LEAN ON ME
The tiny forest-dwelling mammal with a super-strength spine
Ifirst heard the story of a legendary animal called the hero shrew (Scutisorex somereni) some time ago. Apparently, somewhere in the tropical African forests of northeastern Congo there lived a small mammal that could withstand being stood on by a 70kg human for five minutes at a time and remain unaffected by the ordeal.
Really? It seemed so fanciful and implausible to my enquiring and scientific mind. I mean, why would a small insectivorous mammal such as a shrew need to be so osteologically reinforced? It sounded made up, like something from Marvel Comics. It wasn’t until many years later, sitting around a campfire with an African mammalogist, that I began to realise there was some truth in these claims.
Most members of the shrew family are secretive and unassuming, and the hero shrew, at least outwardly, looks and behaves just like most shrews. It is a little larger and longer furred than you might expect (at around 25cm from the tip of its tail to the end of its pointy snout), but otherwise, there is nothing that remarkable about it
– a dull grey, timid, scuttling creature of the forest floor, certainly nothing heroic.
Even the first time a Western scientist ‘discovered’ the shrew in 1910, its uniqueness was overlooked. But the local Mangbetu people from northeastern Congo already knew the hero shrew was special; their warriors would even wear the dried corpses or parts of the shrew about their person as a talisman of strength and invincibility. It was the Mangbetu that had demonstrated to visitors how the shrew could be trodden on without ill effect.
Still, it wasn’t until years later when a scientist dissected a specimen that the reason for this phenomenon was discovered: it had the most unusual skeleton. Specifically, the lower lumbar region of the spine.
Think of the usual mammal backbone, comprised of a string of individual bones called vertebrae. Each vertebra is a relatively simple structure with three wing-like projections, called processes, and a variety of low bumps and lumps that
“It could be stood on by a 70kg human for five minutes”
serve as connections and anchor points for muscles, cartilage and tendons.
However, whereas the lumbar region of humans comprises five vertebrae, the lumbar of the hero shrew has 10 to 11, each bedecked with so many processes, bumps and lumps that they look like something between a Henry Moore sculpture and a Romanesco broccoli. The result is a spine that is four times more robust than any other mammal for its size.
The big question that remains, though, is what’s it for? There isn’t any particular predator that the shrew needs to fend off. It has been hypothesised that it needs to hold its body off the sodden, seasonally wet forest floor, but this seems unlikely.
The best explanation, for me, is one of leverage. The shrew is often found around the bases of palms, where it forages for large beetle grubs that live between the leaf scales and the trunk. For an insectivorous mammal, each finger-thick grub represents a seriously valuable meal. So maybe the reason behind the hero shrew’s superpower is that it becomes a living crowbar, jimmying the bases of the palm leaves apart, even shoving its way under fallen logs and leaves with a single flexion of its spine to get to this rich source of food.
Shrews have other superpowers, too. Some temperate species can shrink their skeletons and brains to save energy during the winter, and some shrews, including water shrews, are one of only three groups of mammals with a truly venomous bite.