And what do some mosses use as a mobile home? Millipedes! In a paper published in December 2011, S. Daniela Martínez T. et al. describe this relationship between 10 species of mosses and a tropical millipede, Psammodesmus bryophorus.
Obviously this millipede is at the cutting edge of fashion.
Field work for this study was done at the Reserva Natural Río Nambi in Colombia. As the scientists sorted the 124 millipedes they collected, they noticed that some of their P. bryophorus specimens looked a bit green...because they had moss growing on their backs. (Sadly, the paper doesn't indicate whether or not the mosses caused any uncomfortable itching.)
Intrigued, they set to work and checked the 20 P. bryophorus millipedes they collected and found that 15 of them had mossy backs. One enterprising male was conducting a party train--he had 55 individual moss plants on his back. For a closer look at how the mosses grow, check out the next photo.
Figure 2 from S. Daniela Martínez T. et al. 2011.
The authors provide a guess as to why the mosses choose this species as land to build upon: it provides a stable surface. Better to build your house on a rock than decomposing leaf litter, eh? The mosses may provide an advantage for the millipede as well: P. bryophorus has a few racing stripes down its back, and the mosses cover those up, providing camouflage. These working hypotheses will have to be tested further, of course, but they're plausible.
A final fun fact? Spores from these mosses can fall off the millipede and grow into new plants elsewhere. Imagine that, a millipede imitating Johnny Appleseed. Maybe it should be named Mildred Mossspore.
I recommend reading the article itself for more information. You can view/download it for free here.
Martínez-Torres SD, Flórez Daza ÁE, Linares-Castillo EL. (2011). Meeting between kingdoms: discovery of a close association between Diplopoda and Bryophyta in a transitional Andean-Pacifc forest in Colombia. In: Mesibov R, Short M (Eds) Proceedings of the 15th International Congress of Myriapodology, 18–22 July 2011, Brisbane, Australia. International Journal of Myriapodology 6: 29–36. doi: 10.3897/ijm.6.2187