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Caithness Biodiversity Group helps conserve rare small blue butterfly as part of 'small is beautiful project'


By David G Scott

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A team of volunteers has been working hard to revive numbers of a rare butterfly at various locations in the county.

Caithness Biodiversity Group (CBG) has been working at sites around Dunnet, Castlehill and Scrabster to remove invasive plants and replace them with species that the small blue butterfly will thrive on.

Small blue drying its wings.
Small blue drying its wings.

Caithness has three known colonies of small blue butterflies on its north coast – the most northerly in Scotland. The small blue is a Scottish Biodiversity Action Plan species and is of conservation concern. In a past project, funded by a landfill grant, the CBG planted kidney vetch at Scrabster harbour adjacent to a small blue site and erected an interpretive panel. The vetch took well to the site and small blue have used the food plant.

Small blue on kidney vetch.
Small blue on kidney vetch.

There have been setbacks at the site and Mary Legg from the group said: "Unfortunately many of the previous vetch plantings have been lost – covered in stone cobbles or weed killing of the kidney vetch areas – due to changes in how the harbour is using the land with the new developments."

Phil Davey, the Caithness butterfly recorder, found fewer small blue butterflies on an abundance count than the 25 found in 2018. A count in 2021 found most along the area of vetch east of the yacht club.

Some kidney vetch has also been added to the strip of wild flowers growing along the lighthouse track with help and permission from the landowners there.

Work carried out at the Castlehill roundabout near Castletown.
Work carried out at the Castlehill roundabout near Castletown.

The CBG continues to work towards increasing numbers of the small blue butterfly at the three locations as part of its “small is beautiful project”. The group is also growing a variety of plants to support bumble bees as well.

At Castlehill the CBG cleared invasive Chinese bramble and cotoneaster from an old flagstone quarry face in what the group calls a "work in progress".

Another area of Castlehill at a quarry face where invasive species of plants have been replaced to create a habitat where the small blue butterfly will flourish.
Another area of Castlehill at a quarry face where invasive species of plants have been replaced to create a habitat where the small blue butterfly will flourish.

"Gunns of Lybster donated some stone chippings as we are experimenting with habitat creation," said Mary.

Recent work carried out at Castlehill includes:

  • Tidying up the wild flower and shrub roundabouts.
  • Scything and raking the two verges (no council cut took place last autumn).
  • Planting vetch and removing moss at the quarry spoil heaps.
  • Cleaning the quarry face removing moss and rank grasses.
  • Improving the rough path below the quarry face.
  • Pulling out and removing more invasive Chinese bramble.

"There was no regular butterfly monitoring carried out this year due to Covid," said Mary. "The kidney vetch is thriving in this area and bumbles bees and small blue are present in 2021. An abundance count has still to be carried out."

Small blue butterfly mating.
Small blue butterfly mating.

At another site along sand dunes in Dunnet, an abundance count turned up 50 small blues in a hollow area, 30 west of the hollow up to a small stream and eight west of a burn.

Caithness Countryside Volunteers planned a session clearing out moss from the dune hollow in early spring to improve the conditions for the kidney vetch to seed but this was cancelled due to Covid restrictions.

For more information on CBG visit its website at www.caithnessbiodiversity.org.uk/

Related article:

Launch of Highland Nature bodes well for Caithness bees and butterflies


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