Worms Caught Building Flesh Towers in the Wild

Scientists have just discovered something most of us probably would’ve been fine never knowing: wild nematodes—also known as roundworms—love to climb on top of each other to build fleshy, writhing towers.

Researchers in Germany detailed their discovery in a new study published Thursday in Current Biology. They found and videotaped several nematode species, living out in the wild, organizing into these living worm towers—a phenomenon previously only seen in the lab. The findings also show that the microscopic worms use these structures to climb onto animals or objects that can bring them elsewhere, though there remain many other questions about the practice.

According to senior study author Serena Ding, a researcher at the Max Planck Institute of Animal Behavior, the towers are hardly a secret among the worm science community. But the behavior had reached a sort of mythical status, since no one had ever documented it in wild nematodes. That could have meant the worms are only compelled to build towers under lab conditions, which might have limited the usefulness of any research on the behavior.

“It’s just something that always bugged me. I mean, yes, we’re studying nematode collective behavior in the tower context and other contexts, but is it real?” Ding, the leader of a lab focused on nematode research at Max Planck, told Gizmodo. “So when I started my research program four years ago, I really dedicated a push towards just actually finding nematodes at a high density and high numbers doing this stuff out there. And then we were successful.”

It ultimately took months for Ding’s colleagues, particularly co-author Ryan Greenway, to find and record instances of natural worm tower building in the decaying fruits strewn across the orchards near the University of Konstanz (one of three locations where the Institute is based). Once the towers were found, the researchers brought some into the lab for further study. They also encouraged and studied the creation of worm towers in the lab with Caenorhabditis elegans, a species frequently used for research.

“There’s the important finding of, ‘Yes, they do exist.’ But the second finding is that we actually confirm the towers can serve to disperse individuals at the same time,” Ding said. “This [has] always been thought of as a dispersal behavior, but nobody’s really confirmed it.”

The researchers observed the worms in these towers latching onto animals like fruit flies passing them by, for instance, or using them as a sort of bridge to cross otherwise unreachable gaps. Moreover, the towers appeared to collectively respond to stimuli like being touched. The fruits contained loads of nematodes, but the towers themselves were always made of only one species at a time. All of this suggests that these living buildings should be seen as temporary “superorganisms,” similar to slime molds or certain ants.

Though Ding and her team did hope and expect to find the worm towers in nature, they were surprised in other ways.

The researchers found no evidence of the lab worms taking on different roles inside the tower, for one. The worms were equally mobile, and none appeared to have an advantage over others in becoming the head of the tower (i.e. the part that most benefits from this behavior). These worms are clonal, however, meaning they’re practically identical to each other genetically. And it’s possible that things aren’t quite so chummy among more distantly-related worms in the wild.

“These are active directions which we’re trying to follow up on right now, because not everybody gets to disperse. So who gets to disperse? Are they helping each other? Are they cheating?” Ding said.

There are other questions left to be answered about these towers. The team’s lab experiments showed that C. elegans worms were capable of building towers throughout their lives, for instance, including adulthood. Previous research had suggested this behavior was only performed by dauer worms—a larval stage of life some worms adopt to survive harsher environments. At the same time, the natural towers they found were only made out of dauer worms, so maybe there’s something else that makes the behavior more common during that stage of life.

This research is only the start for Ding and her team, since they plan to pursue these mysteries further. But Ding hopes her team’s work can already impart a valuable lesson, especially to other worm researchers. She notes worms like C. elegans are commonly altered in the lab so scientists can track how certain behaviors might work on the molecular level. But she argues that there’s also still plenty more to be learned from studying them out in the real world.

“What I’m trying to do is to take really well-known organisms but study them from a more natural perspective. I want to understand not just how the behavior is generated, but also what the behavior means for the animal from a more ecological and evolutionarily relevant perspective,” she said. “At least for me, this is an important study where as a worm person, I can publish a study without using a single mutant and we’re just looking at the behavior, and what those behaviors say. For me, that’s super exciting.”

Personally, I’m just glad I now have more frightening trivia to bring up at my next party.