Nick Upton / Two Common swift eggs (Apus apus) in a nest box in a church belfry, inspected during a ringing study, Worlington, Suffolk, UK, July.

Andy Sands / Parasitic fly (Cacoxenus indigator) laying eggs into nest of Red mason bee (Osmia bicornis) in garden bee hotel / insect box . Hertfordshire, England, UK, May

Andy Sands / Parasitic fly (Cacoxenus indigator) laying eggs into nest of Red mason bee (Osmia bicornis) in garden bee hotel / insect box Hertfordshire, England, UK, May

David Tipling / Eurasian pygmy owl (Glaucidium passerinum) eggs inside nest box, Finland, April.

Lynn M Stone / Piglet in antique wooden egg box, Findlay, Ohio, USA.

LYNN M. STONE / Buff Wyandotte rooster perched on antique wooden egg case in grass beside rose bush. Calamus, Iowa, USA.

Kim Taylor / Red mason bee (Osmia rufa) female laying egg on pollen / nectar mix in egg cell of artificial bee nesting box, Surrey, UK, April

Kim Taylor / Red mason bee (Osmia rufa) female building pollen retaining wall of mud and sand to separate egg cells in artificial nest box, Surrey, UK, April

LYNN M. STONE / Portrait of Black Labrador Retriever puppy in antique wooden egg box, Illinois, USA

LYNN M. STONE / Portrait of Black Labrador Retriever puppy in antique wooden egg box, Illinois, USA

GEORGETTE DOUWMA / Newly laid chicken egg with feather in egg box, UK

Chris Newbert / Box Crab (Calappa sp) female with eggs, Papua New Guinea