Until I watched Star Trek: Discovery in this latest lockdown, I’d never heard of a tardigrade. But when I learned that the super-sized, space-travelling monster on screen was inspired by a real-life micro-animal, I had to see one in the flesh.
There are over 1,000 known species of these intriguing invertebrates, and as they thrive in mosses, lichens and liverworts, finding them in the garden was reputedly a relatively easy task.
The cushion moss growing on my greenhouse roof was the most likely looking habitat, so I peeled off an emerald green clump and squeezed the liquid straight into a Petri dish.
Shining a light through the side of the container, I illuminated a nematode swimming circuits, and two springtails floated on the surface. But it was a slow-moving speck, less than a millimetre in length, that captured my attention. Observing with the naked eye, I couldn’t make out any distinguishing features, but once magnified, I could clearly see four pairs of stubby legs propelling a tubby, translucent-bodied creature through the mossy soup – I’d found a tardigrade! With its lumbering gait and ursine-like clawed feet, I could see why the zoologist Johann August Ephraim Goeze called them “little water bears”, though I prefer the alternative nickname, “moss piglet” – a reference to their snout-like mouthparts.
Despite their unassuming appearance, tardigrades are perhaps the most resilient organisms on Earth. They can withstand temperatures ranging between -272.8°C and 150°C, pressure six times greater than that exerted in the Mariana Trench, and ionising radiation at doses hundreds of times higher than the lethal dose for a human.
They have the ability to slow their metabolism to 0.01% of the normal rate, and unique proteins in their bodies “vitrify” during desiccation, meaning they form a glass-like cocoon that allows them to exist in suspended animation – known as the “tun” state – for decades, only reanimating on exposure to water.
Like their fictional counterparts, these extreme survivalists have been proven to endure the vacuum of outer space. In fact, following the crash-landing of the Israeli lunar lander Beresheet in 2019, it’s believed that the mission’s cargo of several thousand tun-form tardigrades may be strewn across the surface of the moon.
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• This article was amended on 5 February 2021. Due to an editing error, an earlier version erroneously said that tardigrades “can ionise radiation at doses hundreds of times higher than the lethal dose for a human”. This has been corrected to state that the organism can survive such doses of ionising radiation.