Behaviour
A variety of different gastropod shells are used by C. erythropus, the most frequent being Littorina striata, Mitra, Nassarius incrassatus and Stramonita haemastoma, which collectively account for 85% of all the individuals studied in the Azores; in the Mediterranean, shells of Cerithium, Alvania montagui and Pisania maculosa are most used by C. erythropus.
Like other hermit crabs, C. erythropus feeds on "organic debris, decayed and fresh macro-algae with associated fauna and epiphytic algal flora, small invertebrates, and macroscopic pieces of dead and live animal tissues". It has been shown that C. erythropus individuals select substrates where they can cover large distances, and that globose shells allow them greater mobility than elongate ones.