Enhancing Habitats for Butterflies and Moths

Enhancing Habitats for Butterflies and Moths

Scotland is home to 35 species of butterfly and around 1300 moths, including a number of rare species for which Scotland has the bulk, if not the entire, UK population. All species share the same four life-stages; egg, caterpillar, pupa and adult, however, each has a unique niche. Some of the differences may be subtle and for some species their exact requirements are unknown. 

Most butterflies and moths have four main requirements:

  1. Food for the caterpillars. For some species this is a single type of plant, although most species are not so restricted.
  2. Energy in the form of nectar from flowers for the adult. Many species have favoured nectar plants, but some moths do not feed at all in the adult stage.
  3. For butterflies and some day-flying moths, sunny, sheltered areas for adults to bask, warm-up and fly.  South-facing sheltered slopes are particularly important in Scotland. The caterpillars of some species also require a warm micro-climate in order to develop.
  4. Somewhere to over-winter safely - usually in taller vegetation, scrub or ivy.

Butterfly and moth populations can be very dynamic, being very common in some years but very scarce in others. They can also be very quick to respond to positive changes in land management, far more so than birds, plants or mammals. This is one of the reasons they can make excellent ‘indicator’ species.

Other important considerations include:

  • Manage at a landscape scale. Invertebrate populations are more robust if they are managed at a landscape scale. It is often important to improve connectivity between sites to allowing the exchange of adults between neighbouring colonies, minimising the chance of populations becoming too isolated.
  • Knowledge of species’ requirements. This is particularly important, particularly for rare and threatened species, as they can have exacting requirements for some of their life stages. Most species of butterfly and moth are also quite sedentary, so sites have to cater for all four life-cycle stages of the species throughout the year. If these are not provided for, then a species will not survive. This is in contrast to management for many birds where the habitat often only has to be suitable during the breeding season. 
  • Varied habitat structure. In general the more diverse a habitat the greater the range of butterflies and moths it will support. This is often best provided by appropriate livestock grazing. Light levels of seasonal grazing, particularly by cattle, can maintain and improve floristic diversity, providing a variety of larval foodplants and adult nectar plants. Structural diversity can also provide the essential warm micro-habitats that provided shelter as well as breeding areas. Topography can also be important eg south-facing hillsides or east-west running rides being the sunniest and warmest. Patches of short grass, bare ground or even bracken litter can also provide crucial warm micro-climates.

As part of the 2014-2020 Scottish Rural Development Programme (SRDP) it may be possible to obtain funding to manage habitats to benefit butterflies and moths. This is primarily through two schemes; the Agri-Environment Climate Scheme for projects that promote conservation or tackle climate change, and the Forestry Grant Scheme for woodland management and creation.

Agri-Environment Climate Scheme  

This competitive scheme is open to farmers, groups of farmers and other land managers with land and who are registered with Rural Payments and Inspections Division. Under the scheme Marsh Fritillary is identified as a national priority, so if your application will directly benefit Marsh Fritillary you will be allocated points. An attempt has been made to target the Agri-Environment-Climate Scheme management options at areas where they will deliver the greatest benefit. There are many aspects to the scheme but two options that could be particularly beneficial to key Lepidoptera are Species-rich Grassland Management and Habitat Mosaic Management.

Species-rich Grassland Management

This option aims to benefit species-rich grassland habitats and a range of flowering plants, bees, butterflies, moths etc., by implementing appropriate grazing or cutting regimes. Careful grazing management, allowing the sward to grow longer in the summer will permit plants to flower and set seed. Butterflies and moths that could benefit from this option include Marsh Fritillary, Northern Brown Argus, Slender Scotch Burnet and Narrow-bordered Bee Hawk-moth. To be eligible land has to either be species-rich grassland, or restored or created species-rich grassland. 

Management can be through cutting, grazing, or a mixture of both. In most cases grazing alone is the most suitable management to benefit Lepidoptera. It is not possible to suggest a generic grazing regime that will suit all sites and species, but in most cases a late spring and/or early summer grazing break will be beneficial.

Restrictions on this option state you must not:

  • plough the area, except to aid establishment when creating species rich grassland on arable land
  • cultivate the area, except to aid establishment when creating or restoring a species-rich grassland
  •  fertiliser, slurry or farmyard manure
  • apply lime, unless you have prior approval
  • allow the land to become poached or vehicle tracked
  • carry out supplementary livestock feeding unless with prior written approval
  • spray, except for the spot-treatment of injurious weeds or treatment of invasive species (requires prior written notification/approval)
  • you must also maintain a diary

Habitat Mosaic Management

The aim of this option is to maintain and improve areas of farmland that are made up of a patchwork or mosaic of traditional semi-natural habitats that need to be managed as a single unit. Habitat mosaics may include wetland, wet grassland, species-rich grassland, unimproved grassland, semi-improved grassland, tall-herb communities, scrub, heathland and scattered pockets of woodland or wood pasture amongst others. This option can benefit a wide range of key Lepidoptera including Argent & Sable, Marsh Fritillary, Forester moth and Narrow-bordered Bee Hawk-moth.

Careful grazing management is often the key to successfully implementing this option and as, for species-rich grassland, requires the adoption and adherence to an approved grazing regime that defines livestock units and dates. You must not:

  • apply fertiliser, slurry or farmyard manure
  • apply lime, unless you have prior approval
  • allow the land to become poached or vehicle tracked
  • carry out supplementary livestock feeding unless with prior written approval
  • spray, except for the spot-treatment of injurious weeds (requires prior written notification) or treatment of invasive species (requires prior written approval)
  • you must also maintain a diary

Forestry Grant Scheme

The Forestry Grant Scheme provides funding for the creation of new woodlands and the sustainable management of existing woodlands under eight categories. There are many aspects to the scheme but options under two of the categories, Woodland Improvement Grant and Sustainable Management of Forests can be particularly beneficial to key Lepidoptera, particularly to the two priority butterflies identified in the Scottish Forestry Strategy, Chequered Skipper and Pearl-bordered Fritillary. This advice, therefore, focuses on these two woodland glade/edge species and three key management tools, scrub control, woodland grazing and bracken control.

Pearl-bordered Fritillary both open, sunny but sheltered habitats, which are often provided by glades, rides or along woodland edges. This can be an ephemeral habitat with conditions slowly deteriorating as woodland cover increases. The maintenance and creation of open spaces are very important, and management has to be planned carefully to ensure that sufficient suitable habitat is always present and that open spaces are linked.

In most cases an approved Management or Forest Plan is required under the Forestry Grant Scheme.

Woodland Grazing

Many colonies of both species are maintained by extensive grazing, particularly by cattle and deer. This keeps sites open and flower-rich. Their trampling can reduce the accumulation of dense bracken litter and also creates bare ground as germination sites for nectar plants and violets, the latter being the larval food plant of the Pearl-bordered Fritillary. The best conditions are achieved either by all year light grazing, or seasonal grazing with a reduced spring/summer stocking rate. Such a regime should also lessen the need for regular scrub clearance by keeping tree regeneration in check.

Woodland Grazing requires a Management Plan approved as per the Woodland Grazing Toolbox. The plan must be tailored to an individual woodland to reflect woodland type, grazing history and site-specific management objectives. The plan must also describe the expected environmental impact of the livestock grazing.

Scrub control

In the absence of grazing and browsing from either deer or livestock, suitable habitat is best maintained through carefully planned and targeted woodland or scrub management. Ideally scrub should be cleared once 50% of glades or open space is covered with scrub over 1.5m high. Scrub cutting should be cyclical, occurring on a rotation of 3-10 years dependent on site conditions. At large sites the cutting of scrub should be staggered to produce open spaces at different stages of succession. 

Ideally rides and paths should run east-west as such rides have a greater proportion of warmer south-facing edges. Around 25-30m wide is the perfect width for them still to be sunny, yet sheltered. The inclusion of scalloped bays (c. 25m across) at intervals along the south-facing edge will provide additional sheltered sunny habitat. This also applies to powerline wayleaves through woodland as they often support both Chequered Skipper and Pearl-bordered Fritillary colonies by providing suitable sheltered, open habitat, and their continuous linear nature means that they act as corridors to link neighbouring colonies. Glades should be at least 30m wide in sunny sheltered locations but not so big that they are too open and provide little shelter.

This can be achieved under the Scrub/Woody Vegetation Eradication option which is available for the eradication of scrub or woody vegetation for the purpose of habitat restoration, and/or to encourage natural regeneration, or for public access. Payment rates are dictated by the density of scrub.

Bracken control

Before any bracken control is undertaken it is vital that an assessment is undertaken to ensure that good quality Pearl-bordered Fritillary habitat is not targeted. Sites are best assessed in the spring before the bracken fronds have unfurled. Suitable habitat is often characterised by violets growing in shallow bracken litter (<15cm depth) and low to medium bracken density (<c20 fronds m2), in sunny, sheltered locations. Steep south-facing sites are the most important. Bracken control should not be undertaken in areas of suitable habitat. Where control is considered necessary to benefit Pearl-bordeerd Fritillary, the aim should be to reduce both the density of bracken and the depth of the litter, rather than to eradicate it. 

The following options are available for treatment under the Forestry Grant Scheme.

  • Chemical treatment – spraying must use an approved chemical for bracken control.
  • Mechanical treatment – bracken should be controlled using machines with appropriate fittings to cut, roll, or flail. Control must be undertaken at least twice during the growing season.
  • Manual treatment – bracken should be whipped early in the growing season to sever the tender young bracken fronds before they harden off.