>> Backround information

Development

Eight Finnish butterfly species can be regarded as mire specialists. More than 65 000 observations of these have been recorded into the National Butterfly Recording Scheme in Finland (NAFI) since it was started in 1991. These come from a total of 885 observation squares, each 10 x 10 km in size.

One or more mire species were reported from 532 squares in the 1990s and from 492 squares in the 2000s (-8%). The distribution area of Finnish mire butterflies appears to have shrunken especially in southern Finland where mire butterflies have been reported only from approximately half of the squares of the early 1990s. Partially, the declining trend may also be  explained by changes in observation activity.

Although the stronghold of mire butterfly populations is in the northern parts of the country, less observations accumulate from there compared to more southern districts. Of the approximately 500 annual squares 14% are located in northern Finland, 26% in central Finland and 60% in Southern Finland. The declining trend in the distribution area of mire butterflies in northern Finland is therefore more uncertain than the trends in central and southern Finland.

Mire butterflies

Eight of the altogether 122 day-active Finnish butterfly species occur predominantly on mires. These species can be roughly grouped into two based on their distribution area and abundance. The first group consists of four relatively common mire species, which are still quite widespread also in central and southern Finland. These are Bog Fritillary, Cranberry Fritillary, Baltic Grayling and Large Heath.

The second group consists of species with a more northern distribution. The most abundant of these are Zig-zag Fritillary and Willow-bog Fritillary, which are absent from the southern coast and Åland Islands. The Lapland Ringlet flies solely in odd years in the southern parts of its range. The Grizzled Skipper is clearly the rarest of these species although it has been recorded almost in the whole country. The species in this group have been observed to decline most rapidly after the draining of pristine mires.

Some other butterfly species also occur on pine mires and fen edges, but these are more generalist in their habitat preference. The most common are Moorland Clouded Yellow, Green Hairstreak, Cranberry Blue and Pearl-bordered Fritillary. Especially in the northern parts of the country these species also thrive in woodlands and other habitats. As the draining of mires increases tree growth these species may even benefit from draining activities. The Disa Alpine, which flies only in northern Finland, is another typical species occurring on mires with tree cover.