Pint-size pets were practical, once upon a time. A hunter using a wolf-like dog to ferret out game would bring home less bacon than one who used a terrier for the same tracking services.

Presumably, small hunting dogs mating with dust-mops is what gave rise to Shih Tzus and other foofy mini-dogs, which sadly are no longer in high demand now that Roombas can do the same job for cheaper.

Recently there was a “teacup mini-pig” craze, but we but dumped them when they turned out to be ordinary piglets which would soon outgrow teacups, buckets, and bathtubs. Now it seems the doe-eyed emoji supply is being squandered on “teacup dogs,” which require nothing more than a pocket protector as a kennel, a few grams of food per year, as well as a second mortgage to cover vet costs.

In spite of global condemnation, oil-rich pretend-princes and others short on life purpose are still driving the demand for micro-dogs as fashion accessories. As Wendy Higgins, EU Communications Director at Humane Society International points out, “It’s unnatural for dogs to be so small, so they often suffer from fragile bones and even organ failure. If you care at all about dogs, the very worst thing you can do is buy a teacup puppy.” But if interest in ever-tinier pets continues apace, I know of one that could set the diminutive limit. Move over, teacup pets – water-bears, also known as moss piglets, are more like teaspoon animals.

These Lilliputian livestock, which measure only 0.9 to 0.3 mm (or in non-metric terms, wicked-small to crazy small) long, are often called by their Phylum name Tardigrade, meaning slow stepper. Just because they are tiny does not mean they are short on character and beauty. Their expressive wizened faces, plump, fuzzy bodies and complex behaviours make water bears seem more like an invention of the 1960s psychedelic counterculture (articles have suggested they would be at home in Alice in Wonderland) than a diverse group of near-indestructible animals.

Water bears have four pairs of stubby legs, each terminating in 4 to 8 claws. Their bodies can be transparent, white, red, orange, yellow, green, purple, or black. Comprising more than 1,100 species, Tardigrades eat moss, lichen, algae, and occasionally, each other. Most of the time, when an organism is said to be distributed “worldwide,” that is shorthand for “widely.” Not so with these critters. In addition to being the “other polar bear,” they are found in the deepest ocean vents, hottest mud volcanoes, driest deserts and throughout ice sheets and glaciers.

Moss piglets/ water bears are all-around tough, maybe more so than any other life form. Many biologists have remarked that Tardigrades could survive another mass-extinction such as historic ones caused by massive meteor impacts. But to be a true extremophile, an organism must do better in harsh conditions than in average ones. While water bears can survive almost anything, they really prefer the same cushy sorts of things most humans do: enough air, water, food, and temperate conditions.

“When the going gets tough, the tough get going,” which I always assumed meant to someplace quieter. When life gets challenging for a water bear, it forms a cryptobiotic state known as a tun, draining nearly all the water out of its cells and replacing some of it with a sugar called trehalose. It also produces a special damage-suppressing protein to protect against DNA damage. How much tougher are moss piglets in this state? Tuns.

Whereas about 500 rads of X-rays would kill a human, 570,000 rads did not seem to cause mortality or even DNA damage to these things. Tardigrades have been demonstrated to live for 20-30 years in their cryptobiotic form, yet after a few minutes of hydration, continued to function normally. I’ll bet some even pick up the thread of their last conversation.

According to a report in Smithsonian, they tolerate cold down to about -200C (-328F), close to absolute zero. And I’m not sure how one would cook water bears, because they also live through 149C (300F), which is a pretty hot oven. Tardigrades can withstand more than 1,200 times atmospheric pressure, as well as the complete vacuum of space – in 2007, some were taken into low-Earth orbit for 10 days on the Foton-M3 spacecraft.

The cryptobiotic strategies of water bears have allowed doctors to develop so-called dry vaccines based on trehalose instead of water. These are not subject to spoilage, a benefit to people in regions where refrigeration is limited.

In addition to the animal-cruelty angle, another drawback to teacup dog ownership must be the flavour of tea, I would guess. Fortunately, tardigrades are born paper-trained. Each time a water bear grows a bit, it has to shed its skin or moult, a process which may be repeated 12 or more times as it matures. Masters of efficiency, they wait until they need to moult before pooping, and leave rows of little pellets lined up inside the old skin. This would make it handy for their owners to pick up when taking their charges to the water-bear park, should such a thing ever come to be. Lifespans vary by species from a few months to a couple years, not counting time spent in suspended animation.

Water bears can be collected from nearly any substrate, especially moist ones like moss, at any time of year, and viewed with a hand-lens or low-power dissecting scope. Because water bears are too small to work even as cufflinks, these naturally tiny critters may not satisfy those who seek living fashion accessories. Please help promote ethical pet ownership — avoid teacup pets, and adopt a tardigrade!

Photo of SEM image of Milnesium tardigradum in active stat courtesy wikimedia user Daniel Mietchen.