Grassland management for butterflies

More than 20 butterfly species regularly breed in Suffolk on suitable grassland and field edge habitat including species-rich pasture, rough grass margins and nettle patches on field edges and awkward corners, scrub, woodland and hedges.

Species-rich grassland provides food for developing larvae on grasses and flowering plants, while nectar-filled flowers feed adult butterflies, moths and other insects. But with careful management and by ensuring there are good nectar sources within reach, even fairly species-poor grassland can be invaluable to certain butterflies whose larvae feed on grasses.

A grassland 'mosaic'

Butterflies require a varied topography and a habitat that can sustain them throughout the year. A grassland mosaic should include:

• Patches of bare ground – some butterflies require sunbaked bare ground for basking in

• Short open turf – essential for non-competitive host plants such as birds’ foot trefoil

• Tall grass – small and large skippers will lay eggs on grass such as cocksfoot and many species over-winter in grass sheaths

• Tussocks – Yorkshire fog and cocksfoot are eaten by caterpillars of speckled wood and wall brown butterflies(and many others) and tussocks provide essential over-wintering cover

• Plants in all stages of development ie flowering for nectaring and with dead seed heads and stems for some species to over-winter in

• Ideally, nearby scrub or hedges – on which the adults feed, rest, sunbathe and use as a corridor, linking different areas of suitable habitat.

• A nectar-rich food source over a long season, provided by varied trees, shrubs and flowering plants in a range of nearby habitats

• Good, undisturbed egg-laying habitat – tips of grasses, flowering plants and shrubs that won’t get cut or browsed before eggs have hatched and developed successfully

• Plant diversity and structure is important – many species will only lay their eggs on a particular food plant. The larvae of the whites feed on a range of cruciferous plants, whilst the blues and copper require more specific, and often rarer, larval food plants. The larvae of the various browns and skippers feed on relatively common grasses in hedge bottoms, and then depend on flower and shrub nectar as adults. Nettle
feeders often hibernate as adults in hollow trees and wood piles along hedgerows

• A varied topography is beneficial such as provided by ant-hills and old earthworks, providing warm southfacing slopes and sheltered areas.

Continuity of management

Avoid sudden management changes. Crucially, deciding how to manage an area of grassland should take account of the site’s management history. Grazing or cutting favours different plants and therefore associated butterflies and moths. Over time with the same annual management, a community of plants and insects will have adapted to suit this regime.

Suddenly changing this regime, even for just a year, may irreversibly harm a butterfly or moth species – and still not actually encourage a greater diversity in its place. If conditions become unsuitable for a species, even for only a few months, then that species can become extinct on that site, especially if there is no suitable corridor along which to re-colonise from elsewhere.

Hay meadows and mowing

Hay meadow management is excellent for flowering plants, but for butterflies the hay cut can be catastrophic. The cut removes both nectar-rich adult food plants and plants on which eggs may have been laid and larvae are feeding. The small copper survives hay meadow management by having several broods a year. The first brood is laid on large tender sorrel leaves growing in long grass but subsequent broods are laid on small sorrel plants in the aftermath of a hay crop.

• Where mowing is the only option, cuttings should always be removed (to avoid a mulching, enriching and smothering effect), ideally as a late hay crop (mid- July).

• Some areas (up to one third) should always be left uncut each year to continue to provide some nectar, to allow a proportion of butterflies to complete their life cycle and to provide over-wintering areas. To prevent scrub encroachment from hedges this uncut area can be rotated around or alternated each year.

• If possible find out the traditional date for cutting your site before changing it, as doing so may completely change the plant community and thus the associated invertebrates. A late hay cut in mid-July is probably the least damaging for butterflies. But it may be better to cut part of the meadow earlier in June and cut the second part later in July to ensure some continuity of flowering plants (essential nectar) and some standing seed heads and stems over winter.

Grazing management

Choosing the appropriate grazing animal, stocking level and timing of grazing is dependent on many site factors. Be cautious – it is better to trial-graze small areas or under-graze a whole site, assess the impact and then adjust management, than to ‘blitz’ a site and possibly cause local extinctions. Ideally, aim to create a varied sward where a proportion of the tussocks, standing dead seed heads and some plant litter should still remain at the end of the grazing period.

Grazing at a low stocking density (less than one cow per hectare or between one and three sheep per hectare ha) is a gradual process that avoids sudden, drastic changes to a site and can produce a patchwork grassland required by different butterflies ensuring a longer season of larval food plants and adult nectaring plants. See the table below for grazing management options on different sites.

Cattle grazing is usually preferable to sheep grazing as cattle’s selective browsing produces a better patchwork of varied sward height. Rotational grazing with tethered sheep or goats can produce the same effect within small areas but untethered tend to produce a more uniform and less beneficial sward.

Horses produce enriched latrine areas and hard-graze elsewhere and are thus more suited to grazing large complex areas at a relatively low stocking density.

Grazing management to benefit butterflies on different grassland sites

Management option	Suitable site	Grazing objective	Benefits to butterflies
Winter grazing (October to March)	Infertile, dry sites prone to drought Sites grazed by rabbits in summer months	At the end of the grazing period a proportion of the tussocks, standing dead seed heads and some plant litter should still remain. They may appear ‘under-grazed’ to farmers	Keeps down coarse grasses, benefits uncompetitive plants. Least damage done to larval and pupal stages as they are dormant and tucked well down into cover
Early summer grazing	Wetter, more fertile soils which need rapid plant growth to be kept down	Keeps down coarse grasses, benefits uncompetitive plants which subsequently flower in late summer, providing good egg-laying sites and larval food plants
Light summer grazing	Only suitable if very light grazing only – on more fertile non-droughty site	Create diversity in sward height with plenty of flowering plants and tussocks. Fine tune grazing in periods of drought	Few benefits – heavy summer grazing can be very damaging to butterflies.
Rotational grazing (around compartments or tethered animals) – several times a year on fertile sites, less on infertile	Where site is divided into compartments but only suitable where larval and nectaring plants are evenly distributed.	Create diversity in sward height with plenty of flowering plants and tussocks in each compartment.	Allows mobile butterfly species to move to most suitable habitat and it can be finetuned to ensure there are always some flowering plants.
Light continuous grazing	Only suitable with light grazing on site with a diverse topography and habitat.	Create diversity in sward height, light enough grazing to allow plenty of flowering plants and tussocks in summer. Fine-tune during drought.	Keeps down coarse grasses but on a flat fertile site a uniform sward will probably result. Can produce a varied sward.
Opportunistic grazing to ‘blitz’ a rank site	Only suitable as part of a careful management plan.	Botanical objectives may outweigh invertebrate priorities.	May benefit flora but may eliminate insects. With good habitat links, butterflies may re-colonise.