Sven Zacek / Eurasian beaver (Castor fiber) with Willow (Salix sp) branch for winter stockpile. Near Suur Emajogi River, Tartumaa, Southern Estonia. January.

Michael Quinton / Snowshoe Hare (Lepus americanus) browsing on a Pussy Willow (Salix discolor) twig in winter, Alaska

Michael Quinton / Snowshoe Hare (Lepus americanus) browsing on a Pussy Willow (Salix discolor) twig in winter, Alaska

Michael Quinton / Snowshoe Hare (Lepus americanus) browsing on a Pussy Willow (Salix discolor) twig in winter, Alaska

Solvin Zankl / Honey bee (Apis mellifera) collecting pollen on Goat willow (Salix caprea) Kiel, Germany, April.

Nick Upton / Female Eurasian beaver (Castor fiber) and five kits feeding on a Willow (Salix) sapling, River Otter, Devon, England, UK, July. Part of Devon Wildlife Trust's Devon Beaver Trial.

Andres M. Dominguez / Bacteria (Lepthotryx discophora) causing iridescent patterns and White willow tree leaf (Salix alba) in river, Sierra de Grazalema Natural Park, southern Spain, November.

Sven Zacek / Misty lake, with trees reflected in the water, and Willow (Salix) trees silhouetted on the shore, Suur Emajogi river, Tartumaa, Estonia, May 2014.

Alex Hyde / Peacock butterfly (Inachis io) feeding on Goat Willow catkins (Salix caprea), an important food source for pollinators in early spring. Peak District National Park, UK. April.

Nick Upton / Eurasian beaver (Castor fiber) gnawing the trunk of a Willow tree (Salix sp.) in woodland enclosure at night. Devon Beaver Project, run by Devon Wildlife Trust, Devon, UK, April. Taken by a remote cam...

David Tipling / 2020VISION / Nightingale (Luscina megarhynchos) singing in willow (Salix sp), Norfolk, England, UK, May.

Ammonite / Close-up of a Buff-tailed bumble bee (Bombus terrestris) feeding from Willow (Salix) catkins, before flying out of frame, France, March.