The phenology of Ophrys sphegodes (the early spider orchid): what annual censuses can miss

Ophrys sphegodes is a rare species in the United Kingdom. The largest extant population of the species, at Castle Hill National Nature Reserve in Sussex, has been monitored each year since 1975. At each annual census, which is conducted during the peak period of flowering (May), the co‐ordinates of each plant are recorded, allowing the fate of individuals to be followed from one census to the next. In the present study the population was monitored throughout one complete year. The data collected allow the phenology of the species to be described and the effectiveness of the annual census to be assessed. The study shows that a substantial number of Ophrys sphegodes plants emerge above ground and re‐enter the below ground phase before the census date. These results suggest that reliance on annual census records alone may result in the size of the population being underestimated and incorrect life‐histories being ascribed to individual plants. True counts of the population may be obtained only if ‘dormant’ plants are retrospectively added to the population.