In 2025, Konstanz scientists looked very closely at rotting fruit in local orchards, and observed what no one had before—worms, hundreds of them, twisting skyward into self-assembled living structures known as "towers". It was the first time anybody had seen this mysterious behavior outside of the laboratory. Back in the lab, the team showed how these towers could attach to fruit flies, supporting a long-standing idea: towering worms may be trying to hitchhike on animals to reach new habitats. While the lab experiments confirmed that towers can latch onto potential carriers, it remained unclear which animals actually transported these worm stowaways in the wild.
Now, the team believes they have identified the carriers of the original worm towers: two sap-feeding beetles, both invasive crop pests in Europe. While the researchers did not directly observe worm towers attaching to the beetles, they surveyed several hundred invertebrates from orchard fruit and found dense clusters of the worms exclusively on these beetles. Genetic analysis revealed that the worms forming the original towers belong to a previously undescribed species, which the researchers named Caenorhabditis apta.
"It's fascinating that C. apta prefers to attach to just these two beetles, out of the dozens of invertebrate species that we examined," says first author Dr. Ryan Greenway, a research coordinator at the Max Planck Institute of Animal Behavior (MPI-AB). "Now we are looking at whether these worm clusters on beetles get there through towering, or if they can be formed after individual worms attach to the beetles instead."
Hidden partnerships
Nematodes are the most abundant animals on Earth, yet how they spread through the world remains largely unknown. Because of their tiny size, many species rely on hitchhiking—attaching to larger animals, known as vectors, to reach new habitats.
These hidden partnerships can have significant consequences. In agriculture, for example, some insect-vectored nematodes are responsible for spreading plant diseases: the pinewood nematode, carried by longhorn beetles, has destroyed forests across multiple continents.
Yet beyond a handful of economically important cases, we know almost nothing about which animals transport most nematodes in the wild. This gap limits our ability to understand how these abundant organisms move, invade new regions, and influence ecosystems.
On the trail of C. apta and its vectors
After discovering the relationship between C. apta and the beetles, the team began to wonder whether this association might extend beyond German orchards. The newly described nematode had only been recorded in European collections since 2010, while both beetle species arrived in Europe in the early 2000s, one from North America and the other from the western Pacific. This raised a possibility:
"What if C. apta hitched a ride into Europe on the wings of the beetles?" asks Greenway.
To explore this, the team compared global records of the two beetles with collections of C. apta and its closest relatives. They found overlapping distributions with one of the beetle species—the strawberry sap beetle—in North America, pointing to a possible route by which C. apta reached Europe.
Importance for agriculture and ecosystems
If C. apta is a recent arrival, its interactions with native European species could already be driving ecological and evolutionary changes, altering food webs and the processes of fruit decomposition in orchard ecosystems, the scientists say.
"The introduction of a new nematode species in Europe might not seem like a big issue," says Greenway, "but we know that nematodes can play an important role in helping their vectors spread, and vice versa." The research team is now looking to see if C. apta hitchhikers might benefit, or even hinder, their beetle vectors. "We might even find ways to use C. apta to limit the spread of these sap beetles, which has implications for managing these well-known crop pests," he says.
The study provides rare insight into the forces shaping the ecology and evolution of nematodes. "We know surprisingly little about the natural history of nematodes, despite their abundance and despite C. elegans being one of the best-studied organisms in biology," says senior author Dr Serena Ding, who leads the Genes and Behavior Group at MPI-AB. "This study shows what we can learn when we move beyond the lab and observe them in their natural habitats together with the other organisms they interact with."
