Mammals
African Crested Rat
Lophiomys imhausi · also called african crested rat, maned rat, crested rat
The African crested rat is a large, slow, shaggy rodent of the East African highlands with a defence unlike any other mammal’s. It chews the bark of the arrow-poison tree — the same plant hunters use to tip their arrows — and licks the toxin into a strip of specialised, sponge-like hairs along its sides. A predator that bites it gets a mouthful of poison, and dogs have died from doing so.
Overview
The African crested rat lives in montane forest, scrub, and rocky country across the East African highlands, from Ethiopia to Tanzania. Head and body run 25–36 cm, with a bushy tail, and it weighs 0.6–0.9 kg. The long grey-and-black fur carries a mane of erectile hairs down the back. It is a nocturnal herbivore.
A borrowed poison
It gnaws the bark and roots of the arrow-poison tree, chews the material with saliva, and applies the toxic paste to a band of modified hairs on its flanks. Those hairs are unlike any other mammal hair — perforated and spongy, with an internal lattice that soaks up and holds the plant’s cardiac toxin like a wick. This is the only confirmed case of a mammal taking a poison from a plant to defend itself.
The warning
Threatened, the rat parts its fur to reveal a bold black-and-white flank pattern that frames the poisoned strip and directs a predator’s bite straight into it. The toxin is a potent cardiac glycoside, and dogs that have bitten a crested rat have become seriously ill or died.
Status
The African crested rat is Least Concern but poorly known — patchily distributed and naturally uncommon. Recent fieldwork found it lives in bonded pairs and family groups, a social pattern rare among rodents.
African Crested Rat: common questions
Is the African crested rat actually poisonous?
It is, but not in the way a venomous snake or a poison frog is. The rat does not make a toxin and has no venom gland. Instead it acquires poison from outside its own body, by chewing the bark and roots of the arrow-poison tree and transferring the resulting toxic slurry onto a strip of modified hairs along each side. Those hairs then carry a lethal dose of a plant cardiac glycoside. A predator that bites the rat gets that poison in its mouth. This behaviour, taking a defensive chemical from a plant and applying it to the body, is well known in insects but had never been confirmed in any mammal before this species.
How does it survive handling its own poison?
That is still being worked out. The toxin involved, related to ouabain, interferes with the pump that keeps heart muscle cells working, and a small amount can stop a mammal's heart, so the crested rat's apparent tolerance is remarkable. It may have changes to the molecular target that the poison acts on, similar to the resistance seen in some insects that eat toxic plants, and it seems to handle the material carefully, applying it to hairs rather than swallowing much. Researchers have observed rats chewing the bark and then grooming the paste into the flank hairs without obvious ill effect.
What is the crest for?
The long hairs that run down the back can be raised into a mane, and this is part of the animal's defensive display. A threatened crested rat hunches, erects the crest, and spreads the fur along its flanks to expose a high-contrast black-and-white stripe that runs the length of the body and frames the poisoned hair strip. The overall effect makes the rat look larger and advertises, in the manner of a skunk's stripe or a poison frog's colours, that this is an animal not worth attacking. If the predator ignores the warning and bites, its bite lands in the toxin.
Is the African crested rat dangerous to people?
Not if it is left alone. It is slow, docile, and not aggressive toward humans, and it will try to display and retreat rather than attack. The danger is in contact with the poisoned flank hairs, so it should never be handled with bare hands, and the toxin could be harmful if it entered a cut or the mouth. The main real-world risk is to pet dogs that catch one, which is why the rat has a reputation in parts of East Africa as an animal to keep dogs away from.