Generation cycles, population cycles with a period of approximately one generation, have been observed in a variety of field and laboratory studies. Such dynamics are predicted to arise through the effects of resource competition and cannibalism or involve consumer–natural enemy interactions. We first show, using a new highly simplified model, that generation cycles are a very common outcome of strongly age–structured intraspecific interactions involving cannibalism. We then analyse a series of unique long–term time–series of ladybeetle (Coccinellidae) abundances from tropical Indonesia. Some of the time–series display clear generation cycles, and we argue that there is strong evidence that these are caused by intraspecific cannibalism.