Snail Orgy

This morning I noticed that one of my Astrea snails had a pile of white things around it that resembled little sesame seeds. Looking around some more I noticed them around another snail. Then I noticed them on top of several rocks. I looked back at the first snail and I happened to see an egg shoot out of the snail. It appears to me that several of the snails in my tank decided to lay eggs on the same night. Yesterday was the first day of spring. Are snails smarter than we think? Can they read the calendar? How do they know to spawn at the same time with no additional cues?
In the picture above you can see the pile of eggs lying below the snail. The vent from which the eggs were laid is also visible just below the shell and just to the left of the egg pile. If all goes well I may be overrun with snails soon.