Matthew Maran / European robin (Erithacus rubecula) Hampstead Heath, London, England, UK. January.

Paul Williams / Giant otter (Pteronura brasiliensis) intimidates Yacare caiman (Caiman yacare) who is intruding on the otters territory, specifically latrine, Pantanal, Pocone, Brazil

Mark Moffett / Amazon Ant (Polyergus sp) female worker positioning mandibles to pierce the head of an ant from an alien nest, Sagehen Creek, California

Roger Powell / Fulmar {Fulmarus glacialis} calling aggressively to drive off intruding rival flying overhead, Caithness, Scotland, UK

Mark Moffett / Marauder Ant (Pheidologeton diversus), minor worker trail guards facing aggressive Army Ants (Leptogenys sp), Borneo

Mark Moffett / Ant (Paratrechina sp) group attacking intruder

Anup Shah / Nile crocodile {Crocodylus niloticus} (large male named Bwana Kiba) on banks of Grumeti river catches an intruding crocodile by its tail, Serengeti NP, Tanzania

GEORGETTE DOUWMA / Giant cuttlefish (Sepia apama), large battle scarred male preventing an intruding male from approaching an egg-laying female, who has now been joined by a third male. Spencer Gulf, Wayalla, South Aust...

Anup Shah / Nile Crocodile {Crocodylus Niloticus} with tail of intruding Crocodile in mouth, Grumeti River, Serengeti, Tanzania

Anup Shah / Nile Crocodile {Crocodylus Niloticus} with tail of intruding Crocodile in mouth, Grumeti River, Serengeti, Tanzania.

Yva Momatiuk & John Eastcott / Mustang (Equus caballus) stallion confronts intruder, winter, Wyoming

Yva Momatiuk & John Eastcott / Mustang (Equus caballus) stallion charging to chase away intruder in summer, Montana

Mark Moffett / Blackbellied Clerid (Enoclerus lecontei) acting as a parasite, moves into Piper Plant, replacing the Ants (Pheidole bicornis) and providing no protection for the plant

Mark Moffett / Marauder Ant (Pheidologeton diversus) pair defending the trunk trail from intruding Army Ant (Leptogenys sp) pair, India

Mark Moffett / Ant (Azteca sp) patrol on their host tree (Cecropia sp) killing intruder ant species, Costa Rica

Mark Moffett / Silverfish living in Acacia thorns with Acacia Ants

Mark Moffett / Marauder Ant (Pheidologeton diversus), major worker killing an intruder who tried to get through the trunk trail, Malaysia

Premaphotos / Common yellow dung fly (Scathophaga stercoraria). An intruding male trying to unseat a male that is already mating on dung, UK

Mark Moffett / Checkered Beetle (Cleridae) moves into Piper plant, replacing the ants and providing no protection for the plant

Michio Hoshino / Polar Bear (Ursus maritimus) mother chasing intruding bear away from her cubs, Churchill, Manitoba, Canada