Organisms use living light to solve crucial evolutionary problems. The first is attracting prey. The famous deep-sea anglerfish uses a glowing rod (illicium) filled with bioluminescent symbiotic bacteria to lure prey directly into its mouth. The second is camouflage. Some squid and fish employ a method called counterillumination: they emit light from the underside of their abdomen, the intensity of which matches the weak sunlight shining from above. This makes their silhouettes invisible to predators looking up at them.