn of Africa," says Jonathan Kingdon of Oxford University’s Department of Zoology.

"But once disturbed or attacked, the long fur on its flanks parts to expose a vivid black and white pattern around a leaf-shaped tract of peculiarly specialised hair, almost as if it is ‘daring’ a predator to take a bite of these poisoned hairs."

While the poisoned hairs are very close to the rat’s head, neck and thorax, these areas are protected with shields of bone, a reinforced backbone, and extra-tough skin.

"We observed the rat gnawing Poison-arrow tree bark directly from the plant, chewing it and then deliberately slathering the resulting mixture onto its specialised flank hairs," says Kingdom.

The hairs rapidly absorb the poisonous mixture, acting like a lamp wick.

The scientists have noi idea how the rat has come to be immune to the poison, ouabain - which has been used for centuries in tiny quantities to stimulate weak hearts. They hope that finding out more about the chemistry involved and the rat's genetics could lead to new medicines.