Watching nematodes swim the channel

For microbes, it’s not always open-water swimming. Sperm negotiate narrow reproductive tracts, infectious bacteria navigate thin layers of mucus, and many other microbes live life confined to thin biofilms. Now researchers led by Kari Dalnoki–Veress (McMaster University, Hamilton, Ontario, Canada) have devised a way to probe how confinement affects a microswimmer’s stroke. The researchers capture undulating nematodes by the tail, one at a time, with a cantilevered micropipette. The forces the roundworms generate as they wriggle can then be determined with subnanonewton precision by measuring tiny deflections of the pipette. In one setup, the tethered worms swim near a glass plate; in another, they swim in the narrow channel between two plates. In both cases, the undulating motion lies in the plane parallel to the plates—that way, although the boundaries increase the viscous resistance that a worm feels, they don’t constrict its range of motion. In the experiments, the nematodes...