Abstract
The earthworm ecological categories defined by Marcel Bouché between 1971 and 1977 were successful and universally adopted. However, two silent shifts can be detected about their use. The first shift is that most of the authors forgot that the three main categories (anecic, endogeic and epigeic) were indeed the three poles of a ternary plot between which all the existing species should be placed. This is the reason why, intermediate categories were used by Marcel Bouché (epi-anecic, endo-anecic and endo-epigeic and intermediate, i.e. in the centre of the ternary plot). This first shift made a categorical representation out of a continuous world and this leaded to difficulties in assigning accurately some earthworm species. The second shift is the use of ecological categories as functional groups, something Marcel Bouché never did since he never intended to describe the effects of earthworms on their environment. The consequences of these shifts are discussed. In conclusion, we recommend to (i) read the seminal papers (however written in French), (ii) use the intermediate ecological categories in order to better describe the characteristics (and their variability) of earthworm species and (iii) not use the term « functional group » for ecological categories.