FYFD

Tag: worms

  • The Fluidity of Worm Blobs

    The Fluidity of Worm Blobs

    The aquatic blackworm forms blobs composed of thousands of individual worms for protection against evaporation, light, and heat. The worms braid themselves together (Image 1). Once a blob forms, it is extremely viscoelastic, displaying properties both solid and fluid in nature (Image 2).

    The worm blobs act like a collective; they bunch up to prevent evaporation that would desiccate the worms. Under intense light, the blob contracts (Image 3). The worms also prefer colder temperatures (again, to prevent evaporation) and will move toward the colder side of a temperature gradient. Under dim light, they’ll move individually, but in brighter light, the worms move collectively as a blob (Image 4).

    To do so, worms on the colder side of the blob pull toward the cold, whereas worms elsewhere in the blob wiggle (Image 5). Their wiggling helps lift the blob and reduce its friction so that the pulling worms can move the blob in the right direction. For more, check out this excellent thread by one of the authors. (Image and research credit: Y. Ozkan-Aydin et al.; via S. Bhamla; submitted by Maximilian S.)

  • Studying Active Polymers Using Worms

    Studying Active Polymers Using Worms

    I’ve covered some odd studies in my time, but this might be the strangest: to understand how active polymers affect viscosity, researchers loaded drunk worms into a rheometer. Active polymers are long-chain molecules that, like worms, can move on their own using stored energy or by extracting energy from their surroundings. Their dynamics are tough to study, though, because individual polymers are almost impossible to observe while a suspension of them is being deformed.

    Enter the humble sludge worm. Often sold as fish food, these worms — like the polymers they’re meant to imitate — are individually quite wiggly but, given their size, are far easier to observe. Researchers placed them in a custom rheometer in a solution of water and observed how the worm mass responded when sheared by a spinning top plate (Image 3). Like active polymers, the worms exhibited shear-thinning; the faster the plate spun, the lower the worms’ viscosity, likely because the additional force helps align the worms.

    But how do active worms compare with passive ones? The obvious solution would be to repeat their tests with dead worms, but the researchers found a more humane method: by adding some alcohol to the water, they temporarily reduced the worms’ activity, allowing them to compare active and passive worms (Image 2). Once rinsed in water, the worms sobered up and returned to their normal activity levels.

    The researchers found that both the active and passive worms exhibited shear-thinning as the force on them increased, but the shear-thinning in the active worms was not as pronounced, presumably because the movements of individual worms prevented them from aligning smoothly. (Image and research credit: A. Deblais et al.; via Gizmodo and APS Physics)

  • Collective Motion: Worms

    Collective Motion: Worms

    Although most animals are more solid than fluid, what happens when you put many of them together can be strikingly fluidic. Above you see the black aquatic worm, Lumbriculus variegatus, which must keep moist to stay alive. An individual worm will die within an hour of being removed from the water, but, in a group, the worms can survive far longer. They do so, in part, by acting like a viscoelastic fluid, a material with both solid (elastic) and fluid (viscous) properties.

    In small groups, the worms squirm tightly together to minimize their collective surface area and prevent themselves from drying out. But in larger groups, the worm blobs begin sending out feelers, searching for more advantageous circumstances. In the top image, you can see this causes three of the blobs to ultimately merge into an even bigger one. The worm collective can also “liquify”, allowing the blob to change shape and tackle obstacles like flowing through a pipe. (Image and research credit: Y. Ozkan-Aydin et al.; via Science)

    This is the second post in our series on collective motion. Check out the first post here.