Staminate catkin
fully out.
The staminate flowers grow on one willow tree, and the pistillate ones on another.
The pollen in the staminate flowers is very abundant and is carried by the wind or by insects to the pistillate flowers. If you shake a twig of ripe staminate catkins, your hands and clothes will be covered with pollen dust.
Pistillate
catkin.
Bees are fond of willow pollen and eagerly gather it in the early spring. The willow catkin has a tiny drop of nectar at the base of each little flower, and bees and flies are fond of this and visit the willows to get it. Of course, as the insects fly from one catkin to another, they carry pollen from one to another.
After a time the staminate flowers wither and fall, but the pistillate ones are followed by seed pods, and the stem that bears them lengthens to make room for the growing pods, and at last when the seeds are ripe the pods split open and out come the tiniest of little seeds, each with a tiny plume of down, and away they fly.
There are a great many species of willow, and not all of them are as pretty as the pussy willow. One reason why the pussy willow is so pretty is that the catkins appear before the leaves. In some willows the catkins come with the leaves, and in some they come after the leaves are fully grown. Many willows have bright red or yellow or green stems that give color to the landscape even in midwinter.