Occurrence of C. elegans and C. remanei on compost and apple samples between July 2011 and December 2012 at different sampling sites. The months for which no rotten apples were available in the Münster farming museum are marked with a cross. In Kiel, rotten apple samples could be collected during the entire sampling period. For each substrate and location, at least six and usually more than ten independent samples were assessed for the presence of Caenorhabditis nematodes. More details are in given in Table 2, and Additional file 5: Table S1 and Additional file 6: Table S2.