Isopods begin life as tiny free-swimming males and have the ability to transform into females. They attach to a fish in the region of the head with several pairs of hook-like legs. From then, they lose their ability to swim and remain where they settle for life. When a male attaches itself to the host with a female already in place, it mates with the larger female. When the female dies, the male changes sex and awaits the arrival of a young male.