The short answer
Yes — mystery snails need both a male and a female to breed. Unlike self-fertile pest snails, they can’t reproduce alone, so a single mystery snail will never multiply. When you do have a pair, the female lays a distinctive pink egg clutch above the waterline, and the young hatch out from there. That makes their breeding easy to both encourage and prevent, depending on what you want.
How mystery snail breeding works
Mystery snails have separate sexes, and a male must fertilise a female for eggs to be viable. After mating, the female crawls above the water surface — onto the glass, the lid or the rim — and deposits a cluster of eggs in a firm pink or orange clutch. She lays out of the water because the eggs would drown if submerged, which is also why the tank needs an air gap between the water and the lid.
Encouraging or preventing babies
If you want young, keep a small group (around five) to be sure of having both sexes, feed well, and leave the clutches in place until they hatch in two to four weeks. If you don’t want babies, either keep a single snail or simply scrape each pink clutch off before it hatches — easy, since it sits in plain view above the water.
Compared with nerites
This is the opposite of nerite snails, whose eggs never hatch in freshwater at all — see do nerite snails reproduce. Learn more on the mystery snail care page, and pair them with a good filter and steady water you confirm with a test kit.