Small Dark Yellow Underwing - Stuart Read

The Small Dark Yellow Underwing moth is very rare in the UK - it is only found in the central and eastern Scottish Highlands and even there is rarely seen.

In recent years there have been only a handful of sightings, leading to concern that this species might become extinct in the UK.

The adult moths are found on well-drained moorland with lots of bearberry and patches of bare ground below 650m altitude. Since this habitat is not uncommon, other factors are limiting the moth. In order to find out more about what it needs, we wanted to find exactly where its caterpillars feed.

It is known that they feed on bearberry (and possibly other plants), but since caterpillars of this moth had never been found in the wild in Scotland, their discovery might be key to determine more precisely the conditions they require. 

Dr Tom Prescott, Senior Conservation Officer with Butterfly Conservation Scotland and based in Kingussie, initiated a search for Small Dark Yellow Underwing caterpillars in 2017 at an estate near Carrbridge, which has been one of the most regular sites for recording adults in recent years.

The caterpillars actively feed at night but hide up during the day and so the search was conducted at night using torches. Unfortunately, no caterpillars were found.

For this year’s search, Tom brought in a secret weapon….Bugvac.

Bugvac - Highland Branch
Bugvac in action!

This is akin to a leaf blower in reverse and specifically designed to safely sample invertebrates by sucking them out of their hiding places amongst vegetation.

On June 22nd, an impressive 14 people gathered on the moorland edge, armed with washing-up bowls.

Highland Branch volunteers

The Bugvac was employed on clumps of bearberry and then the collected samples were tipped out into people’s washing-up bowls so they could sift through the catch.

The search hadn’t been going for long when a shout went up – Margaret Currie, a moth enthusiast who had travelled down from Culbokie to help the search, had found a Small Dark Yellow Underwing moth caterpillar in her bowl, thereby making history!

The spot was marked, photos were taken (only of the caterpillar, Margaret was too shy) and it was back to the Bugvac to find more, buoyed up by the successful find. However, although the Bugvac was used all day, no more caterpillars were found.

Small Dark Yellow Underwing Caterpillar
Small Dark Yellow Underwing Caterpillar

It’s hard to draw many conclusions of ecological requirements from only one caterpillar but one was better than none and at least a start has been made. Perhaps Bugvac will make another appearance in 2020 to gather more caterpillars and more information.

Pete Moore