Damselfly nymph cases

During this hot spell I have noticed that several species of damselfly are now appearing around our garden pond.  On close inspection I noticed at least 10 damselfly nymph cases stuck to the waterlily pads where they had obviously emerged from the bottom of the pond where they had lived out their nymphal stage to hatch into the beautiful adults that I now see in all their glory.  I have never noticed this before and I think I just happened to catch them on the day they had all emerged at once.  Just shows what a bit of warm sun will do.