Wednesday, April 21, 2010

Earthworm collectives

Earthworms make 'group decisions'
BBC Earth News: Earthworms form herds and make 'group decisions,' scientists have discovered. The earthworms use touch to communicate and influence each other's behaviour, according to research published in the journal Ethology. By doing so the worms collectively decide to travel in the same direction as part of a single herd...

'Our results modify the current view that earthworms are animals lacking in social behaviour,' says Ms Lara Zirbes, a PhD student at the University of Liege in Gembloux in Belgium. 'We can consider the earthworm behaviour as equivalent to a herd or swarm.'... [Description of experiments here.]

'I have observed contact between two earthworms. Sometimes they just cross their bodies and sometimes they maximize contact. Out of soil, earthworms can form balls.'... 'To our knowledge this is the first example of collective orientation in animals based on contact between followers,' the researchers wrote in the journal. 'It is also the first one of collective movements of annelids.'...

The researchers... now hope to investigate why the animals come together to form herds. One reason may be that clustering helps the worms protect themselves. Individual Eisenia fetida earthworms secrete proteins and fluids which have antibacterial properties, potentially deterring soil pathogens. They also secrete a yellow fluid to deter predatory flatworms. Gathering into groups may increase the amount of fluids covering the earthworms and hence better protect individuals.
Image source here.