Unfit or unlucky? A sexual difference in the timing of adult emergence in the glow-worm Lampyris noctiluca L. (Coleoptera: Lampyridae)

Abstract

Counts of male and female glow-worms conducted on the same site over five years exhibit a consistent seasonal pattern, with a relatively rapid increase in the number of females, followed by a more gradual and protracted decline. The results also reveal a distinct and previously unreported seasonal shift in the apparent ratio of males and females, with males becoming relatively scarcer and virtually disappearing altogether by the final third of the female season. A possible explanation for this difference in timing is suggested in terms of a balance between the selection pressure for increased female body size and the uncertainty of achieving the necessary growth rate in an unpredictable environment.