The term 'They Fly By Night' refers to four different species of nocturnal animals: moths, OWLS, BATS, and redeyes. Moths are small insects with wings that come in a variety of colors and patterns. OWLS are birds of prey that have large eyes and a distinctive call. BATS are small mammals with wings that use echolocation to navigate in the dark. Redeyes are a type of fly that are active at night and have bright red eyes. All four of these species fly by night, hence the term.