Self-insemination

Self-insemination (also known as "selfing") is a mating behavior engaged in by multiple flatworm species, such as the free-living Macrostomum hystrix,[1] and some sea slugs.

From the site of injection, sperm migrate posteriorly to the female reproductive organs (ovaries) where fertilization occurs.

There is also a reduction in the number of hatchlings produced through self-insemination and a decrease in the survival of these offspring, which suggests that this method of reproduction is costly to the parent.

[4] Therefore, members of this species avail of delayed self-insemination as a conditional reproductive strategy to endure through periods where mates are scarce.

[3] It may be beneficial for hermaphroditic species to seldom reproduce via self-insemination since they can avoid the laborious costs of reproduction to the female function as experienced through traumatic insemination ― such as in the case of the sea slug Alderia willowi.