Paul Hobson / Grass snake (Natrix natrix) swimming amongst duck weed, Oxfordshire, UK

Barry Mansell / American alligator (Alligator mississippiensis) in duck weed filled pond, Everglades National Park, South Florida, USA, August.

Roger Powell / Pintail (Anas acuta) drake, feeding on weed on the sea. Varanger shore, Finmark, Norway, June.

John Cancalosi / Green Frog (Rana clamitans) among duck weed on water surface. New York state, USA, September.

Loic Poidevin / Female Mallard Duck (Anas platyrhynchos) on water among flowering pond weed. The Vendeen Marsh, French Atlantic Coast, April.

Fabio Liverani / Wolf spider (Pardosa wagleri) carrying young on its back over water on duck weed, Lake Cernika, Slovenia

Fabio Liverani / Wolf spider (Pardosa wagleri) carrying young on its back over water on duck weed, Lake Cernika, Slovenia

Tom Vezo / American alligator in duck weed {Alligator mississippiensis} Texas, USA

Michael W. Richards / Mallard (Anas platyrhynchos) ducklings preening and feeding on duckweed in pond, Somerset, UK, July.

Nick Upton / Two Gadwall (Anas strepera) females dabbling for pond weed in a marshland pool, Catcott Lows National Nature Reserve, Somerset, UK, September.