A reader wrote to us recently about a group of worms that he observed moving together – that is, the worms were seen crawling “as one,” such that the worms appeared to be traveling “one over the other to get to their destination.” The reader further observed that the worms were relatively small, and that the group consisted of about 50 worms. What type of worms move together, and further, why do worms crawl together as a group anyhow?

This is an interesting topic, not least because recent studies have spoken directly to the topic of worms traveling together in groups. Researchers at the University of Liege observed that annelids (a.k.a. “ringed worms,” not to be confused with the ailment ringworm), that large phylum of segmented worms that includes earthworms, work together when they are traveling. In the study, several worms were placed in a chamber, and rather than each exiting the chamber at random, the worms appeared to move together as a group.

Further, the researchers conjectured that worms work together based on their sense of touch, not on any sort of chemical trail that they leave behind. They base this hypothesis on the fact that after one worm navigated its way to food, subsequent worms did not follow the first worm’s path to the food. Since the worms didn’t follow the route of their predecessors, it is believed that the first worm didn’t leave any sort of chemical trail behind it that other worms could track. However, when two worms are placed in a maze together, they tend to navigate the maze together, suggesting that the worms were following each other based on touch. In a sense, worms make collective decisions with respect to their movements, and these collective decisions are arrived at through worms touching each other (presumably because some primitive signal is communicated this way). Worms travel in “herds,” which is basically what our reader described.

The new research also sheds light on the phenomenon of worms clumping together, which is often seen in compost bins. The traditional thought was that worms were joining together as a defense against predation or to avoid freezing. Perhaps this is true, but the worms may also be joining together for the sake of communication – to plan their next trip, as it were.

As we mentioned earlier, the study focused on annelids, and because the reader wasn’t particularly detailed in his description of the worms he saw, it’s hard to say whether this study speaks to the group movement of the worms he saw. However, even if our reader isn’t dealing with annelids, perhaps the strange movement he observed is nevertheless caused by worms communicating by touch.