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.)