Marsh Fritillary reintroduction in Cumbria

THE MARSH FRITILLARY IN CUMBRIA

This stunningly beautiful butterfly was just managing to hang on at one or two colonies in the Lakeland area (the only Marsh Fritillary sites between Anglesey in Wales and Islay in Scotland) but by 2005 none were reported, suggesting it had become extinct.
After the Second World War there were over 200 colonies in north Cumbria from Ennerdale to Penrith. Colonies from the Solway Mosses, Ennerdale and Eskdale have long since gone. The butterfly was once abundant just 3 km west of Carlisle in the meadows around Orton Woods and a few km further west at Finglandrigg Wood.
The remaining colonies were so isolated that efforts to improve the habitat had no beneficial effect because there was no mixing between colonies and in-breeding led to low fertility and weak specimens.
Fortunately in 2004 it was realised that the last remaining colony was under threat (there were only two larval webs) and 168 larvae were removed under licence for captive breeding.
A further 80 larvae were added to these under licence from several strong colonies in Argyll, Scotland; tests showed these were most genetically similar to the Cumbrian race.
Trials were undertaken with breeding solely from the Cumbrian specimens and with mixed breeding of Cumbrian/Scottish stock. Those solely of Cumbrian origin did not survive but the others formed the basis of a strong breeding programme in subsequent years.
After successive years of breeding, by early 2007 around 40,000 larvae were held in captivity. In March of that year some 37,000 were released back to four prepared sites, again under licence. The largest number were released at a central Lakes site, with others on the Solway, in West Cumbria and near Penrith. Once the right management is in place Devil's-bit Scabious can be planted; on one occasion a donation enabled 2500 plants to be purchased and planted. This is the first time captive breeding and release on this scale has ever been attempted with butterflies.
The change from ugly caterpilar to beautiful butterfly takes just over three weeks and is one of the wonders of nature (see photos above and below).
All but one of the sites in Cumbria are on private land. The only accessible site is Finglandrigg NNR between Kirkbampton and Kirkbride on the Solway Plain. This wardened site is being used to provide an opportunity for members of the public to see this terrific species. At the car park (map ref NY 283572) follow the butterfly trail about a mile through the wood until you come to an open area through a gate with a sign on it saying 'you've finally made it, this is the site'!
In 2007 there were very encouraging signs that the release programme was working well, except at the Penrith site where conditions are still not ideal. Good numbers of adults were seen during the flight season and larval webs found from mid-August onwards. These sites have been self-sufficient and with increasing numbers of larval webs through 2008, 2009 and 2010. Adults emerged at one site in 2010 despite having been submerged for days under three feet of water following the huge floods of the previous winter in the Keswick/Cockermouth area. A further 20,000 larvae were released at two further sites in Ennerdale in 2010.
In 2011 the plan will be to release 8000 larvae on two new sites near the existing Ennerdale sites, thereby extending the corridor of occupied sites down the length of the valley (see photo). These new sites have been prepared by management and the planting of hundreds of Devil's-bit Scabious plants. This will bring the total number of larvae raised and released in Cumbria to around an incredible 70,000.
Massive declines in populations throughout Europe make this the only butterfly in the U.K. to gain protection under the E.U. Habitats and Species Directive.
Colonies do undergo huge fluctuations in size over the years, but it is the disappearance of colonies that is worrying.
The Orton Wood colony was studied for 55 years. Between 1881 and 1894 it increased from common to very abundant, before declining over the next ten years, then becoming scarce between 1906 and 1912 and very rare between 1913 and 1919. Numbers increased steadily between 1920 and 1925 and by 1935 it was described as excessively common. Sadly this colony became extinct.
The Marsh Fritillary is predominantly a species of damp unimproved grassland on the western side of Britain; its food plant is Devil's-bit Scabious (although it will use Honeysuckle when pressed). The peak flight time in Cumbria is usually the first two or three weeks of June.
The 'improvement' of old pasture for intensive agriculture leads to the eradication of the foodplant. Colonies become fragmented and the species cannot survive population crashes by recolonisation from neighbouring colonies nor can genetic reinforcement occur by mixing of populations.
The larvae need direct sunlight - they like to bask in the warmth as an aid to digestion (don't we all!).
Bad, particularly wet, weather at critical times (and for several years in succession) affects the success of the species. Numbers can be reduced by a parasitic wasp, which injects its eggs into the larvae so that they are eaten from within, but this does not seem to be a major problem in Cumbria at present!
Recolonisation depends on the presence of adjacent colonies; females will wander several kilometres, especially towards the end of their flight period (when the weight of eggs carried is reduced).
The Ministry of Defence look after possibly the largest colony in Europe - in 1999 it was estimated that 10,000 larval webs were present on the Salisbury Plain Training Area. Nice to know our taxes are being put to good use!!

PHOTO GALLERY OF THE LIFE CYCLE

The gorgeous pupa on the left is attached to a leaf of Devil's-bit Scabious. A couple of days after the caterpillar attaches, the black skin of the caterpillar splits from the bottom and rolls back as the pupa twitches and flicks to try to shake it off (it only takes about 30 seconds). Sometimes, as on the left, the old skin remains attached at the top. The photo on the right shows the markings on the part of the pupal case within which the wings will develop.

The pupal stage takes 16 - 19 days (but can take up to 30 days if the weather is very cold) during which hormonal changes occur that make human puberty look a doddle! The adult emerges with wings tightly folded; these must be pumped up over the next half hour, then allowed to dry.

Female adults are generally larger than males with bolder markings; males look darker when fresh.
(the male is on the right in the left-hand image). However, size varies enormously in this species; body shape (fatter and more rounded in females) is the best guide to identify the sex.
On the right is a roosting adult showing the underwing pattern; note the gorgeous ginger top-knot of a freshly emerged specimen.

Marsh Fritillaries are not avid feeders as adults, but sites do need to have suitable nectaring flowers, especially if poor weather interrupts the mating and egg-laying processes. Members of the Daisy family and the Spotted and Marsh Orchids are typically in bloom in Cumbria during the flight period of late May into June.

Successful breeding depends on the weather. Here intense heat and dryness, just before emergence from the pupa when the wings are forming, probably affected this female. Pupae can fail completely in very cold weather.

A mating pair - a rather small and less bright female above. Mating usually starts around noon and can last through the afternoon. A high proportion remain coupled overnight - not always with wings neatly interlocked as here!

Laid Back! Egg laying with crossed legs. Most egg laying occurs in the early afternoon. This position may be held for three or even four hours if the weather holds. The eggs are laid on the underside, often two or three deep, a body's length in from the edge of the leaf. The leaf chosen is normally on the side of the plant receiving afternoon sun.
If the weather is very hot the wings may be held closed during laying as on the right.

Eggsactly four weeks later.... on the left, just hatched and taken their first nibble. Again, very cold weather can delay hatching by two or three weeks. Length of each caterpillar 0.5 mm approx.! On the right, two days later..twice as long. At this stage the larva find protection from the elements on the underside of the leaf.

Remarkably, just ten days after hatching, the tiny larvae, no more than 2 mm long, spin a web. This offers them greater protection from the weather.

Communal living! About four weeks later the larvae form a seething mass, basking in the sun. The oldest are now recognisable as spiky caterpillars about 6 or 7 mm long!

Feeding front! After around six to seven weeks the larvae are almost 1 cm long and very hungry.

Going....gone! Finally, as August ends, they prepare to hibernate for the winter.

Look at me now! Around the last week of February they emerge from hibernation transformed and seek warm basking spots.

For the first month after emerging for the spring the larvae appear to eat very little (in the wild the Scabious would not be producing new growth). They spend most of their time basking, appearing to gain their energy from the sun. Then, about one month after emerging they undergo the next moult, becoming the fifth instar - old skins remain attached to the substrate (see left). They now eat voraciously (Devil-s-bit Scabious or Honeysuckle), between bouts of basking in the sun, and grow at an enormous rate. The three weeks from the end of March are the main growth period in the larval stage - wet weather at this stage can hold them back.

After about three weeks as 5th instars they undergo the final moult into the 6th instar - note the yellow-head and white-tipped spines just as they have shed the skin and become the sixth instar. They now complete their growth quickly (middle photo) and cover a lot of ground on the look out for pupation sites.

However, for reasons that are not yet clear, about 5% of the larvae seem to get left behind and are still very much smaller at this time (photo right).

All packed up and ready to go on their holidays - Ennerdale here we come! The release programme aims to put the captive larvae back in their natural habitat a few days before pupation, thereby minimising losses by predation (Field Voles take them but not Wood mice).