A
mating plug, also known as a
copulation plug,
sperm plug,
vaginal plug,
sement or
sphragis, is gelatinous secretion used in the
mating of some species. It is deposited by a male into a female genital tract, such as the vagina, and later hardens into a plug or glues the tract together. While females can expel the plugs, the male’s sperm still gets a time advantage in getting to the egg, which is often the deciding factor in fertilization.