Simon Colmer / Honeybee workers exchanging food - known as trophallaxis (Apis mellifera) Sussex, UK

Simon Colmer / Honey bee (Apis mellifera) workers exchanging food - known as trophallaxis, Sussex, UK

Piotr Naskrecki / Two slugs exchanging fluids, Atewa Range, Ghana

Bruno D'Amicis / Goshawk (Accipiter gentilis) female and male exchanging prey at plucking site in old-growth Beech (Fagus sylvatica) forest, . Abruzzo, Lazio and Molise National Park / Parco Nazionale d'Abruzzo, L...

Bruno D'Amicis / Goshawk (Accipiter gentilis) female and male exchanging prey at plucking site in old-growth Beech (Fagus sylvatica) forest, Abruzzo, Lazio and Molise National Park / Parco Nazionale d'Abruzzo, Laz...

Konrad Wothe / Pair of Black woodpeckers (Dryocopus martius) exchanging incubation duties at nest, Bavaria, Germany, April.

Tui De Roy / Swallow-tailed Gull (Creagrus furcatus) pair exchanging food, Genovesa Island, Galapagos Islands, Ecuador

Paul Bertner / Green Tree Ant (Oecophylla smaragdina) pair exchanging food, Cat Tien National Park, Vietnam

Paul Bertner / Green Tree Ant (Oecophylla smaragdina) pair exchanging food harvested from treehopper, Angkor Wat, Cambodia

Paul Bertner / Green Tree Ant (Oecophylla smaragdina) pair exchanging food, Angkor Wat, Cambodia

Paul Bertner / Green Tree Ant (Oecophylla smaragdina) pair exchanging food, Angkor Wat, Cambodia

Paul Bertner / Green Tree Ant (Oecophylla smaragdina) pair exchanging food, Angkor Wat, Cambodia

Paul Bertner / Spiny Ant (Polyrhachis sp) pair exchanging food, Danum Valley Conservation Area, Sabah, Borneo, Malaysia

Dave Bevan / Pair of Wood pigeons (Columba palumbus) perched in a Hawthorn tree (Crataegus monogyna), exchanging food, Gloucestershire, England, UK, June.

Frederique Olivier / Wide angle view of a pair of Royal penguins (Eudyptes schlegeli) exchanging an egg in a colony, Macquarie Island, Australian Antarctica.

Mark Taylor / Collie cross dogs Brec and Bliss, exchanging angry snarls. Brec with hackles raised.

Ingo Arndt / Whiskered Tern (Chlidonias hybrida) male passing mayfly to female during courtship, Danube Delta, Romania

Thomas Hinsche / Common Kingfisher (Alcedo atthis) pair exchanging fish during courtship, Saxony-Anhalt, Germany

John Cancalosi / Leopard slug (Limax maximus) pair mating, white male organs exchanging sperm, hermaphroditic species, New York, USA, August.

David Pattyn / Great Crested grebes (Podiceps cristatus) performing courtship dance and exchanging weed as part of ritual, La Dombes area, France, June

Simon Colmer / Honey bee (Apis mellifera) workers exchanging food - known as trophallaxis, Sussex, UK

Donald M. Jones / Limpkin (Aramus guarauna) pair exchanging snail, central Florida

Tui De Roy / Rockhopper Penguin (Eudyptes chrysocome) pair exchanging incubation duties, New Island, Falkland Islands

Heike Odermatt / Northern Gannet (Morus bassanus) pair exchanging nest material mid-flight, Helgoland, Germany

Scott Leslie / Tree Swallow (Tachycineta bicolor) pair exchanging food on the fly, Tobeatic Wilderness Area, Nova Scotia, Canada

Heidi & Hans-Juergen Koch / Honey Bee (Apis mellifera) pair right before exchanging food mouth to mouth, Bee Station at the Bavarian Julius-Maximilians-University of Wurzburg, Germany

Heidi & Hans-Juergen Koch / Honey Bee (Apis mellifera) pair exchanging food mouth to mouth, Bee Station at the Bavarian Julius-Maximilians-University of Wurzburg, Germany

Heidi & Hans-Juergen Koch / Honey Bee (Apis mellifera) pair exchanging food mouth to mouth, Bee Station at the Bavarian Julius-Maximilians-University of Wurzburg, Germany

PREMAPHOTOS / Edible snails courtship / mating (Helix pomatia) UK. In the mating season, all snails are male, exchanging sperm by hypodermic insertion of "love darts". Later on, the snails become female and fertili...

Tui De Roy / Flightless Cormorant (Phalacrocorax harrisi) endemic courting pair snake-necking and exchanging nest-building gifts, Punta Espinosa, Fernandina Island, Galapagos Islands, Ecuador

Tui De Roy / Flightless Cormorant (Phalacrocorax harrisi) endemic courting pair snake-necking and exchanging nest-building gifts, Punta Espinosa, Fernandina Island, Galapagos Islands, Ecuador

Tui De Roy / Laysan Albatross (Phoebastria immutabilis) parents exchanging chick guarding duties, Midway Atoll, Hawaii

Tui De Roy / Laysan Albatross (Phoebastria immutabilis) parents exchanging chick guarding duties, Midway Atoll, Hawaii

Bruno de Faveri/ BIA / Arctic Tern (Sterna paradisaea) pair exchanging food, Farne Islands, England, United Kingdom

Sergey Gorshkov / Snowy Owl (Nyctea scandiaca) trio exchanging food in flight, Wrangel Island, Russia

Marie Read / Northern harrier (Circus cyaneus) pair exchanging food in courtship while flying near nest, Montezuma National Wildlife Refuge, New York, USA.

Brian Bevan / Great crested grebe (Podiceps cristatus) pair exchanging incubation duties at nest, Bedfordshire, UK, April.

Ingo Arndt / Honey bees (Apis mellifera), workers exchanging food on honeycomb, Germany

Ingo Arndt / Honey bees (Apis mellifera), workers exchanging food on honeycomb, Germany