No, in fact, most of the small, so called pest species are hermaphrodites that don't need a mate at all. But if there's more than one, they will mate, because it broadens the gene pool, and that enhances survival.
The little gel sacs can each hatch out up to a dozen or so babies, depending what species laid them. Commonly you see bladder snails, fast movers that are dark coloured and rarely get much over a quarter or 3/8 inch long, ramshorns, which have a flat spiral shape shell they carry vertically, and can be several colours, brown, red, blue, chocolate or leopard, rarely exceeding a half inch in width, and other pond snails which usually have paler colour bodies, similar conical shells to the bladder snails but paler in colour and can grow much larger, over a half inch. There is even a very tiny flat spiral shell species that never gets over a quarter inch wide, and is super thin, carrying it's shell horizontally. Kind of cute and don't breed nearly so fast as other snails do.
There are also mystery snails, giant ramshorns and asolene spixi snails, all part of the Apple snail family. Mystery snails most common, many, many colours, get up to golf ball size or a bit more. Giant apple snails get to baseball size eventually and will eat the plants. Giant ramshorns get as big as mystery snails but also have a flat spiral shell carried vertically. Spixis are striped and eat other snails of any kind, but are useful because they also eat thing like hydras.