Lillsjöbäcken, Naturreservat

The Lillsjöbäcken nature reserve has one of the county's finest populations of river pearl mussel. The rare net butterflies ash net, wet net and soot net butterflies also fly here. In ancient times, the stream's water power was used at Järlehyttan to produce iron. Because of the rare river pearl mussel and the unusual net butterflies that live here, the reserve is part of the EU's network of protected areas, Natura 2000.

Long stream course

From Lillsjön in the north, Lillsjöbäcken lowers in the form of rapids, falls and shorter stretches of calm water, towards lower and lower levels, to flow together with Järleån just downstream of Hammarby. In the south, the area borders the nature reserve Utterbäcken.

Pearl mussels and rare net butterflies

In Lillsjöbäcken there are plenty of river pearl mussels of different ages, which shows that new mussels are being produced. This indicates that the habitat is also good for trout. The larvae of the river pearl mussel live as parasites on the gills of the trout for about nine months. The reserve is also home to the rare net butterflies, the ash net butterfly, the wick net butterfly and the soot net butterfly. The ash net butterfly lays its eggs only on ash trees or olive bushes. The butterfly has a life cycle of 2-4 years, as the caterpillars only feed on the ash or olive buds just as they are opening. They then migrate to the ground where they rest until the buds open the following year. The meadow butterfly lays its eggs on the leaves of meadowsweet. In the fall, the larvae weave a web in which they overwinter and then hatch in early summer. The sooty moth feeds on meadow rue. The stream ravine in the south has calcareous moraine, which means that species such as witch hazel, water lily, common ragwort, columbine and sub-violet thrive there.

Cultural remains along the stream

In the southern part of the reserve are the remains of Järlehyttan. Iron was manufactured here from at least the 16th century until well into the 18th century. The remains consist of a ruin of the ironworks, a dam and a slag heap (slag is a glassy "rubbish stone" left over from iron production). Slag residues are also found in the stream channel south of the smelter and at a site by the Mellanbron bridge north of the smelter. It is possible that iron was also produced at Mellanbron at some time. South of Järlehyttan there was still a croft, Finnafallet, in the mid-20th century. The site is located next to the reserve in the far south. The land around Järlehyttan was cultivated well into the 20th century, and further back the stream around the ironworks was lined with meadows that provided hay for the animals. To reach the forests east of the stream, several roads have been built at different times and simple bridges have been built over the stream.

Accessibility

Lillsjöbäcken belongs to level 1 in the County Administrative Board's leveling of the county's nature reserves, which means that the reserve lacks outdoor recreation facilities.

Read more about the leveling and management of protected nature