The Apollo butterfly, Parnassius apollo, is categorized as Near Threatened (NT) in IUCN Red List. Today in Sweden it is found only in strongly fragmentized populations. In the county of Stockholm, P. apollo exists exclusively in some islands of the archipelago and with one mainland population in Stora Vika. This study has the purpose of expanding the knowledge of the local conditions for the butterfly in the south parts of the county of Stockholm and thereby contributes to a sustainable land management that can preserve the Apollo butterfly.

A comparative study was done between areas where the butterfly today have: a stable population (Stora Vika, Utö and Ålö), has disappeared (Muskö and Yxlö) or is strongly declining (north part of Ornö). The investigation was based on factors that was considered be contributing to the species decline. Factors that was investigated was the general distribution of host-plant S. telephium, overgrowth in rocky outcrops, presence of nectar plants close to host-plants and if a large proportion of forest in the surroundings of the investigation sites could have a isolating impact on sites. The study was based on 10 sites where the butterfly exist, 7 sites where it has disappeared and 3 sites where it has declined. No significant differences could be found for any factor. On the contrary, the general presence of host-plants at rocky outcrops seems to be the same in areas where the butterfly has disappeared as in areas where it exist today. However caterpillars were only found at sites with a wide distribution of host-plants and also at sites with a large proportion of forest in the surroundings. This was speaking against the hypothesis that a large proportion of forest could have an isolating effect on sites and therefore a negative impact on the adult butterfly preferences.

The result creates new questions and the conclusion is that more knowledge of the local conditions is needed to ensure good practice in land management. Sites which are today hosted by the caterpillar should be identified, investigated and protected. Furthermore should the dispersal of nectar plants be investigated and it would be interesting to study the effects of limestone by analyzing and compare Cd concentrations in S. telephium from Muskö with plants from Stora Vika, Utö and Ålö.