As soon as the Willow catkins start producing pollen, the trees become a valuable food source for insects of all kinds.
This queen Bombus terrestris is stocking up before she retires to her nest:

And a number of flies were also feeding, including this Lesser Dungfly:
The Twin-Spotted Quaker moth - Orthosia munda - is also a Willow pollen feeder, which is why it is only seen in March and April:
Another new moth came to light last night: the Red Chestnut - Cerastis rubricosa. The various Chestnut species can be very tricky to separate, especially in the cusps when their flying dates overlap, but the reddish colour, combined with the wing shape and the grey flashes at the edge of the wing make this look fine for that species: