The Biorhythms of Spiders

Abstract

Changes in the physiology and behaviour of living organisms usually take place cyclically or rhythmically. This is as true of spiders as it is of all other animals and plants. Some innate rhythms, such as that of the beating of the heart, have short periods. At the opposite extreme, endogenous or persistent rhythms with a periodicity of about a year have been shown experimentally to exist in a number of long-lived plant and animal species. Rhythmic functions of ecological significance in animals are mainly of three kinds: endogenous daily, lunar and seasonal or annual rhythms; photoperiodic phenomena; and the sense of time used in celestial navigation. Endogenous or `persistent’ daily biorhythms, which free-run with a circadian period are widespread among spiders. Circalunar activity rhythms do not appear to have been much investigated, since most species do not live long enough to exhibit endogenous circannual rhythms. Although these may occur among Mygalomorphae, and especially in Theraphosidae, the possibility of their existence has not yet been tested. Until now, although the autecology of phenology of many orders of arachnids have been investigated, no evidence of a circannual clock has ever been reported, even in the most long-lived species (CloudsleyThompson 1978).