Megacrania tsudai adan (Phasmatidae) is an endemic subspecies of stick insect on the Sakishima Islands of the Ryukyu Archipelago that feeds on the leaves of the screw pine. This species can reproduce by parthenogenesis and it is believed to spread their distribution by seawater dispersal of eggs. This study examined the effect of seawater floating on hatching rate and egg period of this species, and discusses adaptation to seawater dispersal. Under control conditions (NC), eggs were put on wet cotton. In seawater treatments, four floating periods were examined: 1) 30 days (MC 30); 2) 60 days (MC 60); 3) 90 days (MC 90); and 4) floating for duration of the experiment (M; = 365 days). Hatching rate of NC was 74.0% and the egg period was 124.6±13.4 days. No significant differences were found in hatching rates among the five treatments. Egg period was significantly different between NC, three MCs and M. The egg period of M was the longest and of NC the shortest. These results show that floating length does not affect egg period. As hatching rate was constant regardless of floating period, and the M egg period was significantly the longest, we theorize that eggs of M. tsudai adan are adapted to seawater dispersal.