Marsh Fritillary explosion in Lincolnshire

[petesmith]

This year's Marsh Fritillary population explosion in central Lincolnshire continues to astonish and amaze us! With many thousands of butterflies on the wing in an area of just 4 hectares, the air is literally shimmering with these gorgeous insects. It is hard to get a handle on the exact number of butterflies present, but today I took a slow stroll around both meadow areas, and in the space of 35 minutes I counted a staggering 477 mating pairs. Tails of ten, fifteen or twenty males could be seen pursuing single females, and in amongst the vast numbers, a few aberrant forms could be found. My favourite one is the first one below, two photo's of the same individual (unfortunately it had lost an antenna):

Here is another slightly aberrant individual, again, two shots:

And this one is also quite dramatic:

Below is a particularly red example, slightly deformed:

One of the 477 mating pairs:

A trio at nectar:

And a short bit of video of a few at nectar on hawthorn blossom can be seen at the following link https://www.youtube.com/watch?v=x9XnfzqYbaA

If anyone has any ideas for names for any of the above aberrations I would be very interested to hear from you!

[selbypaul]

Wow, what incredible numbers! What has caused such an explosion in numbers? Was it weather conditions last summer?

[David M]

Wow! 'Explosion' is the right word for it, Pete. These are staggering statistics and some of the aberrations are remarkable.

I've read about historic instances such as this. It'll be interesting to see if other parts of the UK see similar numbers.

[petesmith]

Wow, what incredible numbers! What has caused such an explosion in numbers? Was it weather conditions last summer?

Paul, it is hard to be sure, but seems likely that climatic factors have played a big part in triggering this. The population has waxed and waned at this site over the past 25 years, but has been building exponentially for the past three seasons. Last year's emergence was remarkable, but this year it has gone through the roof!
There has been little if any change in management at the site, which receives an annual cut during the winter.

The main concern now is that we are heading for a huge population crash - many larvae exited the meadows this spring and wandered off into the surrounding woodland in search of food, as the Devil's-bit Scabious was razed to the ground by the teeming masses of caterpillars. Unfortunately, this colony is surrounded by a sea of agriculture, and there is nowhere else for the butterfly to colonise - no metapopulation structure exists, so no extinction/colonisation pattern can really occur locally.

Hopefully, enough will survive to ensure continuity, but local extinction next year must now be a distinct possibility...

[petesmith]

Wow! 'Explosion' is the right word for it, Pete. These are staggering statistics and some of the aberrations are remarkable.

I've read about historic instances such as this. It'll be interesting to see if other parts of the UK see similar numbers.

David - indeed, I too have read of such occurrences where populations undergo extreme increases in numbers, but I never expected to witness such events myself! I feel like I have time-travelled back into the Victorian era. It is hard to put into words the sensation and emotion of being stood in amongst such phenomenal numbers of such a beautiful and threatened species as this...

[Chris Jackson]

An interesting report, Pete, particularly when I think that this is not a particularly protected species in France (as far a I know, and apart from some subspecies).
We clearly have less problems with land occupation with less pressure on the BF and its host plant.
Chris

[PhilBJohnson]

Hello Pete,
By May 20th, some Marsh Fritillary butterflies had dispersed as far as the meadow to the rear of the butterfly garden. A last one was seen heading in the direction of Snake Holme Pit! (not my interference).
When there are lots of them, they fight a bit in hot weather and fly further to colonise different areas.
I also read on UK Butterflies that some caterpillars could wonder into hedgerows and eat honeysuckle, if Devil's-bit Scabious (DBS) was in short supply.
It was kind of strange to think that the adult Marsh fritillary butterflies will not see a DBS flower to nectar on, as they appear much later in summer in the UK.
DBS is an important nectar source for butterflies also. In Sweden where butterfly flight seasons are relatively compressed due to climate. Scabious flowers during Small Pearl-bordered, Pearl-bordered, Dark Green and Silver-washed Fritillary flight times and they love it. I am convinced we need to bring back those plants in our countryside to insure a better Fritillary future.

If anyone has any ideas for names for any of the above aberrations I would be very interested to hear from you!

I am not sure Pete, but I think I will call "my" Marsh Fritillary "Joyce!"

"Joyce"

[CallumMac]

I remember thinking during last year's visit to CFW that it would be a once-in-a-lifetime experience to stand amongst such high densities of Marshies. Incredible to see that the numbers have grown even further. And very encouraging (for the long-term persistence of the species in Lincs) that there are now emigrant individuals popping up in other local reserves - not just Phil's Snakeholme sighting, but also reported from Red Hill on Tuesday.

I will try to get down there this weekend to soak it all up again!

[Roger Gibbons]

Hi Pete,

477 mating pairs! Are you sure you didn’t double count, there may only have been 476...

I have tried to find words to describe such a scene but the English language doesn’t have the necessary superlatives.

It is an amazing species with so many forms – from the UK form to the orange form provincialis (which is the norm here in Var as Chris has shown) to the high altitude debilis, to the high altitude dark from glaciegenita. It seems to be able to adapt to so many highly varied terrains that its English name of “Marsh" seems very limited.

Provincialis emerges, often in great numbers in the far south of France, maybe up to 100 countable in a short stretch of open track. And, if you're lucky, even a mating pair or two.

Quite why “Marsh" should be so variable and able to occur in such vast numbers is a mystery when its four French Euphydryas cousins – none of which occur in the UK – are so rare and limited, is a mystery. It is a fabulous group – Scarce Fritillary, Cynthia's, Asian and Spanish.

Roger

[petesmith]

I will try to get down there this weekend to soak it all up again!

It is well worth a visit CallumMac!

Hello Pete,
By May 20th, some Marsh Fritillary butterflies had dispersed as far as the meadow to the rear of the butterfly garden. A last one was seen heading in the direction of Snake Holme Pit! (not my interference).

Phil - they are indeed attempting to move away from the core area - I saw a stray individual flying around the Western edge of College Wood last week. Shame there is virtually no suitable habitat nearby for them to colonise...

Hi Pete,

477 mating pairs! Are you sure you didn’t double count, there may only have been 476...

I have tried to find words to describe such a scene but the English language doesn’t have the necessary superlatives.

It is a fabulous group – Scarce Fritillary, Cynthia's, Asian and Spanish.

Roger

Roger - it may be necessary to invent some new adjectives to describe the experience! They are a fabulous butterfly, as are others in the group. Cynthia's, Asian and Scarce Fritillaries rank very close to the top of my favourite European species. I have yet to have the pleasure of meeting up with desfontainii, but hope to see it one day!

[False Apollo]

I witnessed a Marsh Fritillary population explosion near Christchurch, Dorset where numbers literally went through the roof a few years ago. Indeed there were so many you had to be very careful where you put your feet as they were everywhere. They were even turning up in nearby gardens! Had one extreme aberration which interestingly had a damaged antennae. There were so many that some were found along the road into Christchurch having been hit by cars as they dispersed. The next year numbers plummeted, and they never recovered. The colony no longer exists. I know many larvae were parasitized and possibly there was not enough Devil's Bit Scabious to feed the next generation. It seems that big numbers do not necessarily mean big numbers will occur the next year. Most colonies near me are at numbers of 20-40 (from reports). One famous Dorset colony near me has done really badly, possibly due to overgrazing, I did not see any there last year. I will be interested to see how colonies are doing this year compared to last year locally.

[jasonsargerson]

Looking on the Lincolnshire sightings record, 2018 and 2017 were good years for the Marsh Fritillary at Chambers Farm.

So three good years in a row, hopefully there will not be a population crash.

I visited on 15th May - see my personal diary for more photos and a video clip.

[KeithS]

Is it worth maybe redistributing some of the resultant eggs and larvae from this superabundance to other areas where the food plant can be found but the butterfly is absent?

[PhilBJohnson]

Is it worth maybe redistributing some of the resultant eggs and larvae from this superabundance to other areas where the food plant can be found but the butterfly is absent?

"Please remember that this species was "fully protected" under UK law, although excess butterflies without larval food plants might have been considered by someone as wasted"
DBS Check
"More-mature larvae tend to feed alone and are often found wandering across open ground looking for their next meal or, eventually, a pupation site. If there is a shortage of foodplant, the larva is known to feed on alternative food sources, such as Honeysuckle growing in hedgerows" Reference: UK Butterflies -Marsh Fritillary-Larva
Spring Caterpillars
On April 16th 2019, people walking on the white marker post route that is adjacent to the meadow, reported seeing many black caterpillars crossing the path and were finding it hard to avoid them.
How super-abundance of MF might affect the larval food plant.
I thought that in Lincolnshire there could be whole arable fields devoted to growing Devil's-bit Scabious (DBS), sponsored by someone or devoted by "market force". Cornflowers were grown like that for aesthetic appeal for someone, somewhere.
The SSSI Little Scrubs Meadow (Forestry Commission) was thought to have been cut once a year in late summer as a management plan.
I thought that people a little more unfamiliar with Devil's-bit Scabious could identify it more easily in a survey, when it flowered, just before a meadow was cut. Ragged Robin might be a plant more easily seen in the next week or two because of it flowering.

Outside the Education Centre at Chambers Farm Wood on May 20th 2019

Kind Regards

[petesmith]

Is it worth maybe redistributing some of the resultant eggs and larvae from this superabundance to other areas where the food plant can be found but the butterfly is absent?

KeithS - in my opinion, yes, absolutely, I agree that this would be a sensible course of action, to help to conserve this rare butterfly at a site where it has been present for over 25 years. The re-distribution of a large number of eggs/larvae would both take the pressure off the relatively small area of currently occupied habitat, which may well be completely overwhelmed by the potential number of offspring this year, whilst also providing the opportunity to create some (possibly short-term) peripheral colonies nearby, which could act as recolonising sites for the main meadow habitat.

Unfortunately, this will be a contentious subject amongst many members of the butterfly community, where opinion is polarised both for and against intervention such as this, and related issues of the collection/release/introduction/re-introduction of butterflies.

I suppose the first thing to consider is the legal situation. With the Marsh Fritillary being fully protected under schedule 5 of the 1981 Wildlife and Countryside Act, and at this particular site occurring on a site designated as a SSSI, then a license from Natural England would be required prior to the removal of any stock. Having worked for 15 years alongside Natural England (formerly English Nature), Forest Enterprise, Lincolnshire Wildlife Trust etc as a part of the Bardney Limewoods NNR Advisory Committee in the late 1990's and 2000's, I think it would be highly unlikely that they would approve such a license. Sadly, the fortunes of Marsh Fritillary at this site were always secondary to the main raison d'etre of the reserve, namely maintaining the floristic diversity of the site at whatever cost to the entomological interest.

Fortunately the butterfly appears to be spreading out of its own accord into the few nearby habitats capable of supporting it within the Chambers Farm Wood complex of rides and meadows. It has also been seen several miles away, attempting to find non-existent habitat in the surrounding arable countryside.

Whilst enjoying the spectacular phenomenon of this year's "hyper-auriniastic" experience, we can only hope that the species will somehow find a natural balance and manage to maintain its presence for many years to come!

[KeithS]

My own experiences with bodies such Natural England and Plantlife suggests that the outcome depends upon who you talk to. NE can be pretty reasonable if you can meet someone in the field and talk directly to them before applying for a licence.

In this case it seems ridiculous to run the risk of losing both the Marshies and the Devil’s Bit Scabihous (not a common plant by any means) if a superabundance of MF larvae completely strip the foodplant foliage or prevent it from setting seed.

Common sense would suggest a little intervention would be in order, but there may well be much more complex and interactive factors at work here.

I suspect a superabundance of any type of butterfly makes for an equal boom of associated parasites and predators, one that may well adversely impact upon other species.

There are those who feel the “nature should be left to find its own balance”, even though human activities have skewed that balance for many years. Personally, I think that this “balance” has to be actively managed these days. Otherwise, we have the ironic spectacle of worthy conservationists bemoaning (say) the lack of birdsong in the woods, when the same woods are full of aggressive and clever magpies, greedy wood pigeons and omnivorous grey squirrels....

[CallumMac]

Personally, I think that this “balance” has to be actively managed these days.

The Knepp Wildland project is a pretty spectacular example of what can arise when Nature is given the space to manage itself. My own (also personal) view is that certain sectors of society have been far too keen to promote an agenda of actively managing nature's "balance" over a timescale longer than my lifetime. Those same sectors of society are perfectly happy to throw that same balance out of kilter by releasing millions of reared pheasants and partridges every year...

On which note, I have the uneasy feeling, having visited yesterday to see for myself, that Chambers Farm Wood is also a good example of what can happen when humans interfere in natural processes. Clearly the Marshies "arrived", somehow, in central Lincolnshire, and their parasitoids didn't. With no natural enemies to keep their numbers in check, a foodplant shortage could been seen as an inevitable conclusion. Let's hope that enough caterpillars survive next spring for the population to avoid extinction...

[PhilBJohnson]

New Population of Marsh Fritillary (MF) in nearby Southrey Wood, Lincolnshire.

One might be interested to know. Plenty of Devil’s-bit Scabious (DBS) on central rides near the tower. Here are some of my pictures from today. My Wife and I saw between 6 and 12 MF during the time the Butterfly Conservation work party was scheduled.

Marsh Fritillary, Southrey Wood, Lincolnshire

DBS Check, MF and locational tower in the background.

My Wife dressed for Work