Scientists have concluded that the so-called mint sauce worm is a social animal that enjoys sunbathing with its buddies.
The worms are a kind of marine flatworm that measure just a couple of millimeters in length, which collect in groups of microorganisms on the seashore known as biofilms. They are green due to the algae that live in their bodies, writes Stephanie Pappas for LiveScience.
Sunbathing worm hangs out to make their lives better
Researchers have found that when multiple worms are put together they swim in circles, nose to tail. The team believes that in this way they can adjust the amount of sunlight that hits the algae that live inside them.
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“These worms, by being social and aggregating, can create local conditions that better suit themselves,” said study leader Nigel Franks, a biologist at the University of Bristol in the United Kingdom.
Franks found a large population of the worm on the British island of Guernsey, and started studying them. “As soon as you had them at high density,” Franks said, “they began this circular milling behavior.”
Circular milling shows appetite for social life
Nose-to-tail circular milling has also been observed in fish, some caterpillars and some insects, including ants. Milling “is normally a great indication that [animals] are responding very strongly to one another in a very social way,” Franks said. “And actually, social behavior in these worms had never been recorded before.”
To test the theory Franks observed the behavior of a group of mint-sauce worms and compared it to computer simulations of similar sized worms moving at similar speeds. The real worm group behaved much more socially than the simulation predicted, proving that the behavior was not random.
So far no one has tested why the plant-animals behave this way, but the suspicion is that it has something to do with nutrition. The worm would theoretically be better off finding a spot where their algae would work more efficiently, but they tend to choose areas that are slightly too sunny. However their sociability means that this isn’t a problem.
“If they form a biofilm — a sort of sheet of many worms in a quite dense layer — they could pop in and out of that layer to regulate the amount of sun they’re getting,” he said. Further investigations could focus on individual worms, tracking their movements between layers.