The American lobster, Homarus americanus, supports a several hundred million dollar industry in the Northeast yet much of the basic information about its behavior is not known. Our overall research goal is to investigate the genetic and neural basis of behavior in this important marine crustacean. Lobsters are a good choice for investigations into the molecular basis of circadian rhythms because of their robust circadian rhythms of locomotion. Our basic findings were that lobsters exhibit robust daily and circadian rhythms of locomotion as well as heart rate rhythms. Interestingly, long thought to be generally nocturnal, they may be more diurnally active in the field depending on location.