Tardigrade Three-Way Caught On Camera In Steamy Microscope Footage

"We saw you from across the petri dish and really dig your vibe."


Rachael Funnell


Rachael Funnell

Digital Content Producer

Rachael is a writer and digital content producer at IFLScience with a Zoology degree from the University of Southampton, UK, and a nose for novelty animal stories.

Digital Content Producer

tardigrade threesome

In a rogue move for threesomes, the tryst started out with some poop signalling. Image credit: DataBase Center for Life Science (DBCLS), CC BY 4.0 via Wikimedia Commons / aquatti / / IFLScience

Group sex isn’t uncommon in the animal kingdom, but when you’re dealing with microscopic subjects, capturing it can be easier said than done. Fortunately, scientists like James Weiss who constantly monitor microscopic beasties are primed and ready to record the magic as it unfolds, including a three-way between some tardigrades.

The rare and steamy footage involved two males who were seemingly drawn to a female as she defecated. Whether or not this helps her case in finding a mate isn’t known for certain, but briefly separating the trysting trio didn’t last long as the males both returned, indicating they could be detecting something in the water.


"In water, everything is about chemical cues, so males have to gather some information to find females," Weiss told Science Alert. “So I believe there's some chemical signaling happening, and well, pooping releases a lot of signals into the water.”

Whatever lured them in, the males both stuck at it for about 30 minutes before one moved on. The remaining male continued mating with the female for a further hour, making for quite the tape of tardigrade encounters.

Tardigrades have rich and varied sex lives, with some marine species being bisexual and exhibiting far more complex copulation behaviors than researchers expected. Studies have even found evidence for tardigrade foreplay as Isohypsibius dastychi were seen providing mutual stimulation that preceded semen ejaculation and egg deposition.

Parthenogenesis is also common among terrestrial tardigrades, and there are even some hermaphroditic species. As for how sex between two tardigrades goes down, it involves a male with spermatozoa stored in large testis ejaculating semen through seminal vesicles through the cloaca of a female. Investigations have even allowed us to visualize the cloaca, revealing it’s covered by a triangular pouch with one opening.


Males and females will copulate when there are unfertilized eggs available, sending the males into something of a frenzy while the females just sort of get on with things. The male will grasp on with the aid of little claws and wriggle until the job is done.

A remarkably complex performance considering these critters measure less than a millimeter. Despite their small size they’re incredibly hardy and have dominated a wide range of environments giving rise to their nicknames “water bears” and “moss piglets”. They’re also pretty much indestructible and have adapted to thrive in extreme environments like the deep sea, high altitudes, and sub-zero temperatures. They can also tolerate high levels of ionizing radiation and exposure to all sorts of chemicals that would kill just about any other life form.

As the saying goes, you work hard, you play hard.

[H/T: Science Alert]


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