Dependency chains

Willow catkins have started to appear on a few trees, so the dependent species will be stirring from their winter hiding places: the larvae of some micromoths live inside the catkins, causing them to drop early; larger moths of the Xanthia family feed on the pollen; and the solitary bee Andrena clarkella gathers the pollen to feed her larvae in the underground burrow. 

Catkins of Salix

As soon as the leaves appear, a completely new set of micromoths and beetles will appear to eat the leaves or make mines inside them. This pattern of a series of dependent species will repeat itself when other trees such as Birch, Oak, Beech and Alder produce their flowers and leaves, but the Willow is the first of our trees to produce these food sources, so it's always the one to kick things off for the new season.

Willow catkins

I don't usually try to identify Willows to a single species because they hybridise and back cross very freely. This one seems most like Goat (Pussy) Willow, but I suspect there's a bit of Grey in there, too. ( I know of a lovely specimen of Dwarf x Eared Willow growing in the middle of an abandoned path: the tree produces catkins, so it's mature, but it is no more than 10 cm. tall. I'll show some pictures in June, when it's in flower.)