spring

©P.Eeles

R.J. Curtis & I.M.D. Maclean

Marsh Fritillary on the Lizard

The Marsh Fritillary (Euphydryas aurinia)

The Marsh Fritillary is one of our most attractive and rarest butterflies. They are characteristic

of damp grasslands and more brightly patterned than other Fritillaries, with wings chequered

orange, cream and black.

It was once widespread in Britain

and Ireland but has declined

severely over the last century – it

is now one of the most rapidly

declining butterfly species in

Europe, and fully protected under

European and British legislation.

The principle reason for the

decline is because many of the

wet meadow habitats have been

drained for agriculture, although

scrub encroachment through lack

of management and climate

change are also potential factors.

A Stronghold in the Southwest

In England, the Marsh Fritillary is predominantly

restricted to the wetter, south-western counties.

There are probably only a dozen or so colonies in

Cornwall. Although some large populations

remain around Bodmin Moor, many colonies are

very small supporting only tens of adults.

Recently, Marsh Fritillaries have probably become

extinct in West Penwith, and populations have

plummeted around former stronghold sites (e.g.

Goss Moor). There are approximately a handful of

colonies on the Lizard, although several sites

support quite large populations.

This leaflet provides information about the Marsh

Fritillary on the Lizard, and how to ensure that

they remain a feature of the Cornish landscape.

©P.Eeles

© Data copyright Butterfly Conservation 2016

Life Cycle

Adult butterflies normally

emerge during May, although the

date varies depending on the

warmth of the spring. Like most

butterflies, there has been a

noticeable advance in emergence

dates with climate warming.

Males emerge first, and patrol

their territories with low zig -

zagging flights while searching for

freshly emerged females with

which to mate.

Females are noticeably bigger although slightly paler than

males, and most conspicuous when gravid with eggs – she

carries so many that she is barely able to fly. She searches

for suitable Devil’s-bit Scabious plants and lays her eggs in

batches on the underside of the leaves.

The eggs hatch after a few weeks and the gregarious

larvae spin a protective web around the scabious on

which to bask and feed communally. Although they have

few predators, they are attacked by a parasitic wasp

which can cause high larval mortality. In autumn the

larvae spin a hibernaculum with much denser silk which

insulates and protects the caterpillars during the winter.

Indeed, on wet sites they can even survive being

submerged for several weeks.

They re-emerge early the following spring (late February / early March) and the webs and

larvae become very conspicuous against the low winter vegetation. After several weeks the

larvae become solitary and disperse widely. Pupae are formed in low vegetation and adults

emerge a few weeks later.

©P.Eeles

©D. Batchelor

Research on the Lizard

The University of Exeter is currently conducting research on Marsh Fritillaries on the Lizard

with three primary aims:

To identify the locations of all remaining colonies, and to estimate population size.

To understand the determinants of distribution and abundance at these colonies - why

do they occur where they do?

To use this research to conserve remaining populations, and to inform landowners how

best to manage these sites to

maximise population levels.

Population size is calculated by

counting the number of larval webs

during February and March, when

the post diapause larvae are most

conspicuous. In 2016 all potentially

suitable sites were surveyed for

larval webs, but no more than a

handful of colonies were discovered,

and several of these were quite

small.

Research has shown that Marsh

Fritillaries have distinct habitat

preferences. Most importantly seems

to be the availability of the sole

hostplant, Devil’s-bit Scabious. The

large numbers of communal larvae

quickly devour the plant on which the

eggs were laid, and so often have to

travel relatively large distances to find

food. This problem is exacerbated in

the following spring when the larvae

undergo continued bouts of feeding to

sustain several weeks of rapid growth

– starvation is a frequent cause of

mortality.

Secondly, this butterfly shows a preference for unfertilised grassland habitats which have an

intermediate turf height ranging from 5 – 25cm tall, so both tightly grazed and unmanaged sites

are rarely occupied. Thus there is a danger associated with both over and under managing

Marsh Fritillary sites.

©C. Lumsden

©J. Bacon

Conservation

The Marsh Fritillary is one of the most seriously threatened butterfly species in the U.K.

Wide-scale habitat destruction and degradation of unfertilised grasslands now means that

most Marsh Fritillary colonies exist as metapopulations (separate populations connected

through dispersal). However, females are generally poor dispersers, colonising sites further

and further away only as their egg load lightens. Furthermore, as an occupier of mid

successional habitats many colonies are also ephemeral, utilising sites containing early

successional vegetation and vacating them when they become overgrown. Therefore its

continued survival is reliant on maintaining and improving a close-knit network of low

intensity livestock farmed sites across the landscape.

Previous research undertaken by Butterfly Conservation across England has shown that:

90% of occupied sites contain locally abundant Devil’s-bit Scabious. However, height

and structure of vegetation is extremely important, with larvae often found at the

boundary between long and short vegetation. Creation of a mosaic sward is thus a

paramount management objective.

Overgrazing caused a decline in 37% of sites, with the best sites using cattle (0.1 –

0.4 livestock units / hectare / year) of approximately one suckler cow per hectare for

3 months of the year. Ponies are also suitable, but sheep create a tight sward which

prevents scabious plants from germinating and so are generally unsuitable.

Too little or no management caused extinction on 35% of sites. Both coarse grasses

and scrub shade out Devil’s-bit Scabious. Therefore, scrub cover should be kept at 5

– 10% (although a higher amount on high or exposed sites is fine), cut and removed

between October – March, and ideally managed on rotation.

Mowing is generally unsuitable (prevents a mosaic structure of vegetation), although

small scale burning in early spring can be beneficial, especially if combined with

grazing. However, large scale burning is likely to destroy colonies.

Climate change is potentially a threat to this species, as warmer temperatures could

mean damp habitats could become progressively drier, and vegetation growth rates

increase expediting the dominance of coarser grasses and scrub.

The recommended management of creating a mosaic vegetation structure can

ameliorate the impact of climate change and is beneficial to many other species

which inhabit grassland habitats.

©G. Richardson ©P.Eeles ©P.Eeles

The Importance of Habitat Structure.

Like many butterflies, the key to conserving populations of Marsh Fritillaries relies on

maintaining suitable habitat quality for the larvae. This is the longest and most vulnerable

stage of the life cycle and larval survival is therefore reliant on the amount of Devil’s–bit

Scabious and the structure of habitat that surrounds them.

Habitat structure is important as the larvae need to raise their body temperature to

approximately 35 degrees Celsius to maximise the efficiency of a gut enzyme in order to

digest their food. Larvae thus require small patches of taller vegetation which can support

the construction of a silken web which the larvae use to bask communally, thus raising their

body temperature more effectively within a group compared to individually. These basking

platforms are created with a southerly aspect, and the black larvae align themselves in neat

rows to maximise the warmth of the weak, early spring sunshine. Once their food is

digested they move off the webs and resume feeding. By March and April the larvae moult

into their fifth and sixth instars which have a row of highly reflective silver spots along the

length of their bodies. This allows larvae to reflect as well as absorb heat, and with the

warmer spring sunshine they can now self-regulate their own body temperatures so

communal basking is unnecessary and the larvae become solitary.

Creating a structurally diverse habitat within sites is therefore an important factor in

managing Marsh Fritillary colonies.

Basking Marsh Fritillary larvae as seen through the lens of a thermal camera. Note an

individual larvae at the front of the group is starting to move away to resume feeding.

©R.Curtis

Fire as a management tool.

Used correctly, the use of fire can significantly enhance site condition for the benefit of

Marsh Fritillaries. However, misuse and extensive burning can be severely detrimental and is

frequently responsible for local extinction of small populations.

Marsh Fritillaries are in the larval stage from June – April. The most important factor is

therefore to burn CLOSE TO, NOT ON areas of habitat where they occur (e.g. at least 30

meters or so away). Historically there are numerous examples of the inappropriate use of

fire causing local extinctions by burning too close to colonies.

Ideally, several small areas should be burnt (e.g. ideally from 50 - 1000m2), thus creating a

patchwork of heterogeneously diverse habitats, essentially providing areas for egg-laying,

roosting and feeding (nectar plants) all within close proximity.

Areas should be burnt on rotation (every few years) to allow time for Devil’s-bit Scabious

to grow (female Marsh Fritillaries select plants for egg-laying on the basis of prominence and

number of leaves).

There is evidence to suggest that a rapid burn with the wind will cause less damage to

Devil’s-bit Scabious plants, reducing the time for this newly burnt area to become suitable

for egg-laying.

Burning should generally occur during January and February, and fire breaks should be

utilised to ensure only the designated area is burnt.

Finally, if land you intend to burn contains Devil’s-bit Scabious and you are unsure whether

Marsh Fritillaries are present, please contact us prior to burning and we will be happy to

advise regarding specific habitat management for your site.

Fire can be beneficial for Marsh Fritillary populations, but care is needed to prevent local extinctions.

©A. Nichols

From research to practical conservation: Grazing exclusion zones

at Predannack.

There is strong evidence to suggest that the size of many butterfly populations is directly

related to the amount of larval foodplant present within a site.

Researchers at the University of Exeter in collaboration with Natural England, the National

Trust and local landowners have established grazing exclusion areas at Predannack.

Currently there are two zones, one on Natural England managed land to assess whether

allowing Devil’s-bit Scabious to develop into larger, more prominent plants will increase

numbers of Marsh Fritillaries, with the additional benefit of preventing trampling of larval

webs during early spring. The other exclusion zone is on adjacent National Trust land with

the aim of encouraging Marsh Fritillaries to colonise this area.

Both these sites will be closely monitored to further increase our knowledge to understand

the optimum stocking levels to maintain and enhance Marsh Fritillaries at Predannack.

The establishment of grazing exclusion zones at Predannack to assess the impact of stocking

levels on Marsh Fritillary populations.

©A. Nichols

Seeing Marsh Fritillaries on The Lizard: Predannack Head

Drive to Lower Predannack

Wollas Farm and park in the

National Trust Car park. Take

the path to the right leading to

the coast. Cross the stile. Join

the coastal path by walking

down the stone steps. On the

coastal path turn right, heading

north, through the wooden

gate and keep walking until you

reach a stone stile. The suitable

Marsh Fritillary habitat begins

after the stone stile on Natural

England managed land.

The grass is short on this site and Devil’s-bit Scabious

plants are widespread but small. The best time to see

adults is during late May and early June. Please take care

to avoid treading on larvae if visiting in February and

March.

©C. Lumsden

© Crown Copyright/database right 2016. An Ordnance Survey/EDINA supplied service.

Acknowledgements

We would like to thank Natural England, particularly Jeremy Clitherow, Philip Bowler and Steve Townsend,

the National Trust, particularly Justin Whitehouse and Rachel Holder, Nick Marriot at the Cornwall Wildlife

Trust and Jenny Plackett at Butterfly Conservation. We would also like to thank the photographers for

permission to use their stunning images.

Please contact Robin Curtis r.curtis@exeter.ac.uk for further information or management advice.

How you can help…

Report any sightings of Marsh Fritillary (adults but particularly larval webs) to the local

butterfly recorder (cbcrecords@cornwall-butterfly-conservation.org.uk) or to The

Environmental Record Centre for Cornwall and the Isles of Scilly (ERCCIS)

http://www.erccis.org.uk/wildlife_recording/submit_records_online. Records of timed adult

or larval counts (even 5 minutes) are especially useful.

While walking around the Lizard in February and March watch where you put your feet –

while it is unlikely that trampling has a major effect on population size, a misplaced foot can

destroy an entire larval web and many well walked paths go through Marsh Fritillary

colonies….

Appreciate this butterfly as a special addition to the Cornish landscape and encourage

others to see and value it.

©W. Langdon