•Mull and Moder are two different ways of life or life “strategies”.•Agroecosystems exhibit a poorly known humus form that is neither Mull nor Moder.•Humus forms must be considered as solving the soil diversity puzzle. Most scientific papers dealing with soil biota do not describe the humus form or even mention the humus type, although it’s the habitat of micro- and macro-organisms, and the environment they contribute to create. Traditionally, and to a large extent, even today research into the topic of soil biology is rooted in agroecosystems. The humus context is neither a Mull nor a Moder but is more closely related to the former. In consequence, advance knowledge is poorly suited to the natural humus profile, notably to the Moder way of life, despite the number of studies concerning biodiversity. In this paper, Mull and Moder are taken as examples of contrasting life-styles. These two humus forms exhibit such dramatic differences that they support two different food webs enclosing high levels of unshared species diversity. A spectrum between Mull and Moder can be interpreted as a juxtaposition of hotspots coming from the two humus forms. Such an additive effect may explain much of the soil diversity enigma irrespectively of any other ecological determinants (soil, climate and vegetation).