It’s all so sudden.
The victim is on the left side of the screen—a single-celled little pulse of life, floating about in pond water somewhere. It’s got these little hairs called cilia. You don’t see them at first. They can turn into oars. Oars for escaping.
But it doesn’t know.
The killer comes in from the right, turning lazy circles in the water, like nothing’s going on. But that’s an act. As we’ll learn later, it is getting into position, moving close, finding an angle so it can point its … its what? I see no weapon. Does it have a weapon?
“I don’t know about this exact type of ciliate,” microbiologist Patrick Keeling wrote me, “but I know about other similar predators,” and at the very end of its snout-like appendage, it’s probably packing a bunch of “poisoned harpoons.” At nine seconds into the video, you can see it aim straight at the victim …
… There’s a shudder. The victim, which has been paddling along, suddenly gets smaller—much smaller—and stops moving. I saw no harpoon, but the water is muddy. If there is a needle, it would be very hard to see. “The poison,” Keeling figures, “causes paralysis where it hits.” But only for a beat.
Very quickly, the victim bounces back, gets larger, sticks out its cilia and begins paddling furiously, trying to get away. It’s beating so fast, its oars become a blur on its exposed side—but then comes the second blow.
This happens 15 seconds in; when I looked close, there’s a second snout, inside the killer’s body that grabs onto the victim, pulls, and fires. Is there a second dart? A bite? (It has no teeth, so it can’t bite.) But the victim now goes all quiet. The cilia disappear. This is a big catch. It would be like you or me eating an entire goat. “They eat by phagocytosis,” Keeling says. These small bits of pond life have cell walls, but those walls (if you’ve seen the 1956 horror pic The Blob, you know how this goes) can suck in and extend at the same time. The killer slowly surrounds, then pulls in its victim, like this:
Can it stuff everything in? Won’t it gag? No, biologist David Caron wrote me. “Our (human) perception is that food particles have to be a small fraction of our own size. Not necessarily true to many single-celled organisms which can expand their membranes quite a bit to accommodate large prey items.” (Really large. This victim is roughly half the size of its killer.)
Well, at least it’s still. I wouldn’t want one of those things jiggling inside me. But here’s the thing: The victim, now stitched into a sack of its own, called a vacuole, may not be dead. That other yellowish package, already floating in there, both biologists say, is a previous victim, now awaiting “further breakdown.”
“The prey is indeed alive when it gets eaten,” Keeling wrote. Does it stay alive?
“When a cell ‘dies’ is a hard question,” he says, “Some cells stay alive inside others for a long time, even after partially being digested.” There are single-celled creatures that feed on algae but leave the parts that turn sunshine into food—the chloroplast—alive and working for long periods.
So at the end of the video, neither Keeling nor Caron could say if the victim is dead. “Every food vacuole has its own processes … and its own timing,” Caron writes. It will die eventually, dissolved by acids, the unused bits flushed out. “Yes, essentially, they defecate,” Caron says, but how long that takes, we don’t know.
The victim, of course, has no questions. One moment it’s free, paddling about, then, in a flash, it’s shot, grabbed, swallowed, walled-in, and stuck. “What just happened?” it should wonder. But it can’t. Single celled creatures don’t wonder. At least I presume they don’t.
We do. Being three trillion cells bigger, we have the machinery to call experts, email videos, figure out motive, cause, possible weapon—and even, if you’re me, feel bad for the victim. This takes a lot of cells.
Not to brag, but when it comes to murders, this is an advantage we humans have over pond scum. It’s just better to be multicellular. (Unless you’re the victim. Dead humans and dead protozoa are pretty much the same—dead.) But alive, it’s people, not protozoa, who can enjoy a good murder mystery. That’s why my audience, small as it is, is (like you, I presume) entirely multicellular.
Thanks to the University of British Columbia’s Professor Patrick Keeling, who argued with me about my headline. He doesn’t think “murder” is the right word for what happened here. “I don’t think of it as murder,” he wrote me; it’s “more like hunting. I see it as being like the Serengeti on a small stage, where the lions and zebras all have their roles to play and there is no moral message in any of it.” I suppose that’s fair, but when I saw Wim van Egmond’s gorgeous video, what got me fascinated was how the killer killed. I couldn’t figure out how it did it. Having a very Agatha Christie reaction, I chose very Agatha Christie language. That, alas, is my excuse.
Thanks also to Professor David Caron at the University of Southern California, who on Christmas Eve watched the video and answered my questions so promptly, and to Elio Schaechter of the Small Things Considered blog, who told me who to call. And most of all, a pop of flashbulbs to Wim van Egmond, one of the world’s great microbiology photographers, who won first prize in 2015’s Nikon Small World video competition for this video of a single-celled Campanella ciliate being swallowed by a Trachelius predator. Apparently, he had scooped some pond water from a local pond, thinking he would show someone how to look through a microscope. When he leaned in and saw one protist swirling suspiciously close to its neighbor, he thought, “Eh, something’s up. I’m going to shoot this.” And he did. And he was so right.
Oh, and one last thing. Sometimes ciliates get inside their food AND GET OUT! This is Win van Egmond’s true-life video of two ciliates feasting on a baby copepod, and they both wiggle out—through a tiny hole …