organisms may exhibit rhythmic physiology, for these organisms the dominant rhythm is unlikely to be circadian. For east-west migratory organisms—and especially those organisms that circumnavigate the globe—the absolute 24-hour phase might deviate over months, seasons, or years. Some spiders exhibit unusually long or short circadian clocks. Some trashline orbweavers, for example, have 18.5-hour circadian clocks, but are still able to entrain to a 24-hour cycle. This adaptation may help the spiders avoid predators by allowing them to be most active before sunrise. Black widows' clocks are arrhythmic, perhaps due to their preference for dark environments. See also Chemical clock Chemical oscillator References External links Circadian screen search Circadian rhythm Oscillation