John Abbott / Maple callus borer (Synanthedon acerni) flying, Oneida County, Wisconsin, USA. Controlled conditions. June

Franco Banfi / Southern right whale (Eubalaena australis) with callus covered in parasitic crustaceans named cyamids or whale lice (Cyamus ovalis) above eye. Golfo Nuevo, Peninsula Valdes, UNESCO Natural World Heri...

Franco Banfi / Southern right whale (Eubalaena australis) with calluses covered in parasitic crustaceans named cyamids or whale lice (Cyamus ovalis). Golfo Nuevo, Peninsula Valdes, UNESCO Natural World Heritage Site...

Richard Du Toit / Burchell's Zebra (Equus burchellii) forleg callus, Rietvlei Nature Reserve, South Africa

Mike Read / Beech tree (Fagus sylvatica) with large callus on trunk, Vinney Ridge, New Forest National Park, Hampshire, UK, September 2010

Joel Sartore / Photo Ark / Maple callus borer (Synanthedon acerni) profile, Deerwood, Minnesota. Controlled conditions.