Black widow spiders are color-coded to deter predators without tipping off prey

Secret codes and hidden messages aren't just for computer security experts or kids passing notes in class -- animals use them too. The telltale red hourglass of the black widow spider appears brighter and more contrasting to birds than to insects, finds a new study. The red-and-black color combination sends a 'beware!' signal to predators without scaring off their prey.