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28 Aug 2020

Moths of Ben Lawers

Written by Helen Cole, Senior Ranger
Male emperor moth on straw. It has prominent eyespots on its forewings and hindwings.
Male emperor moth (Saturnia pavonia)
Ben Lawers National Nature Reserve is rightly renowned for its flora, which provides habitats for a diverse range of invertebrate fauna, including moths.

Closely related to butterflies, these lesser known Lepidoptera have a vital role in the ecosystem as pollinators and food for birds and other animals. One of the first indicators of the success of our pioneering habitat restoration was an increase in moths and their caterpillars.

Many of the moths at Ben Lawers disprove common misconceptions that they’re dull and fly at night. The male emperor moth (Saturnia pavonia), Britain’s only member of the silk moth family, flies in sunshine during April and May and the larger females can be found at rest on the vegetation. Both sexes have large eyespots on both forewings and hindwings, although the obvious conclusion that these are to deter predators is not proven. The feathery antennae of males detect chemical signals released by females at great distances.

Another day flier, sometimes in very large numbers, is the northern eggar (Lasiocampa quercus), named after the egg shape of its cocoon. Known in southern Britain as the oak eggar, northern specimens (form callunae) are larger with stronger colouration and an extended life cycle. Here, the caterpillars take two years to fully develop before pupation. Large, brown and hairy, they’re frequently seen on the main footpaths and can occur in plague proportions, defoliating trees – in contrast to the adults, which don’t feed at all.

Brown hairy caterpillar on a green leaf.
Caterpillar of the northern eggar (Lasiocampa quercus)

Despite flying in warm sunshine, the narrow-bordered bee hawk-moth (Hemaris tityus) is less easy to spot, partly because it’s less common but also as it can be mistaken for a bumblebee. It uses mimicry as protection from predation, but observation reveals that, unlike bumblebees, it doesn’t alight to feed but hovers close to flowers with tube-like flowers such as bugle (Ajuga reptans). It’s also faster and more agile in flight.

Narrow-bordered bee hawk-moth flying close to a flower.
Narrow-bordered bee hawk-moth (Hemaris tityus)

Other diurnal – literally ‘of the day’ – species include the true lover’s knot (Lycophotia porphyrea), a small moth named after the double loop on each forewing, which is a symbol of love and friendship. These intricate black and white markings on a background colour that may be quite pink make it well camouflaged against the heathers on which it feeds. The antler moth (Cerapteryx graminis) is on the wing from mid-July to September and flies during the day in warm weather as well as at night. It’s named after the ever-present marks on its wing, reminiscent of antlers. The females scatter eggs over the grassland where they hatch the following spring, the caterpillars providing a great source of food for birds.

A small number of species are only found at altitudes above 600m. The broad-bordered white underwing (Anarta melanopa) is nationally scarce and, until recently, was last recorded on Ben Lawers in 1932. It flies fast, often low to the ground, in sunshine or even just sunny intervals from mid-May to June, feeding on the flowers of montane species including cowberry (Vaccinium vitis-idaea) and blaeberry (Vaccinium myrtillus). The caterpillars feed at night on these and other dwarf shrubs, and recent data suggests that this moth may be more widespread than previously thought.

Broad-bordered white underwing moth camouflaged against its background of vegetation.
Broad-bordered white underwing (Anarta melanopa)

Not all diurnal moths are easy to see, some being very small. For convenience when identifying them, moths are divided into micros and macros, and as the terms suggest, the micros are smaller. They also tend to be more primitive in evolutionary terms and many don’t have common names.

The day-flying micro moth Micropterix aureatella is one of a family of very small primitive moths, which are unusual in having chewing mouthparts and as adults feed on the pollen of herbaceous plants. Their metallic purple forewings are only 4mm long and held tent-like over the body. This species flies from May to early July and is recorded as feeding particularly on sedges.

Close-up of a Micropterix aureatella moth on a person's arm.
Micropterix aureatella

One of the rarest moths found at Ben Lawers is the mountain plume (Stenoptilia islandicus), which is not known anywhere else in the UK. Until recently, we thought it only occurred at a single small location on the slopes of Meall nan Tarmachan, where the larvae feed on mossy saxifrage (Saxifraga hypnoides), but after careful searching it’s now been recorded at seven locations. It’s one of a family of moths characterised by their long, narrow wings held at right angles to the body, which is also long and thin.

Mountain plume moth on alchemilla plant.
Mountain plume (Stenoptilia islandicus)

Whilst we can record day-flying moths and caterpillars in the field, many species are nocturnal. These are surveyed using harmless light traps, and we hold events where it’s possible to see the moths caught overnight and appreciate their beauty and diversity.

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