Glow worms can switch on and off to a daily biological rhythm

Canberra, September 1 : An Australian researcher has found that glow worms can switch their prey-caching light on and off to a daily biological rhythm.

According to a report by ABC News, the researcher in question is Dr David Merritt of the University of Queensland, who has reported his findings in the current issue of the journal Biological Rhythms.

Glow worms are larvae of a particular type of fly that only lives in Australia and New Zealand.

Special cells in the rear end of the animal produce light that is used to attract prey.

The larvae use strings of silk, beaded with sticky drops of mucus, to snare their victims that are attracted to the light.

"It's like a spider with its web," said Merritt.

Merritt has filmed glow worms living in moist rainforests to find out when they turn on and off.

"A biological rhythm in the animal determines when they will turn on and when they will turn off," said Merritt.

"In the rainforest, the daylight causes them to switch off. They only turn on at night and turn off around dawn," he added.

Merritt confirmed this was the case in the lab and tested what happened when the glow worms were put into constant darkness.

"If they were reacting just to light, you would expect them to be glowing continuously once they go into constant darkness. But they don't. They maintain a cycle," he said. "They have this internal rhythm like we have an internal rhythm for wanting to sleep," he added.

According to Merritt, the light is important for synchronizing the switch and the longer these worms are kept out of the light the more out of sync their glowing gets.

Merritt's discovery in Queensland rainforest glow worms made him wonder whether glow worms that live in caves and never see daylight also have a synchronised circadian rhythm.

"Most people think cave animals are arrhythmic because they never see light," he said.

Merritt said that he imagined the glow worms would be glowing constantly or each would have their own individual out-of-sync light cycle.

To his surprise, when he filmed glow worms in Tasmanian caves, he found they did switch on and off in a closely synchronised way.

"They switch off when it's night time outside of the cave and they switch on when it's daylight outside of the cave," he said.

ANI