If you’ve ever wondered what it might take to upset a microscopist, just ask James—our master of microscopes—his feelings about tardigrade legs.

Yes, tardigrade legs. Those chunky, wiggly limbs that move their owner through meals of moss and fields of debris.

What could possibly be in question when it comes to tardigrade legs? Why would such a seemingly mundane detail of the invisible world around us become a repeated point of contention in Journey to the Microcosmos meetings? The problem lies in the macroscopic world, specifically in the myriad of stuffed tardigrade toys available for purchase and the fact that many of them seem to have a fact-checking problem.

Take a moment right now to count the number of legs you see on this tardigrade. You should have hopefully counted four pairs, making for a grand total of eight squirmy limbs on our little water bear friend. But unfortunately, many tardigrade toy manufacturers seem to have stopped a little short in their counting.

While there are eight-legged tardigrades for sale, you’ll also find plenty of spurious ones that have only six legs. So to this day, if the question of whether we should produce our own Journey to the Microcosmos tardigrade merchandise comes up—including our t-shirts—James is the first to remind us that it would be an opportunity to correct the record in some small way. Now if you have also spent your life thinking of tardigrades as six-legged creatures, don’t worry—we have made the same mistake and have had to correct previous videos where we described them as having six legs.

Now we’re not quite sure what it is about these creatures that confuses their watchers in this way, but we are all in good company because the question of just how to count tardigrade legs has been around since their discovery. And it’s not the only quality of tardigrades that has inspired disagreement. This creature has been confounding us for centuries.

And while sometimes the scientific stakes have been low, at other times, they have been much much higher. The tardigrade was first described by Johann August Ephraim Goeze, a preacher in his 40s who had only just begun his microscopy hobby. But the beauty of the microcosmos is that it can reveal itself to anyone willing to look, regardless of experience.

And in 1773, Goeze would put the experience of watching a tardigrade into words for the first time. He said, Strange is this little creature, because the whole organisation of his body is extraordinary and strange and because his external appearance, at the first sight, has the closest similarity to a little bear. Goeze called his strange creature “kleinen Wasserbärs” or “little water bear,” a name that has stuck as a nickname for the tardigrade.

And about his little water bear—which he also at times called a worm—he said, The most remarkable feature of this little worm are the eight short feet, each of which is armed with three crooked and very sharp claws. But while Goeze’s publication was the first to describe a tardigrade, it would not be the only one for long. Within a few years, three other scientists would document their observations and inferences on the unusual creatures found swimming around in duckweeds and rain gutters.

Those scientists Johann Conrad Eichhorn, Bonaventura Corti, and Lazzaro Spallanzani. These papers were likely written independently of one another. And some of the features they described didn’t line up—particularly the legs.

Eichhorn drew a figure with ten legs, though we don’t know where he got ten from. Meanwhile, Spallanzani described a creature with six legs, though that seems to be due to the fact that he considered the last pair of tardigrade legs to not be legs at all, but instead of a pair of hooked filaments. Of course, a few mistakes here or there do not prevent one from making important contributions to our collective knowledge.

And one of the most lasting contributions of Spallanzani was the fact that he called these creatures “il tardigrado,” which translates to “sluggard” or “slow walker.” Of course, that name has since shifted into what we now call “tardigrade.” It’s not quite clear to us how the consensus that tardigrades have eight legs was settled. In 1785, a posthumous publication written by the Danish naturalist Otto Friedrich Müller established the correct number as eight. And a translator of Spallanzani’s work—a man named John Graham Dalyell—wrote in the footnotes of his translation about a species he’d found himself and named Tardigradus Octopdalis, better known as “the tardigrade with eight legs.” So at some point, toy manufacturers aside, there was an agreement that tardigrades have eight legs.

Not six. Not ten. Eight.

It appears to have been a relatively low stakes and low key argument in the world of tardigradology. After all if you can just look at them and be like, see, count, there's eight. Then, it's fairly easy to settle the argument.

But not all arguments have been that way though. In the middle of the 19th century, a 156 page report was written by Pierre Paul Broca, a French physician best known for his research on the brain. So why was Broca writing about an eight-legged, slow-walking microscopic creature?

Well, he was there to settle an argument—an old one—that gets to the core of tardigrades and their remarkable capacity to survive. Today, we know that water bears and many other microscopic animals are able to survive extreme conditions of heat or dryness by draining themselves of water, desiccating into a husk that essentially puts their life on pause until conditions become tolerable again. We know this process today as anhydrobiosis.

And it was first described in tardigrades by Bonaventura Corti, who had observed rotifers and other creatures going through it as well. But as more scientists documented the anhydrobiosis of tardigrades, more questions began to form around just what anhydrobiosis was. Was it death?

A state of pause? To answer that, tardigradologists had to agree on something even more fundamental: could tardigrades and their fellow dried out creatures live past anhydrobiosis? After all, logic and experience suggest that voiding oneself entirely of moisture is not a sound survival strategy.

On the one hand, there were experiments carried out by Spallanzani and others that seemed to demonstrate the conditions necessary to make anhydrobiosis a state that tardigrades could resuscitate themselves from. But others did not believe this kind of resurrection was possible. And in their quest to explain what others were seeing, some very creative alternative explanations popped up.

For example, the eminent naturalist Christian Gottfried Ehrenberg believed that people were actually seeing were the descendants of the dried out animal emerging from the husk of their great-great-grandparent. And in 1859, this led to the involvement of the Société de Biologie in Paris. A commission was called to settle the debate as presented by two French scientists.

On one side was Félix Archimède Pouchet, who believed that tardigrades could not be revived from anhydrobiosis. On the other side was Louis Michel François Doyère, who had documented his tardigrade resurrection experiments in his dissertation titled “Memoire sur les Tardigrades.” I'm sure you're all so happy to hear my French pronunciation. Both sides documented their experiments, and the commission performed control experiments, resulting eventually in the report written by Paul Broca that stated that Doyère was correct: tardigrades that go through anhydrobiosis can, in fact, be brought back to life from that state.

Of course, settling this debate only opened the door for more—for questions that we are still trying to answer about the mechanisms that allow tardigrades to survive anhydrobiosis and the limits to their resilience. But that is the joy of science, the way that disagreements compel us to strengthen our own arguments, to seek out the tools and experiments that will help us better understand the world around us. And perhaps, on that note, we should end with something that we hope we can all agree on as fellow hitchhikers through the microcosmos.

It’s a note from Goeze’s 1773 paper where he first described the little water bears that he had found. Surely, there is no greater pleasure than to see the polyps, the rotifers, and other beasts of prey under the magnifying glass seizing and swallowing their prey. This can be achieved without traveling long distances, without risking one’s life, and without big costs.

A glass lens shows us a new world, and I know from experience that you will be full of amazement, when seeing that for the first time. Thank you for coming on this journey with us as we explore the unseen world that surrounds us. We love diving into history here on Journey to the Microcosmos, but it’s important to remember that “History” is not just the same thing as the past.

The past is everything that has ever happened, history is the curated story of all the important events. But who gets to choose what’s “important” and what influences that decision? Well, “Study

Hall: US history to 1865” seeks to explore these questions as they cover American History from the earliest Indigenous groups to the Civil War. So, if you’re sitting there, craving a bit more history today, you can head on over to youtube.com/studyhall or the link in the description to watch “Study

Hall: US history to 1865” The people on the screen right now, they are our patrons on Patreon, and we're so grateful that they give us the opportunity to dive deep and learn about not just what we know now but how we came to know it. That for me, is the most interesting and more special thing about science. Which is not, a body of information that just appeared somewhere. It is all stuff that human beings figured out.

So thank you so much to all the people on the screen right now, for helping us tell these stories. If you want to see me from our Master of Microscopes, James Weiss, you can check out Jam and Germs on Instagram. And if you want to see more from us, there's always subscribe button somewhere nearby.