Butterflies have very specific food and habitat requirements at different stages of their life cycle. They are therefore particularly sensitive to modifications of their environment and serve as an excellent indicator of the status of the ecosystems. They are especially sensitive to changes in habitat management such as overgrazing, undergrazing or changes in forestry practice. More than half of the butterfly species inhabit grasslands, woodland and scrub are home to about a quarter of the species, while the rest are found in other types of ecosystems (rocky slopes, etc.).
The major drivers of butterfly habitat loss and degradation are related to agricultural intensification, for example through conversion of grasslands to crop fields, the improvement of flower-rich grasslands, drainage of wetlands, and the intensification of livestock grazing. While agricultural intensification tends to take place on more productive land, the decline of traditional patterns of agriculture on more marginal areas leads to abandonment of land and to the subsequent invasion of shrubs and trees (especially in eastern Europe and in the Mediterranean). This trend is affecting a wide range of wildlife groups and is considered to be the second major threat to European butterflies, affecting species such as Phengaris arion, Lycaena helle and Colias myrmidone.
Climate change is already impacting some populations (in particular of tundra species like Colias hecla and Euphydryas iduna) and is likely to affect additional species more significantly in the future. Climate is a major factor determining the distribution of species (biogeography), as well as the distribution of the plant vegetation. Climate change may simply shift these distributions but, for a number of reasons, plants and animals may not be able to keep track of these changes. The pace of climate change will almost certainly be more rapid than most plants are able to migrate. The presence of roads, cities, and other barriers associated with human presence may provide no opportunity for distributional shifts. For this reason, there is likely to be a serious mismatch between the future climatic zones that are suitable for butterflies and their main foodplants.
Changes in the management of woodlands and non-agricultural areas, such as grasslands, are also important threats. In some cases, land-use changes, even under AgriEnvironmental Schemes, and unfavourable grassland management (wrong timing or intensity) have led to drastic declines.
On islands (such as the Canary Islands or Madeira), as well as in the Mediterranean, the increased frequency and intensity of fires, the development of tourism activities and urbanisation destroy the habitat to which the species are bound, such as the laurel forest.
Pesticides and herbicides kill both adult butterflies and caterpillars, some of them being targeted as “pest” because their caterpillars eat farm crops, but other inoffensive species suffer the same fate. Furthermore, domestic and agricultural pollution (such as nitrogen deposition) leads to a faster succession of vegetation, thus reducing the area of suitable habitat and habitat connectivity substantially.
Increased presence of competitors or predators, as well as introduction of invasive species are also adding to the pressure the European butterflies are facing.