Abstract: In coastal dunes of The Netherlands, an infection of the fungus Pandora myrmecophaga (Turian & Wuest, 1969) Keller & Petrini, 2005 was observed in a population of Formica rufa Linnaeus, 1761. The parasitic fungus causes a behaviour in the ant that has been described as summit disease. Pandora myrmecophaga infections have been reported onlyfrom Formica species and I could not detect summit disease in other ant species. Based on field and laboratory observations, details of the behaviour of infected Formica rufa workers are presented, largely confirming earlier observations, but adding new insight.