Bromley biodiversity species action plan: White Admiral butterfly

The White Admiral (Limenitis camilla) is a woodland species which is prone to significant year-to-year fluctuations in population numbers. This butterfly has only one food plant, which is native honeysuckle (Lonicera periclymenum). It is this plant and its immediate environment that should be managed to support known local colonies and to encourage the spread of the species across the borough into new sites.

Changes to woodland management have impacted many woodland butterflies with white admiral being a rare beneficiary from the decline in coppicing practice over the past 150 years. A modern less regimented coppicing management strategy results in a more natural woodland which facilitates the growth of honeysuckle in partly shady areas at woodland edges. It is therefore something of a balancing act to maintain a patchwork of open glades with woodland edge but still promoting the growth of honeysuckle.

It is thought that summer temperature while the larvae are feeding is an important factor in population numbers. A cold early summer will result in slow development of the caterpillars that can be found by foraging birds. If the local climate through the period of May and June is warm, they feed quickly through to pupation and good flush of summer butterflies results.

Life cycle

The butterfly spends the majority of its life in the larval stage typically starting at the beginning of July through to the middle of June in the following summer. A partial second brood in late summer is sometimes observed in good years. Single eggs are laid at the edge of the upper surface of honeysuckle in July and August at a height of less than 2 metres from the ground (Pollard, 1979, pp 61-74). After a week the caterpillar hatches and starts to feed on the tip of the leaf leaving the central mid-rib. This stage of the life cycle is a good time to search for the presence of larvae as the feeding signs are conspicuous and characteristic of this species.

If a single leaf is large enough, this alone may be sufficient to feed a larva through to the third instar at which point it will over-winter in a hibernaculum formed by rolling a fragment of remaining leaf (Maitland et,1989, pp.183-185). Removal of any dangling honeysuckle with tenanted hibernacula over the winter through coppicing and glade clearance or maintenance will also remove the larvae which would have provided the next year’s crop of butterflies. After hibernation, feeding resumes until pupation at the end of May to the beginning of June. Pupation is usually at the underside of a leaf and lasts two to three weeks. Adults are on the wing from late June until early August. Brambles are a favoured nectar source but animal faeces and aphid honeydew are also visited (Lederer,1960, pp 521–546).

Habitat and management guidance. (butterfly conservation, 2020)

White admiral form discrete colonies within suitable blocks of woodland habitat and typically these occur at low densities with rarely more than two or three butterflies seen at a time. In woodlands with several kilometres of suitable ride edge, up to 50 adults may be encountered if the colony is strong and well established. Within the main part of their national range many colonies have become isolated due to habitat loss. The mobility of adults has not been studied in detail, but the spread of the butterfly during the twentieth century indicates that it can colonize over distances of many kilometres. Between the 1920s and the 1930s, the distribution extended by distances up to 100km, implying an average spread of up to 10km per year (Asher et al., 2001, pp 185-187). This mobility is also indicated by individual sightings some kilometres from known colonies (Butterfly Conservation, 2020). This observation would suggest that butterflies should be able to quickly spread to occupy new habitat if the required habitat is provided. Honeysuckle strands dangling down from trees or shrubs in partial shade provide the ideal larval feeding habitat and Bromley’s Friends groups should be instructed to conserve any plants where possible when coppicing woodland and clearing rides.

General habitat

The butterfly may be encountered in deciduous, mixed deciduous/coniferous and coniferous woodland which have often been neglected or are mature.Short-rotation coppice is not typically colonized as the food plant cannot become permanently established. Both young thicket stage and mature conifers can support suitable honeysuckle growth, but these can be absent from some broad leaved woodlands, notably ash and beech. More specifically there is a requirement for shady woodland and ride edges where there are sunny glades with patches of bramble that are used for nectaring.This habitat can be enhanced by encouraging a belt of broad leaved trees where honeysuckle can flourish in the ride edges.

Coppice and timber plantations

Attempt to retain mature woodland or over-mature coppice blocks although dense over-mature woodlands with few sunny rides and glades are unsuitable. Control of deer, especially muntjac, through appropriate fencing to reduce browsing of honeysuckle may be beneficial in some woodlands. Conifer Plantations can retain abundant honeysuckle along semi-shaded ride margins. Thinning of conifer plantations can create suitable dappled shade providing honeysuckle is not excessively damaged or removed during timber felling and extraction.

Rides

Rotational cutting of clearings and rides is most beneficial as it adds variety to the vegetation structure. The length of rotation will be dependent on the individual site but can be anything from 3 to 12 years. Cutting in autumn and winter months is preferable and ride edges should be managed alternately in consecutive years if practical. Rides which are one and a half times as wide as the height of the bordering trees and of east-west orientation are the sunniest and most suitable for this species.

Glades

A range of vegetation structures should be encouraged within glades with a shorter flower-rich central zone, a zone of taller herbs and grasses and a scrub margin adjacent to the mature trees. Scallops and box junctions can also be created to provide more open habitat encouraging some controlled growth of flowering bramble. Scallops are effective to increase the length of ride edge habitat and to provide warmer sunlit and wind sheltered zones. Management by cutting back should be planned in sections to avoid disrupting large areas in a single clearance operation.

Phenology

Ova - July to August

Larva  -  August to May

Pupa  - June (September if there is a second brood)

Adult  - June to August (September to October for second brood)

Threats to white admiral butterflies

• Butterflies are dependent on specific food plants. In this case of the white admiral butterfly there is only one food plant which is native honeysuckle Lonicera periclymenum. Quite simply, if this plant is absent from a habitat, the butterfly cannot survive there.
• An over-tidied woodland is not good for this butterfly as this usually results in the removal of suitable honeysuckle strands.
• Woodlands that are not managed at all will quickly lose any clear glades, rides and woodland edge habitat where honeysuckle can thrive.
• Fragmentation of woodlands can separate established colonies if these become too small but the power of the species to spread by flight should overcome this difficulty provided larval food plant can be found
• Timber extraction from woodlands can destroy a colony if there is an insufficient quantity of food plant left undisturbed over the winter period while larvae are hibernating or if the larvae are inadvertently removed during wood extraction.
• Climate change can threaten this butterfly as weather patterns become more extreme with extended cold periods of summer being particularly destructive to the survival of larvae.

Conservation status

• Butterfly onservation priority: High
• Section 41 species of principal importance under the NERC Act in England
• UK BAP status: Priority Species
• London BAP status: Priority Species
• Priority Species under the UK Post-2010 Biodiversity Framework

Actions

References

Asher, J., Warren, M., Fox, R., Harding, P. British Butterfly Conservation Society, Biological Records Centre (Institute Of Terrestrial Ecology and Dublin Naturalists’ Field Club (2001). The millennium atlas of butterflies in Britain and Ireland. Oxford ; New York: Oxford University Press. (pp 185-187).

Butterfly-conservation.org