The over 30-year-long autumn survey of the Glanville fritillary butterfly in the Åland Islands has contributed to the species becoming a globally known model organism in population biology. Thanks to the survey carried out every autumn, it is possible for us to observe long-term changes in the population dynamics of the butterfly. Over the years, the meadow network of the Åland Islands has proven to be a good environment for studying several phenomena in population biology. The diseases occurring on the butterfly’s main host plant, ribwort plantain, shed light on the development of epidemics in natural populations. The annual survey of powdery mildew on plantain is, on a global scale, a significant disease study conducted on wild plants.