Pseudoscorpions are predators of arthropods and primarily inhabit soil litter and tree bark in forests, although some species have been collected from animal nests, suggesting close associations with mammals and birds. We made preliminary observations on the life cycle and life history traits of Megachernes ryugadensis Morikawa, 1954, phoretic on the wood mice Apodemus speciosus and A. argenteus, by sampling wild specimens in the field and rearing these specimens in a laboratory. The main phoretic host at the study site was A. speciosus; we observed an average of 1–1.7 pseudoscorpions on 5–36% of mice within the 2-year study period. The observed phoretic stages of M. ryugadensis were adults and tritonymphs; the phoretic ratio on A. speciosus was relatively stable for 2 years. The duration of full development from egg to adult in M. ryugadensis was unclear, probably due to unsuitable rearing conditions; however, individuals survived as adults for over one year. Typical maternal care was confirmed in pseudoscorpions and egg hatching was synchronized to within ca. 8 h. Further study, including close examination of mouse nests, is required to elucidate the symbiotic relationship between the pseudoscorpion and host rodents.