Why do deep-sea anglerfish have glowing lures?

Deep-sea anglerfish use a glowing appendage called an esca as a lure to attract prey in near-total darkness. In many species, the light is produced by symbiotic bioluminescent bacteria living inside the lure, rather than by the fish itself. This adaptation is useful in the deep ocean, where food is scarce and visibility is extremely limited. The female anglerfish is usually much larger than the male, and some males live as tiny parasites attached to females. The lure helps the fish conserve energy by bringing food close enough to strike quickly.