A wide variety of animals have names describing them as black-legged.
Birds:
Black-legged kittiwake
Black-legged seriema
Black-legged dacnis
Amphibians:
Black-legged dart frog
Invertebrates:
Arthropods
Insects
Blacklegged tick, Ixodes scapularis
Black-legged water-snipefly, Ibisia marginata
Black-legged horsefly, Hybomitra micans
Violet black-legged robberfly, Dioctria atricapilla
Blackleg tortoiseshell, another name for the large tortoiseshell butterfly