A parthenogenetically reproducing Collembolan,Folsomia Candida,shows a cir‐caseptan (approximately 7‐day) oviposition pattern under conditions of continuous darkness at 25°C Growth was faster, size larger, and mortality lower for insects kept in continuous darkness, as compared to those on an alternating L/D12/12 lighting regimen. The circaseptan rhythm here documented for an invertebrate can be compared with rhythms of similar frequency in man and rat, although the as yet unknown underlying mechanisms are likely to differ.