The earlier pictures were taken on my wee compact Canon ixus 970IS, which involved sneaking up on the butterflies. This can be very frustrating when they fly off, but very rewarding when they don't!

Since 2012 I have been using a Panasonic Lumix FZ150, which allows me to zoom in to the butterflies from a couple of metres away.



Friday, 9 February 2018

The Fall and Rise of the Wall Brown

While I was delighted to see the arrival of the Wall Brown, Lasiommata megera, in 2010 and its subsequent spread across East Lothian I note that it has declined severely in Southern England. Strangely, it is hanging on around the coast of England, but since the mid-1980s, what was once a very common butterfly has become a rare sight in an area centred around Buckinghamshire and Oxfordshire.

The Wall Brown normally produces two generations of butterflies a year. The first generation emerges in May and June and a second generation occurs in August and September. This species over-winters as a caterpillar.

A study, published in December 2014, The lost generation hypothesis: could climate change drive ectotherms into a developmental trap? By Hans Van Dyck, Dries Bonte, Rik Puls, Karl Gotthard and Dirk Maes looked at the declining number of Wall Browns in Belgium.

Their theory is that due to climate change the season for this butterfly is extending. If the first generation is emerging earlier and the subsequent generation is therefore appearing earlier then there is a potential for a third generation to emerge late in the season. However, there is not enough time for this third generation to breed, or for their eggs to hatch in time to make it through the winter. Presumably, eggs and chrysalises can’t survive frosts. It would be interesting to know if all instars of the caterpillar can survive cold weather.

This theory sounds very plausible to me and it could also help to explain why the Wall Brown is now spreading north into East Lothian. We have certainly been experiencing less severe winter weather here over the last 20 years. Possibly before that our season wasn’t long enough for two complete generations to survive and go on to produce caterpillars before the winter set in. In effect we are now experiencing the sort of weather that was once more common in the Home Counties.

Number of Wall Brown records received over the last five years
2013
2014
2015
2016
2017
54
78
70
129
273

2017 was the best year we have had for Wall Browns. The number of records I have received has increased each year since they were first recorded in East Lothian in 2010. Last year we recorded more than twice as many Wall Browns as we had in 2016. They have now made their way right around the coast and to various inland sites.

They are a very welcome addition to the butterflies of East Lothian.

25 comments:

  1. A very pretty thing that I think most of us overlook.

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    1. I think you are right Michelle. Most people don't even notice that they are there!

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  2. Interesantísimo trabajo, Nick. Las mariposas son los agentes más importantes para detectar la calidad ambiental, si el mundo va mal ellas son las primeras en detectarlo... Un fuerte abrazo desde Asturias.

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    1. Gracias Belen. ¿Has notado algún cambio en las mariposas de Asturia?

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    2. Nick, la pasada temporada ha sido muy rara e inusual. Esperemos que esta, con las grandes nevadas que ha habido, sea mucho más satisfactoria. Me apunté a un recorrido BMS en el Parque Natural de Ponga, ya te iré contando. Un fuerte abrazo.

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    3. Belén,
      Sí, espero que un invierno frío conduzca a un buen verano. Espero escuchar acerca de su recorrido de BMS.

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  3. Saw a few in Norfolk this year, when I was a kid in the 60's they were very common.

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    1. I believe they are still holding on around the coast. Maybe the winter weather is less severe there. I would be really interested to see where they occurred in the 1700s. Many butterflies that have moved into East Lothian in recent years occurred here in the 1700s before there was a dip in temperatures.

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  4. It’s colors are close to golden with the light on the sun. It is beautiful. I hope climate change doesn’t harm them in any way. How long do they live in their flying stage? The Caribbean Monarch barely lives 3-5 days.

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    1. Hi Maria, they probably live for about two weeks. I think it will depend on the weather. If there are a few cold, wet days and the butterfly can find shelter then it may live a little longer. Because some species hibernate over here, it is possible for butterflies such as the Peacock to live for nine months!

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  5. Hello Nick,
    Your post is very interesting and I believe it doesn't concern butterflies exclusively. Knowing birds quite well, I I am convinced it applies to them too.
    The climate in Johannesburg was fairly mild and some of our birds would go down as much as 3 times in a season when we removed the eggs from the first clutch, so what you say doesn't surprise me.
    If you have an opportunity to go to Africa, don't miss it!!!!
    All the best :)

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    1. I would be very interested to hear if climate change is having an impact on other species. I am sure that there must have been a lot of research. Butterflies do seem to be a very good indicator, though, and we have seen the range of several species change over the last few years.
      I certainly want to go back to Africa again one day. I really love the continent.

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  6. I enjoy your passion for butterflies.
    I have barely begun to learn much about them.
    So much to learn.
    Your photos are lovely.

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    1. Thank you Tammie Lee. I think we all have much to learn about butterflies.

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  7. Very interesting, Nick! I would have thought that an extended breeding season would lead to an increase in numbers. It's scary how much the climate change is altering everything around us.

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    1. Hi Sunita,
      Yes, there are so many impacts and knock-on effects of climate change that we probably can't predict. I wonder if our recent cloudy and wet summers are another. The one thing that is heartening is that we appear to have returned to the tempetatures of the late 1700s. It is just the rate of change that is alarming and how far things will change.

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  8. I am not familiar yet with the changes in our butterfly population. However, i think the number of our common leps are also decreasing, but i cannot zero in on climate change much because i don't have data. However, areas i have always been observing them suffer host plants demise because of cultivation. Most specifically the Tigers and Crows always present in a known area are now dwindling.

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    1. Andrea, It is very difficult to know what is going on. In the 1970s there were only 12 species regularly recorded in East Lothian. Today there are 24 species. Many of the once common species are in decline, but some of the species that have recently arrived are doing really well. I guess some species are able to adapt better than others.

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    2. Hi i felt like replying here again after sometime. It is also difficult to know if i am recording all of the species in my area, as you well know i am just a weekend or Sunday morning spotter. Despite that, i have recorde at least 84 species already, which feels plenty. But when you are actually there on the ground, there seems to be very few. I just can compare the difference from my feelings and recall not really on actual data. How i wish i can do also what you are doing.

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    3. Andrea, I think that any records are interesting to keep. I have been looking at the records of the butterflies I saw when I was a countryside ranger in 2001. They confirm my thoughts or perceptions of the number of butterflies we used to get, although they may not be very scientific. I simply record date, location and the number of each species. Even after a couple of years it is interesting to see the differences between years. Since 2001 I have gradually persuaded people to send me their records. There are now about 20 people regularly sending in records and last year we had over 2000 sightings recorded.

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  9. Hi Nick.
    I wasn't aware that the Wall was doing so well in your neck of the woods.
    As you are probably aware I do lots of research on them on my local patch. As far as the 3rd brood possibly damaging them it doesn't seem to here. We had a very strong 3rd brood in 2017 and I am finding large numbers of larva at the moment, even after the big freeze over the past couple of weeks. The last year with a large 3rd brood I also found more larva the following Spring. The larva I am finding at the moment vary from nearly fully grown to just over 1.5cm long.
    I also see more egg laying with the 3rd brood, possibly because they have to get on with it, although the 3rd brood down here often goes on for 5 or more weeks.
    It does seem it has very much become a butterfly found mainly in coastal areas.

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    1. That is interesting to know, Bob. Do you live on the south coast? I wonder if there is a critical length of season. Maybe the Wall can manage a complete third generation where you are, but in other parts of the UK there isn't quite long enough for the caterpillars to develop? It would be really interesting to know. I haven't managed to find any caterpillars yet.

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  10. Yes Nick. Seaford is on the coast between Brighton and Eastbourne. The larva are much more numerous this year. Highest count last weekend was 34. Before this year my highest count was 14 and I thought that was impressive.
    Of course, when numbers are good the predation species also increases in numbers so I can't guarantee good butterfly year for them.

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  11. We are fortunate enough to see a good number of Wall on the Isle of Wight every year.First sighting for me last year was 27April which seems about the usual time here for a first record.Of course the coastal cliffs and chines are the best locations to see this species locally.

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    1. This is interesting Peter. I notice on the distribution maps that they appear to occur around the coast of much of England. I wonder if the frosts are less severe around the coast and the caterpillars can survive the winter. Having worked their way up the coast into East Lothian, they are now starting to spread inland a bit. It will be interesting to see how far inland they are able to survive.

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