After a warm winter  April turned  cold, very wet and dull and everything just about stopped and it was near impossible to walk all month. By May there were already  losses  among our spring species;  down a third in numbers.  June brought Arctic winds, a complete reversal of  the Hot June of 2023 when nine  species reached all time highs here and across the UK.  For the  first two weeks of this June  temperatures  were 8’C cooler than  in 2023 around  a frigid  9’C  with  only 5 good days of sun at the end of the month.  The  first three weeks of July had  the same theme of  cool and damp with 5 warm sunny days at the end. Transect walking for many  was very difficult most of the year.  The  persistence of the cold and damp over such a long period had a devastating effect with numerically two thirds of our butterflies in the critical later stages of their development; mortality was very high. It was  also one of the longest June  ‘Lulls’  lasting from late May to the beginning of July. When the main flight  season did arrive it  was  slow to build up  and there was no usual peak. Better weather in August helped  save the second generation and very unusually numbers actually went up at the start of September.

  Losers

        For many species it was a triple whammy after  the heat and droughts of the previous 2 years and  last July’s poor flight period this year made it a perfect storm. Overall, annual numbers were down 41% against the average and 45% down on last year.  Half our species were down more than 50% and a quarter down more  than 70%. The Lycaenids, Vannesids and the Fritillaries were amongst the worst affected. Many transect walkers did not see  a single Common Blue, Small Copper, Holly Blue, or Brown Argus until late into their 2nd broods..  Four of our long term declining species Common Blue, Small Heath, Small Skipper and Green-veined White  had  their worst year ever recorded. 

The Winners (and less bad losers) 

      Northern Brown Argus  had an exceptional year up near 50%  Other species bucking  the trend were Brimstone and Marbled White. The  damp  loving Ringlet on many limestone/dry sites  were up a half  while on most wet sites they fell by a half.  However if it wasn’t for Ringlet holding up the overall numerical losses, this year would have been significantly worse. It often happens when Meadow Brown has a very poor year, like this one, Ringlet does proportionally better, and vice versa in a warm year. 

It has all happened before… many times.    

It was our worst year since 2016 and nearly as bad as 2009  when numbers  were  down 50%.  2024 comes after a run of 6 relatively good years since 2018  along with  rapidly rising temperatures including 2 of our hottest summers which were followed by two of our best butterfly years in 2019 and 2023. It is  likely 2024 was just a blip 

  When warm summers come in succession  the second year is often exceptional  as it gives a chance for butterfly numbers to really build up e.g. 2018/19, 2013/14 and 1975/76,  the latter being the best butterfly year in living memory.  There is hot and then there is  extremely hot where 2022 and 1976 share many similarities of the  effects of extreme heat and drought that parched whole landscapes. The effect on 1977’s butterflies was catastrophic;  many species  were reduced to such low numbers subsequently they were lost from many  sites  forever. It was  so nearly a  swansong for many rare species but would it repeat in 2023? There were a few reasons to be less pessimistic when the extremely hot/dry summer of 1995 caused a similar  drought, but then 1996 turned out to be an  exceptional year for our butterflies.  Butterflies seem able to tolerate tough conditions up to a point, so  the question was did those eggs desiccate and young larvae perish in last year's extreme heat?    

    Losers:  As we look back, most of us consider 2023 a poor summer with our garden flowers and  buddleia  attracting even fewer visitors  than a poor 2022.  In part this was due to  Peacock and Small Tortoiseshells having a second very poor year. Both these species use nettles in full sun searching out larger clumps with  soft young growth, but, this year’s drought and June heatwave stopped nettle growth,  combined with poor numbers of overwintering adults  led to a second year of steep decline in both species. In contrast in  the cooler uplands  they fared better with Peacock showing signs of recovery benefitting somewhat from the cool wet July.  The Dark-green fritillary was hit particularly  badly,  being lost from new sites it had colonised during its boom years just 2  years ago. Its food plant, Hairy Violet, grows on  calcareous grasslands that suffered the most in last years and this spring’s drought.  In the same boat were many of our scarce species with Northern Brown Argus, Rockrose Brown Argus, Wall and Dingy Skipper all doing badly. Small Heath  had a second consecutive poor year suffering  from drought after booming in the  damp summers of 2020/21.  Moisture sensitive species like  Green-veined Whites  fell to a 15 year low and Ringlet, our second most numerous species, which favours damp areas, had a poor year everywhere.  Half our species were down against their 5 year averages. 

    Winners: The July rains made for perfect conditions for large numbers of  Red Admirals arriving  from Europe booming  on the soft young nettle regrowth caused by the July rains;  It was their best year ever.  It was easy to count dozens of 'clipped' nettle heads on a countryside walk where developing Red Admiral caterpillars bite part way through the nettle stem causing the head to fall over on itself allowing the larva to make a larger safe nest.  Comma  boomed for a second year to its  best year ever,  because it choses nettles in part shade that suffered much less in the June heat and was also likely  helped by less parasitization due to decline in other Vanessid species.  It produced a bumper  ‘hutchinsonii’ summer  generation.  Out in the countryside, particularly woodland and hedgerows it was a really  super year for many of our Brown species particularly in the vale of York and river valleys; the only exceptions being  sandy sites. Gatekeeper, Meadow Brown, Marbled White, Brimstone, Cranesbill Brown Argus, Holly Blue and Speckled Wood enjoyed a second very good year; and all had their best year ever on our monitored sites.  All these species also happen to be winners of climate change . Small Skipper with Small Copper also saw a significant increase after a run of poor years and both always seem to respond after hot dry summers. 

        As it turned out 2023 had an old fashioned cool spring followed by an old fashioned wet summer pierced by the  hottest June ever.  June is very important as the ‘formative’ month of  summer when so many of our summer species are in their final larval or pupal stage when both growth and mortality from  predation are highest so the quicker/warmer it is, the faster they get through it, and thus more survive to adults.  When only a few percent ever survive to adulthood  a change of just 1-2% more surviving  can create big  booms. To an extent this is what happened to species not affected by drought/ thin soils. The largest contributor to overall butterfly numbers is always  Meadow Brown which was up 40% and  would have created a record butterfly year on their own except  the second most common butterfly Ringlet, being drought sensitive, was  down 20%,  so overall numbers of butterflies for the season were  up 9% on the 5 year average  but still  so close to the all time high in 2014.  2023 could so easily have been that  exceptional Butterfly Year had the weather been a tad better in spring and especially July and August…Oh so nearly.. but it could have gone either way!

2022 Weather  

Autumn 2021   was very sunny, warm and  great for our hibernating adults to build their fat reserves and survival rates were high.  November when many species caterpillars enter hibernation was dry and early December cold which generally helps survival  from  fungal disease.  Winter was very mild with January sunny  and  February  warm and wet. Spring was warm 1.3'C up on the average , sunny  (50% up in March ) and very dry particularly East Yorkshire,  Summer was very hot up 1.7'C with a heatwave in mid July peaking at 40'C in the south of the county. Summer rainfall was less than half average and with the dry spring it seriously limited plant growth and nectar supply.  Crucially most of us had a short rainy spell in July that  partly revived grasslands but the burning sunshine was relentless in South Yorkshire.  The heatwave  returned in August and  the season ended abruptly with lack of nectar shortening  lifespans and driving hibernators to aestivate early and not reappear. 

The chart below shows highlighted in green the two highest count  sites for each species from the  last 5 years . As with previous years the Forest of Flowers scores are highest  and has the highest for 5 species.  Almost every site has the highest score for something which is reassuring we have a good spread of habitats to represent what is happening in Yorkshire.  The site with the largest number of top scoring species and  possibly the most species rich in Yorkshire remains Fordon Chalk Banks and close second is the Forest of Flowers , Malham Tarn , Bastow woods and Bishop Wood with Kiplingcotes , Brockadale and Whitcliffe Scar not far behind.  NB some of our rarer species are not included due low numbers of sites

Speckled Wood  has the longest flight periods  of any of our species and can be seen anytime between February through to November.  These days  it occurs in great range of grassy habitats providing there is a bit of shade which is its main requirement.  It was very different just 15 years ago when it was  much more constrained to deeper shade of  woodland . Since the two very wet summers of 2007-8 Speckled Wood has really spread at the local level and has become almost a garden insect replacing Wall which virtually disappeared in those two wet summers.  Climate change particularly recent warm wet summers is producing lusher grass growth aided by nitrogen disposition and these are now key drivers in the long term trends.  Speckled Wood produces 3 generations on the lowland and 2 in upland areas. 

The Wall remarkably occurs on 15 of the 45 monitored sites, up 2 on last year, but this is now a rather rare butterfly and south of us into Nottinghamshire it is extinct and is just hanging on in the White Peak and Lincolnshire coast. It is rarely seen in the Vale of York particularly south of the Ouse  Before 2007 Wall was almost a garden butterfly that most of us took for granted illustrating how quickly things can change. It moved from near threatened to endangered on the new Red list this year.  As its name suggests it has a strong preference for warm bare ground where it selects sparce vegatation with a dry warm microclimate to lay its eggs. This is in strong contrast to its close relative the Speckled Wood which is enjoying the warm wet summers and abundance of lush grass while Wall fortunes have plummeted and is only found in  numbers in a few distinct colonies on the coastal strip and uplands. These areas are cooler which seems a paradox for a heat lover but popular reasoning for its demise is  because the caterpillar has to reach the fourth instar to successfully hibernate. Climate change now allows  for a third brood of adults  but this is too late in the year for the caterpillar to reach the fourth Instar and it turns into a suicide generation. Other disagree and believe it is much more to do with nitrogen disposition increasing grass growth cooling and humidifying the microclimate greatly increasing  larva mortality rates till it dies out ; which indeed it  did in the cool wet summers of 2007-8. It  seems  it can still prosper where nitrogen disposition is low such as our uplands and coast where it can also have a third generation as  it did more strongly this year.   Whichever view is correct this species still makes sporadic appearances on quite a few of our lowland sites. 

Long term after a big drop in 1996 folowed by a short recovery 2004 was the last year Wall was a 'common' butterfly. The following  wet summers seemed to  be its death nell with a few brief reappearances there was nothing  much till  2016 and with the aid of a run of warmer summers and dry springs we seemed to see a resurgence till now 40% of our sites this year have seen it reappear in moderate numbers. This now includes the north end of the Vale of York.  South of  York so far there is only  a hint  but we might stil be at the beginning.  This is a 600%  increase in abundance since 2015. 

2021 Weather Highlights

2020 finished  mild dry November  but then a cold wet winter. A very short ‘heat wave’ at the end of March was followed by a very cold sunny April and cold  verywet May. Summer was warmer than average but often cloudy. September onwards has been very mild while November was dryish.

Prospects for 2022

• Lower numbers of hibernators but survival should be good after the Indian summer.  

• Another ‘dryish’ November should help survival of  the Browns and other species

• Holy Blue may well have reached it low point and first signs of improvement

• Whites did stage a slight recovery in the Indian summer. 

• We badly need a sunny summer to help the Lycaenids recover.

• What will be the next invading species? Purple Emperor?

Overview

The season was rather dominated by the pandemic and we were unable to record for the first 6 weeks of the 26 week recording season but a majority of recorders  managed to restart in May or June and then put in their normal number of walks.  We appreciate the charities suffered and staff were furloughed and unable to undertake their duties and some of us were shielding. We hope they will be back in 2021 as the last lockdown comes to an end  but preparations are behind and may make it difficult to repair some of the losses in 2021 .

The Weather

 After a very wet and warm autumn in 2019 with floods which returned in late  February to be promptly followed by lockdown 3rd week of March! At which point the sky cleared to weeks of glorious sunshine and record breaking temperatures and more importantly a very dry spell which is becoming a feature of recent spring weather. Few can remember such an early and protracted spell of fine weather through April and then into a heat wave in May.   As a consequence  many species emerged very early and we were not there to see them. Some were already in decline or had finished before our first recording day in mid May as the lockdown rules were eased and transect walking was allowed once again.  By this time the heatwave had really set in, the ground dried and cracked and dryer grasslands suffered badly with plants stunted and withering lower leaves. Some plants were only half their normal height and size. The spring  and early summer species were emerging nearly 10-14 day early with 23 species in the UK recording their earliest ever emergence: an exceptional year. Hopes were high that unlike 1976 the heat waves of 2019 would not be followed by a disastrous decrease in numbers of 1977. It has not repeated; and most species came through although there were more losses than gains.  The weather broke in the first days of June and went in reverse with a cool June and a conveyor belt of Atlantic storms which pock-marked the rest of summer particularly a stripe across the midlands into Yorkshire. The summer in many ways was a disappointment after 2018 and 2019 but there were good spells between the storms.  Finding good days with sun and temperature were often hard even in high summer. The  end  of the season was average

The Results

A summary of all sites was prepared in spreadsheet form below.   For each site the percentage change from the 5 year average is shown for each species.  The  number of negatives and positives are then totalled  and the the first conclusion was many more species were negative (14 ) that positive (9) with 3 uncertain.  Included is also the national trends of 2020 compared 2019 and compared to a much longer 10 year average.  2020 follows on as a good year with a pattern now of three good years although 2020 is somewhat down on 2019 

As ever there is a good deal of variation you might expect for a biological organism  but still we can draw a few trends and use them when interpreting each transect later. 

The golden skippers were both down a lot which could be weather related as they prefer longer grasses which had their growth stunted in spring 2020 particularly on dryer  limestone sites  of the tabular hills like Pexton Bank . In contrast after the winter  flooding on some sites in winter you can pick out  some increases on wet sites. 

Large and Small Whites were up a little maybe with the good spring and a second generation but  there was considerable variation between sites. In contrast  more moisture loving  Green-veined White was somewhat down particularly on the dryer limestone sites.  Due to the necessity to estimate during  lockdown 1 we cannot be certain about Orange tip or Green Hairstreaks.  

 Small Copper shows no pattern and  although strong differences as does Brown Argus  and Common Blue a slight decrease but with a  good deal of variation.  Holy Blue is a little uncertain due to the small sample size.

The Vanessids were interesting with the migrant Painted Lady nearly absent and Red Admiral well down along with Comma. Peacock also showed a slight decrease but the highlight of the year was all sites had many more Small Tortoiseshells  which had a  boom year on many sites. This was particularly pronounced in the north of England

Dark Green Fritillary had a good year while Silver-washed on one of its main sites Bishop Wood was average, but sample size makes thes conclusions uncertain 

Possibility for the same reasons the drought probably played a part in the  Skippers and Green-veined White being down Speckled Wood suffered bad losses in 13 out 17 sites and Wall Brown suffered equally badly

The Browns in general were a  mixed bag with  the damp grassland loving species not fairing so well with Ringlet down in 11 of 18 sites and Gatekeeper down in 6 out of 8. 

In contrast Meadow Brown emerged well with increases in 11 out of 18  while the fine grass loving Small Heath had a very good year only down on the thin limestone soil at Hawnby.  This could be they finished their development earlier than the later species and were therefore less effected by drought

National Comparison

When compared to the national picture there is quite good agreement with this analysis of selection of Yorkshire UKBMS transects below . Both  Large and Small skippers being down and Dingy up  while  Small and Large White were also up . 

It is tricky with the spring flying species as we have so few accurate numbers for Orange Tip or Green Hairstreak however there is a close match with the increase in Brimstone numbers. Common Blue was down as was Red Admiral and Painted Lady teh later by 99% which matches the rest of The UK . There is very good agreement that Small Tortoiseshell seeing a 130% increase.  In yorkshire the  Peacock were down while nationally they were up. Comma was down in Yorkshire as well as  nationally.  Dark Green Fritillary we are in agreement  with national and they had a good year.  We agree that both Gatekeeper and  Ringlet were down nationally and in yorkshire but in Yorkshire Meadow Brown  and Small Heath was up .

 June:  in the final days of May when the  ghastly spring  finally gave way to sunshine and warmth.   This was promptly followed  by the traditional June lull that has proven to be exceptionally deep and long  because  of the cold wet spring causing species to emerge two weeks late in many cases despite June being largely sunny , dry and warm .  The disastrously low butterfly counts  of May  have continued till the third week of June when our summer species began to really take off, but, much slower to build than normal.July: Despite being one of the 5 warmest July's on record with the mid-month heatwave  peaking  near 30'C it was also wet.  Rain was very local with some parts suffering flash floods, mighty thunderstorms and huge hailstones,  others nothing . Global weather continues to be driven  by  weak and undulating  Jetstream bringing heatwaves and floods in equal measure. 

August: As the end of  the season  approaches,  a question I've been asked is "Did we have a summer?"   Its easy to forget  the July heatwave and while in Europe it continued well into August with some of the highest temperatures ever experienced, and devastating wildfires,  our heatwave broke up in late July  to  a procession of  rainy days and sunny intervals.  August had average temperatures but has been, in large part, cloudy with mists and drizzle and any sun quickly extinguished with convective cloud bubbling up in minutes.  Good sunny spells have been days apart and opportunities have been scarce to get out and explore and  our transect walkers have struggled to find a suitable 'slot' to walk in, although the north of the county it has been significantly sunnier  A blocking high pressure just west of Scotland established in the last 2 weeks drawing down cool  NW winds from Scandinavia and  the forecast  into September is  to remain dry but murky. 

September: The season has ended suddenly with numbers tumbling on our transect walks in the last week of the month,  despite the good weather. . September temperatures have been well  over average by near 3'C after the mid month mini heatwave  hitting 27'C and more September records being broken!  It has been quite sunny as well as dry but counts on our transects have often been single figures from mid month and rather a disappointing month.