Instructions
Observe a pair of mating snails. The snail on the top is male, the one on the bottom, female.
Take your snail out of the water and hold it with the opening facing up. Wait for the snail to emerge. Examine the snail's right mantle cavity for the presence of male genitalia. It will be near the edge of the shell. If the genitalia are absent, the snail is female. The Apple Snail website (see Resources) has photos showing the differences between male and female snails.
Compare the sizes and openings of multiple snails. Females are larger, with a straighter shell opening; the male has an extended "lip" around its opening.
How to Tell Between Male and Female Mystery Snails
Mystery snails, also called apple snails, are common aquatic snails often found in home aquariums. Unlike many snails, mystery snails are not hermaphrodites, although some species of mystery snail may change from female to male and vice versa. It's easiest to determine snail gender when snails are actually mating or laying eggs, but you can examine a snail at any time to determine its gender.