Myrmecoleón
Also known as Formicaleon, Formicaleun, and Mirimicioleon, this is a hybrid beast, half ant, half lion.
Among its many variants, the one cited in medieval bestiaries portrays it as a creature with the head of a lion and the body of an ant, the offspring of a cross between both species. Each part retains its own nature.
The myrmecoleón dies of starvation because the leonine part feeds on meat, while the ant part can only digest grain.