Markus Varesvuo / Female Black grouse (Tetrao / Lyrurus tetrix) perched in Willow feeding, Utajarvi, Finland, May.

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.

Jussi Murtosaari / Scarce tortoiseshell butterfly (Nymphalis xanthomelas) on pussy willow, Luhanka, Keski-Finland, April. / Central Finland, Finland, April.

Guy Edwardes / 2020VISION / Pussy willow catkin (Salix caprea) bursting out from bud, Somerset Levels, Somerset, England, UK, April

Andy Sands / Mining Bee (Andrena clarkella) on Sallow catkin, Hertfordshire, England, UK, March

Andy Sands / Mining Bee (Andrena clarkella) on Sallow catkin, Hertfordshire, England, UK, March

Ross Hoddinott / Sallow / Pussy willow {Salix caprea} catkin, Cornwall. UK

Duncan Usher / Blue Tit (Cyanistes caeruleus) in Hazel (Corylus avellana) bush, Bursfelde, Lower Saxony, Germany

Duncan Usher / Blue Tit (Cyanistes caeruleus) pair on flowering Hazelnut (Corylus avellana) branch, Lower Saxony, Germany

Duncan Usher / Blue Tit (Cyanistes caeruleus) pair on flowering Hazelnut (Corylus avellana) branch, Lower Saxony, Germany

Linda Pitkin / Male flowers, catkins, of Common hazel (Corylus avellana), Surrey, England. February.

Philippe Clement / White willow (Salix alba) showing leaves and female catkins producing seeds embedded in white down, Belgium. June

Jeff Foott / Woolly Willow (Salix lanata) male catkin flowers in spring, Iceland. May.

Will Watson / Male Almond willow (Salix triandra) catkins, Withy Bed, Herefordshire, England, UK.

Will Watson / Large pollarded White willow (Salix alba) with male catkins, Yazor Brook Valley, Herefordshire, England, UK. April, 2021.

Will Watson / White willow (Salix alba) male catkins, Yazor Brook, Herefordshire, England, UK. Controlled conditions.

Will Watson / White willow (Salix alba) male catkins, Yazor Brook, Herefordshire, England,UK. Controlled conditions.

Will Watson / Basford crack willow (Salix x fragilis nothovar. basfordiana), male catkins, Kenwater, Leominster Priory, Herefordshire, England, UK. April.

Will Watson / Basford crack willow (Salix x fragilis nothovar. basfordiana), male catkins, Kenwater, Leominster Priory, Herefordshire, England, UK. April, 2021.

Will Watson / Basford crack willow (Salix x fragilis nothovar. basfordiana) developing female catkins, Bodenham Lake Nature Reserve, Herefordshire, England, UK. April.

Will Watson / Basford crack willow (Salix x fragilis nothovar basfordiana) female catkins, Bodenham Lake Nature Reserve, Herefordshire, England, UK. Controlled conditons.

Will Watson / Goat willow (Salix caprea) female catkins, Herefordshire, England, UK. Controlled conditions.

Will Watson / Goat willow (Salix caprea) male catkins / pussy willow, Herefordshire Plateau, England, UK. Controlled conditons.

Will Watson / Purple willow (Salix purpurea), male catkins, old withy bed, Herefordshire lowlands, England, UK. Controlled conditions.

Will Watson / Tall Cricket bat willows (Salix alba var. caerulea) trees with leaves and catkins, Bodenham Lake Nature Reserve, Herefordshire, England, UK. May, 2021.

Will Watson / Crack willow, (Salix x fragilis) female catkins, River Frome, Herefordshire England, UK. Controlled conditions.

Will Watson / Crack willow (Salix x fragilis) female catkin and young leaves, The Leen, Herefordshire, England, UK.

Nigel Cattlin / Male catkins of Silver birch (Betula pendula) open and mature with young leaves and female catkins developing, Berkshire, UK, March.

Nigel Cattlin / Male catkins of Silver birch (Betula pendula) open and mature with young leaves and female catkins developing, Berkshire, UK, March.

Nigel Cattlin / Male catkins of Silver birch (Betula pendula) open and mature with young leaves and female catkins developing, Berkshire, UK, March.

Nigel Cattlin / Alder (Alnus glutinosa) unopened purple tinged male catkins with smaller female catkins against a blue sky, Berkshire, UK, March.

Nigel Cattlin / Alder (Alnus glutinosa) unopened purple tinged male catkins with smaller unopened female catkins, Berkshire, UK, February.

Nigel Cattlin / Alder (Alnus glutinosa) unopened purple tinged male catkins with smaller unopened female catkins, Berkshire, UK, February.

Nigel Cattlin / Leaves and female catkins of a Silver birch tree (Betula pendula) in spring, Berkshire, England, May

Eric Baccega / European greenfinch (Chloris chloris chloris) on branch with Hazel catkins (Corylus), Moselle, France, February.

Eric Baccega / European greenfinch (Chloris chloris chloris) on branch with Hazel catkins (Corylus), Moselle, France, February.

Michel Poinsignon / Blue tit (Parus caeruleus) perched on Hazel branch with catkins, Lorraine, France, February

Jussi Murtosaari / Brimstone butterfly (Gonepteryx rhamni) male nectaring on Goat willow (Salix caprea) catkins. Jyvaskyla, Finland. May.

Adrian Davies / Pussy willow (Salix caprea) seeds blowing from catkins. Surrey, England, UK. April.

Fabrice Cahez / Catkins on Cottonwood (Populus nigra) Loire, France, April.

Paul Harcourt Davies / Downy birch (Betula pubescens) catkins. Dolomites, Italy. June.

Paul Harcourt Davies / Swiss willow (Salix helvetica) catkins.Dolomites, Italy. June.

Nick Upton / English / Pedunculate oak (Quercus robur) flowers and newly opened leaves, Wiltshire, UK, April.

Nick Upton / English / Pedunculate oak (Quercus robur) flowers and newly opened leaves, Wiltshire, UK, April.

Nick Upton / English / Pedunculate oak (Quercus robur) flowers and newly opened leaves, Wiltshire, UK, April.

Jussi Murtosaari / Honey bee (Apis mellifera) with laden pollen sacs flying towards Pussy willow (Salix caprea) catkins. Jyvaskyla, Central Finland. April.

Nigel Cattlin / Male catkins on a walnut tree (Juglans regia) with young leaves in spring, Berkshire, England, UK, May