Interindividual differences (bold and shy strategies) in neophobia may explain the invasive success of the worm Eisenia fetida

When they are confronted to novel environments individuals may express different kinds of behaviors. They can move a little or even stay immobile with few exploration of the new environment or they can increase their activity, move a lot and explore actively the new place. Several studies on neophobia have been conducted on vertebrate species and they distinguish bold and shy patterns in animals reactions. Less studies have been conducted on invertebrates in this area. Here I present the case of the worm Eisenia fetida that I tested in open field tests in order to detect if they present different response profiles when confronted to a novel environment and how these profiles can vary depending on size factor. I was able to distinguish two profiles, a shy/philopatric reaction present in young and adults and a bold/explorer reaction that can be observed in mature worms. From the 311 worms tested one half was bold/explorer and the other half was shy/philopatric. The existence of these two profiles may explain the invasiveness of the species: some indivivuals stay and occupy the known environments and some individuals enhance their activity in order to colonize other environments.