Mitsuaki Iwago / Eastern Grey Kangaroo (Macropus giganteus) males fighting, Australia

Konrad Wothe / Southern Elephant Seal (Mirounga leonina) two males fighting for dominance, Macquarie Island, Australia

Konrad Wothe / Southern Elephant Seal (Mirounga leonina) males fighting for dominance, Macquarie Island, Australia

Matthias Breiter / Saltwater Crocodile (Crocodylus porosus) with mouth open, in mud, Kakadu National Park, Australia

Mark Moffett / Goat Fly (Phytalmia mouldsi) male flies eye to eye as they guard females using oviposters to deposit fertilized eggs, Queensland, Australia

Mitsuaki Iwago / Red Kangaroo (Macropus rufus) fighting males among eucalyptus trees, Australia

Mark Moffett / Jumping Spider (Bavia aericeps) two females fighting, Australia

Mark Moffett / Jumping Spider (Bavia aericeps) two females fighting, Australia

Mark Moffett / Jumping Spider (Simaetha sp) hunts and kills Australian social spiders and flies in web nest, Australia

Mark Moffett / Jumping Spider (Portia fimbriata) females fighting over eggs and nest, such battles often result in maiming or death, Queensland, Australia