April 2023 The season has a slow start but some species are doing quite well despite last year's extreme heat like the Orange Tip : we take a detailed look at its status and how it is changing over the years
One of the most uplifting sights of spring is the rich orange of the male Orange Tip. It is beautifully complemented by the green 'parsley' of its underside that works as a brilliant camoflage when roosting on the flower heads of Cow Parsley and with the orange tucked away beneath it becomes near invisible. The closer you get the more beautiful and intricate patterns become... Can you see the bright yellow eye liner? The green colouration is actually made up of a variable dusting of black scales mixed with yellow scales along with white and is not green at all.
Yorkshire has always been near the northern limit for this species which declined to a low point by 1940 when it was largely confined to South Yorkshire and a few sheltered woods and valleys elsewhere. As global warming accelerated especially during the warm spells of 1975-76 and 1983-84 rapid expansion occured which continues to this day (10% in the last 20 years see graph below). Over the same 80 years the Orange Tip has largely lost its prefered foodplant: Cuckoo flower or Cardamine pratensis from which the butterfly gets the second part of its latin name. This plant was once common on damp meadows but is now a threatened species in parts of Europe. Agricultural intensification has caused the loss of 98% of our traditional meadows and along with drainage and laterly nitrogen pollution cause stronger growing sedges and grasses to outcompete and stifle Cuckoo flower. Nitrogen is one of the gravest threats to many of our butterfly species. Over the last 40 years Orange Tip has succesfully switched more and more to Garlic Mustard as its foodplant which has thrived in the recent run warmer wet springs and prefers a rich soil helping the butterfly population boom near fourfold in the last 20 years (See graph) This boom is mirrored through Europe with the switch to Garlic Mustard . Eggs are laid on Honesty, Dames Violet and Hedge Mustard but larvae do not often survive. 2019 was the last boom year and this next week will see the peak of its flight period ..Could 2023 beat it??
2022 A 'Hummer' of a Summer: A year of extreme heat, migrants, drought, parasites, booms and busts.
Summer 2022 will be memorable not only for the intense heat but also for the many migrant Humming-bird Hawk moths which graced our gardens sometimes more than one at a time... an exceptional year for many moths and butterflies.
Highlights of our Yorkshire species were Holy Blue who after a population low in 2021, due to the cyclic peak in its parasite, bounced back, with a 20 fold increase in the spring generation. Comma had a exceptional summer generation doubling in numbers after 2 years of decline. Gatekeeper had another good summer as did the other Browns and Speckled Wood boomed in late summer. In contrast Small Tortoiseshell after two years of boom went bust and took Peacock with it to a new worrying low. The reason seems to be not only a boom in the parasitic Tachinid fly Sturmia bella, but the poor nettle quality plus the heat drove hibernators to aestivate very quickly and not produce another generation.
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.
30 years of Weather : A long term review of it effects on our butterflies
The chart below attempts to link overall butterfly abundance (by adding together the index of each species) and average summer weather factors (for June/July/August) including average daily maximum temperature, sunshine hours and rainfall. Each factor is scaled so the data graphs overlap to help illustrate any inter-relationships. Both mean max daily temperatures, sunshine hours and rainfall closely follow abundance although of course with rainfall it is in reverse i,e, low rainfall linked to high abundance ie sunny ! Teh abundance index is the average of the totals of all species on each of our monitored sites.
It clearly shows the good and bad years although different species on occasion reacted differently. Of course there are othre factors and in the last decade the abundance peak is often lagging a year behind the weather peaks. The variation in overal labundance is quite remarkable with a low of 260 in 2009 to highs of 1100 in 2014 and 2018 , It shows the doldrum years of 1997-2000 then the bad summers of 2007-2012 with 2009 being the worse in modern times. this was the followed by the best two summers in this 30 year series 2013/14 which just tops the previous 1995/6 peak, Following a short dip till 2017 there has been a prolonged period off higher abundance with warm, sometimes wet summers and a pattern of dry sunny springs. alos on the chart you can see the trend lines for temperature in orange and abundance in purple and the slope is remarkably similar is likely not a coincidence.
Abundance has risen 18% over the 30 years but there are now signs that this is accelerating while average max summer temperatures have risen 0.9'C ( mean 0.7'C) and spring temperatures a similar 0.7'C and again both shows signs of accelerating. Summer rainfall has risen 27% but the number of rainy days by only 7% meaning rain is very much more intense as sunshine hours have risen as well by 2%.
This review is based on 50 sites with historical data sufficient to allow trending of results. Our monitored sites cover a wide variety of habitats from the wettest bogs to the driest quarries, flood plains to limestone pavements, from calcareous grassalnds to country lanes, ancient woodlands to city centre greenspaces even around a beaver lodge. However the list also contains some of our best butterfly reserves which are carefully mainatined and you might think this over represents our scarcer species. See chart of totals from all monitored sites:
The chart above is likely very different from your sightings in your garden or the agricultual fields and hedgelines beyond. Everyone will have a different opinion of which was our most common species this year but of course it depends where you look. Our gardens are not typical and as they often have abundant nectar can concentrate some species much like our sites on nature reserve might have large numbers of a scarce species. The official assesement of the 'relative' abundance of our species is achieved by the wider coutryside scheme but we have too few in Yorkshire to interpret. However from our weekly UKBMS we can calculate trends but we are ONLY looking at changes in abundance and not absolute numbers. This allows us to be pretty sure about overall changes going on throughout Yorkshire including many species that do not occur in the wider countryside. Butterflies like all natural organism communities have ups and down or we would drown in them. Butterflies can complete their whole lives in a matter of a few weeks and can multiply at astonishing rates but are highly dependant on weather as well as being in a fine balance with their predators, like birds, or parasites and disease. Changes can be 10 fold or more annually, up or down, and this wil be different between locations, habitats and species. So as well as measuring average change across sites we also look at the consistancy between sites by the number sites that have increases or decreases. Generally this follows the trend but you can be much more confident if it happens on the majority of sites. Sometimes it leads us to realise that different habitat or different parts of Yorkshire are responding differently or indeed the management on a particular site has caused a change. Since this is something our site managers really wish to know it is only by our careful analysis of other factors can we attribute a change to the site rather than external. This makes our transect data way more valuable a tool for conservation of our species because, as you will see, it leads us to understand what is going on and the drivers in a fast changing natural world. It is incredible to look back 40 years and realise we have seen more than 10 species recolonise or spread very quickly through the county since the first in a series of warm spells that continue apace. Abundance changes quite a long time before distribution changes as a result, so, our work is very much an early warning. Distribution maps only show occurance and dont show decline until your close to extinction.
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
The table attempts to illustrate the trends in recent years and compare to the rolling 5 year average and compare this with the long term national trends. It shows for each of our common species the change compared to last year, the number of sites up or down against the 5 year average and this same measure in each of previous years. Lastly it shows the long term trend nationally since 1990. With many more sites this year we have also looked at the effects of altitude and landscape on abundance and looked at Yorkshire trends over the longer term (10-15years) where our systematic data allows.
The Hesperiids (The Skippers)
Both Small and Large Skipper improved on 2021 particularly Large Skipper to near the 5 year average,
However there is a consistent long term decline of Small Skipper which continues apace having lost more than 50% in abundance since 2002 (12% in last decade) which is worrying for what used to be one of our most common butterflies. Year to year it shows a great variation in abundance by a factor of 5+ but generaly follows the weather patterns booming in 2006 then again in 2014, both good summers but this was not repeated in 2018-19. There are signs the trend is stablising at a lower level but there has been no repeat of the booms in the present run of good summers.
There may well be a combination of factors of not only higher temperatures but also nitrogen deposition altering habitat and suitability of grassland, We are already beginning to loose this species from some of our managed sites
Large skipper is showing signs of recovery with a steady increase of 50% in the last 20 years (20% in the last decade). It enjoys damper as well as warmer summers as do most of the skipper family who are steadily moving north right across europe from their southern homes.
Dingy Skipper was down on its major Wolds sites but up elsewhere and was seen on more sites this year indicating dispersal. Long term abundance change has been pretty flat down 6% in the last 10 years. It was held back in 2022 by drought on the dry limestone sites where brid's foot trefoil suffered badly. The last boom period was 2013-14 as for many of our species
This mobile opportunist seems perfectly able to find and colonise new sites particularly brownfields favouring those with a good deal of bare ground as well as an abundance of bird's foot trefoil. It has recently been removed from the red list as no longer 'vunerable ' to 'Of least concern',
The Pierids ( The Whites)
Brimstone Its Buckthorn foodplant is relatively rare but the recent trend in planting this species as part of farm stewardship and butterfly city projects along with climate change is pushing its range northwards. This highly mobile hibernator overwinters in woodland and showed well this spring, up 30%, This species sufferes greatly from predation from birds particularly the tit family taking large numbers of eggs , larvae and the pupa. The pupa has a uncanny resemblance to a blue tit complete with beak and eyes and characteristic bird shape. To counter birds the Brimstone female tends to select small plants standing on their own away from larger bushes which might attract searching bird looking for easy food. Birds had a much better spring this year than cold 2021 which might have led to heavier loses. Certainly most of the eggs laid in March and April and well into May were predated. Indeed numbers were a bit down in this summer's generation which only flew for a very short time before quickly hibernated in the heat and very few were seen later which is slightly worrying. Generally brimstone will re-awake to feed up on late flowers before finally hibernating for winter, Maybe it was just too big a gamble if they entered hibernation low on reserves.
Continues to show a fast increase in abundance by an incredable factor of 3-5 fold in the last 20 years (130% in the last decade) and +18% in 2022. One of the real winners with climate change and yorkshire remains the northern edge having not yet reached Scotland. It first appeared on our monitored sites down in the south in 1984 just as many other species did at that time but only reaching the Tees in recent times
Large White was somewhat down and its abundance has fallen 25% since 1995 and -10% in the last decade but does show enormous variations year to year. Up to 2012 the downward trend was much steeper at over 50% loss but 2012 was one of the worse summers for 40 years for almost all butterflies plus the very poor 2007-8 wet summers. Since then it has rallied a good deal with the recent run of warm and sometimes wet summers. However overall it is a climate change loser. It is interesting to note it is very responsive to a good summers like 1995, 2013 and, 2018 but good years were always followed by a fall possibly from the longer term effects of drought after the previous hot dry summer prefering damp as well as heat like 2020. The peaks are likely to be much influenced by migrations from the continent in addition. Decline may also be influenced by agricultural intensification and the use of neonicotinoids on rape applied widely from 2002-2013 but then banned on most cropswe might still be seeing a slower recovery from its long lasting residues.
Small White rose slightly this year. Since 1995 there has been a small decrease of 4% . Since 2003 there has been a very significant dip till the good summer of 2013 and fall back as with Large White and a run of poorer summers and then again in 2018 a spike just like Large white and they do mirror each other. However it is interesting to note that neonicotinoids were first used widescale in 2003 before their complete ban in the EU in 2013. Small White populations are now very significantly higher by a factor of 3. The peaks are likely large migrations from the continent coinciding with two good summers of 2013 and 2018. There are very positive signs that since 2015 there has been a strong increase but will it last? Also on the positive side the trend to sow late summer cover crops of mustard and radish to conserve expensive nitrogen and stop pollution of drinking water may well help both these species in the longer term.
Green-viened White numbers held up well even with the drought. This year was typical with the second generation twice the size of the first with highest numbers in our wet woodland sites of the vale of York. Although recentlly the annual counts have been remarkably similar looking back over the last 30 years there has been a good deal of short term variations. Since 2003 there has been about 50% reduction with about 35% fall in the last 10 years, However after the big rise in 2003/4 there are signs this has slowed and gone negative since 2005. The peaks seem to correspond with good summers noteably 2003 then 2013/14 and 2018/19. This species prefers damp sometimes shady places to breed.
Orange Tip has nearly doubled since 1995 and has risen 20% in the last 10 years and was consistantly up again this year and the short term rate of rise is currently very fast. It continues to increase its range being seen in higher altitudes this year and is a beneficiary of climate change and warm wet springs in particular which delivered the big peak in 2019 after another warm spring previously in 2018.
The upland sites peak two weeks later than lowland ones.
The Riodinids ( The Metalmarks )
Duke of Burgundy had a better year on its key managed site comparable to the recent high in 2019 which is encouraging. Although down 11% against the 5 year average it was a healthy 15% up on last year. Longer term abundance on this site is declining, but slowly at about 17% in the last 10 years which might be caused by bracken encroachment in open areas although regular management takes place for scrub ingress along its western boundary. On other sites it still shows recovery and extensive conservation work continues and it has reappeared at Pexton Bank showing the gathering strength of the Pickering metapopulation. UK wide its recent improvements has moved this species from endangered back to vunerable on this year's revised red list
Lycaenids ( The Blue Family)
Small Copper's long term decline continues. 35% since 2005 and -20% over the last 10 years. This year down -18% against the 5 year average after a series of poor years there seems little connection to seasonal weather. This species is known to be sensitive to nitrogen disposition much like Small Skipper. Its last good years were in 2018-19 and previously 2010-11.
Small Copper generally has 3 generations annually with numbers building up with each succesive generation and the third (September) generation tends to be strongest and this year was 5 times that of the first.
It suffers very badly with a Braconid wasp Cotesia cupreus. The wasp larvae overwinter inside the caterpiller but emerge just before its host is due to pupate in spring. This parasitoid is a specialist in just the copper species and may account for the wide extremes of nearly an order of magnitude in population as seen in the graph but there are likely many other factors. The parasite appears to take a very high proportion of the overwintering generation.
Northern Brown Argus
Northern Brown Argus was quite a bit down -35% against the 5 year average with a similar decline to regular rockrose Brown Argus This is very likely due to the very dry conditions on calcareous soils.
Since intensive monitoring started in 2013 there are have been two peak years 2014 good summer along with 2016. 2018-19 hot summers were also good. Prior to that 2010 and 2006 were good years with extrememly low numbers in 2009 and the wet cool summer of 2012 the worst in many people's memory
Abundance longer term is going up quite rapidly at 90% and 43% in the last decade it seems to have manged to shake of the crashes in 2007-9 and the worst summer in living memory in 2012.
Brown Argus until the millennium was limited to calcareous grasslands but is now seen on a wide variety of sites with the very rapid spread of the migratory cranesbill feeding form, particularly farm stewardship belts where its favourite host Doves foot cranesbill thrivesas a pioneer plant in tracter wheelings. The second generation is generally twice the size of the first but not this year where it was down about a fifth with a poor showing in August with obvious signs of stress on the rockrose from drought (see graph). In stark contrast sites with the cranesbill form boomed on more mineral soils of lowland sites. It seems a paradox that none were seen till August suggesting what we see have come from somewhere else, possibly neighbouring farmland where dove's-foot cranesbill is a common agricultural weed. The migratory form also exists at much lower populations and are highly mobile but in hot years can really get going with even a third generation being seen. This local movement was seen in our data with the number of sites increasing from 2 to 9 and abundance tripling at the same time and the best year so far. There has been a increase in abundance of 65% since 2010 and 40 % in teh last 10 years. This year they were likely attracted to nectar on our managed sites as it was often seen nectaring alongside Common Blue. It is likely to disappear from these sites next year, as is it's habit.
Abundance has risen 65% since 2010 40% in the last 10 years
Common Blue An increasing number of sites with a partial or complete second brood as a result of warming climate. The switchover to 2 broods from one is currently happening at about 150m altitude ( ie approx 1.5'C warmer) and the graph shows the comparison with sites above or below 200m(Upland). Above 150m or in warmer years the July gap begins to fill in with single brooded and three peaks appear.
The trend this year is down a bit on last year by -18%. Drought has certainly almost killed Birds foot Trefoil on chalk sites where there was certainly decreases in numbers but lowland sites tended to see small increases suggesting better breeding conditions were offset by drought.
Long term has seen a decrease which since 2007 is about 7% and barely changed in the last 10 years . Good years include 2010 , 2014 and 2018. The pattern is similar to the other blue species responding positively to warm summers and strongly negative to poor. Bad years are 2009, 12 and 16. The difference between peaks and trough are about a factor of 3 and sometimes greater on individual sites.
Holy Blue is the spectacular winner of 2022 and is following the boom part of a boom/bust cyle with its host specific parasitoid Ichneumon fly Listrodromus nycthemerus. In a bad year, like last year, it can parasitise more than 99% of larvae causing the complete collapse in our garden populations like we saw in spring 2021. The bounce back this spring is equally fast, up over 20 times compared to spring 21 and a new cycle begins and repeats every 4-5 years with the last peak in 2018 and before that in 2014, then 2011 and so on. Although up by a factor of 5 on last year which was close to the bottom of the cycle and a 8 to 10 fold difference between the peaks and the troughs which you can see in the graphic is teh most pronounced and reguler of all our species.
You have to consider if it is warmer springs are making the parasite less in sync with its host rather than the butterfly benefitting directly and there is evidence to suggest this. This years second generation the parasite was already coming back and the increase over the whole year dropped back to just 5 times last year and double the 5 year average, so, we may have already peaked. There was also a small 3rd brood this year. It loves graveyards being one of the most common butterflies at York Cemetary outnumbering even Meadow Browns this year.
Listrodromus nycthemerus searching for Holy Blue Eggs
The long term trend is 120% up since 2003 and 32% up in the last ten years. Holy Blue is a real winner with climate warming increasing its range in addition and moving upwards in altitude beginning to colonise upland over 200m.
Red Admiral had a much better year after two consequentive poor ones. There were emergences from hibernation but they were greatly outnumbered by early migrants and the whole year was punctuated with waves of migrants. There was a 9 fold increase this Spring compared to 2021 and a 40% increase over the whole year and 26% up on the 5 year average, This species has not suffered unlike the Small Tortoiseshell and Peacock bust . Like Comma, larvae are solitary throughout their lives making them somewhat less susceptible to Tachinid flies that have boomed on gregarious caterpillars this year.
Longer term abundance is rising again quite fast at 125% since 2003 and 33% in the last 10 years. This follows a fall until 2010 especially the a succession of cool wet summers of 2007-9. The big peak year was 2017 and to a lesser extent 2019.
Painted Lady , This migrant was up a tad this year compared with last, but well below the last boom year of 2019. Small waves of migrants arrived regularly along with Red Admirals and Humming-bird Hawks.
Before 2019 the previous big wave of migration was back in 1996.
Other significant 'Lady' years include 2000, 2003, 2006 and 2009
Since 1990 there has been an increase of about 25% in abundance.
Small Tortoiseshell has boomed in Yorkshire these last two years finally crashed to 40% of last year but this hides the fact that there was a particularly poor summer generation and no third generation. Caterpillars I raised from our local nettles hatched only Sturmia bella which has become the dominant parasite of this species with its lifecycle closely aligned. The parasite lays tiny hard eggs in large numbers around larval webs which the caterpillars eat whole. Some of our sites have seen zero adults since mid June seemingly the whole second generation was lost simply because they hibernated rather than reproduce or were lost to Sturmia. Nettle quality is very imprortant and after 2 years of good lush nettles in warm wet summers aided the boom in numbers. If the first generation feeds on poor quality nettles then the adult is way more likely to hibernate rather than take the risk of laying eggs on poor nettles and fails to mature sexually and hibernates. Some sites in the north of the county were much less affected however. In southern UK, 2021 was a very poor year for Tortoiseshells while in Yorkshire it boomed suggesting this might be Sturmia parasite moving north. Sturmia originates from southern Europe but has moved north responding to warming. It arrived in southern england in 1998 and spread rapidly reaching Yorkshire about 4 years later. Since its arrival Small Tortoiseshell has suffered some serious periods of decline nearly disappearing in some counties but it has proven impossible to blame this all on Sturmia although it has certainly been a strong influence.
No 2nd generation occured in August!
Long term this species is slightly down 12% since 1993 and 4% in the last 10 years. It has seen considerable variation which has become greater since the arrival of the Sturmia parasite around 2002 varying by a factor of 10 to nearly 20 fold between seasons. This is most certainly only partially down to parasites and the graph illustrates a very strong link with peaks in good summers like 1996, 2003, 2013/14 2019/21 and troughs very much with cool summers. The period 2005-2012 is the reason that the trend over the last thirty years is slightly down . Recent warm wet summers do seem to be suiting this species and the 2019 boom has been a long one lasting to 2021 when despite really good overwintering conditions after a very good autumn resulted in excellant numbers then this summer's heat, drought, poor nettles and Sturmia ment no second generation. This species is adapted to dealing with these conditions and if nettle quality is poor they do not sexually mature at pupation and go direct into hibernation on emergence as adults. This is being seen more in the south of the country and could account for a much more significant downturn there.
Sturmia bella adult has the typical white head and grey striped body of a Tachinid fly species. Parasitised host pupa contain 1 or 2 fly maggots which brake out and descend by absailing down protein threads. On descent they pupate immediatly.
It can infect most Vanessid species but is only really deadly to Tortoiseshell and Peacock. It can infect Speckled Wood and the overwintering host is unknown but if it turns out to be Speckled Wood then it might explain why Sturmia seems worse in woodlands which are normally the strongholds of species like Peacock.
Peacock overwintered well and emerged in good numbers. The summer generation is generally large and 4 times the spring abundance but this year it was barely half and disappeared very quickly within a week and almost none have been seen since as shown in teh phenogram.
It seems this species faced the same problem as Small Tortoiseshell and its prospects in 2023 could be dire. Another paradox is on the south coast this species produced a significant second generation for the first time! 2nd generations are now becoming normal in Northern Europe
Longer term this species follows the general trend of Small Tortoiseshel and many others with peaks in the good summer years namely 2003, 2006, 2013-14 , 2019 Abundance has risen just a tiny amount of 3% in 20 years but the peaks and troughs are very much more pronounced. The variation is also great being about a factor of 8-10. It also suffers to a lesser extent with Sturmia and in the same way as Small Tortoiseshell the 'ups and downs' are now considerably higher than prior to Sturmia
Comma really is a paradox this year booming while Peacock and Tortoiseshell crashed. Overwintering numbers were good but the summer generation was 6 times higher than last year and over the whole year abundance doubled and was also up a quarter on the 5 year average after two poor years. In addition the increase was consistent across sites. Comma lays eggs singly on nettles in the shade with females being very fussy to find lush growing plants while the other vanessids lay in full sun This could have saved it from the poor quality nettles. You can also ask did the collapse of Tortoiseshell this year and their boom the last two years when Comma numbers were rather low indicate interaction with another unknown parasite species?
Longer term the abundance of Comma follows good summers with peaks in 2006, 2010, 2018/19 and has increased 20% over the last 20 years and 6% in the decade and we are currently at a all time high.
Small Pearl-bordered Fritillary
Small Pearl-bordered Fritillary had a good year on the North york Moors with a 20% increase against average and double last year however we still wait for a full set of Dales results.
Its long term fortunes have been rather mixed partly due to the very small sample of sites monitored which is averaging about 6 equally split between the North York Moors and the Dales national park. In general we are seeing a decline of very approximately -40% in the last 20 years but more importantly an improvement since 2008 by about 30%. 2017 was a universal poor year across Dales and Moors sites. Since then there has been an improvement in every year after this apart from 2021. The two key Dales sites show opposite trends in recent years with Scar Close increasing dramatically while Swarth Moor has not recovered to its previous levels which might indicate habitat change.
Dark-green Fritillary had a poorer year, down about a third on the average, after two good years. This species is a big winner with climate change this powerful mobile butterfly is continuing to spread into new limestone areas. On lowland sites it peaked in mid June while upland sites not till nearly a month later. Its spread up the limestone ridge seems strong with many stable colonies around the Aire, Wharfe and Nidd gorge . It is utilising Hairy Violet most commonly which is restricting it to just Fordon Bank on the north most corner of the Wolds. It also uses Dog Violet in calcareous woodland situations. Strangely this species has moved from least concern to near threatened due to loss of sites in Scotland due to agricultural improvement and increased sheep density.
Long term this species sees a 26% increase since 2008 and 13% in the last 10 years
A fast powerful insect with a wing shape like the Monarch was thought to be a rather sedentary but this views seems incorrect. No other species, unlike the many that have returned to Yorkshire in recent years, has had such a rapid spread and explosive increase in abundance since its arrival back in 2017-18. It reached almost all corners of Yorkshire with a boom in numbers at key sites in 2019.
2022 sees another boom with it reappearing in many locations it had not been seen since 2019. Most of our sites saw a strong increase and there has been a good deal of dispersal. However at its heartland in Bishop Wood, Selby there was a significant decline simply because of the huge amount of forestry thinning and ride widening during winter 2021. This accounts in the dip in the curve However this work will ultimately be very much in this species favour, but the heavy machinery does take its toll on its breeding areas short term. You can now expect to see this species wherever there is suitable lowland woodland in Yorkshire. Its current trend in abundance is 140% since 2018
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.
At the start of the season there are secondary peaks in the flight curve due to how this species overwinters which can be as a pupa or a third stage larvae which can in addition come from either slow 2nd or quick 3rd generation larvae of the previous year as development times vary considerably between individuals. In addition the proportion of larval and pupal hibernation can be very variable with location and season and between 10-50% split in favour of larvae. The earliest emergences are pupa hatching but numbers are often low and then a second peak in May from those that overwintered as larva with another protracted peak of late larvae in June. Sometimes these early and late peaks persist which can appear to be additional generations but, more often, they merge. The late summer generation is usually double the size of 1st but this year it tripled in size benefitting greatly with the heat on the lowlands. After two years of decline it has certainly bounced back particularly on our woodland sites. This year we see a doubling in abundance compared to last year poor showing and up a quarter against the 5 yr average,
It is easy to forget what a late arrival Speckled Wood was in Yorkshire. We can see the first arrivals right in the south of the county with 2 sites in 2002. This was followed immediatly by huge surge in numbers by nearly double their now regular abundance, then, after 3-4 years it settles down. Currently everything above 300m altitude sites only get a stray or two but the 200m line was passed in 2010. Interstingly the diabolical summer of 2012 all 200m sites fell back to zero but quickly returned in 2013.
2022 was certainly a peak and since 2006 and the initial surge the increase in abundance is about 30% and 12% in the last 10 years
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.
The first generation is at the beginning of May and two weeks later on uplands. The 2nd generation is late July and is twice the size of the first but not this year which after a strong first generation the 2nd was similar which is remarkable considering how parched and brown most grasslands had became. A significant third brood occured along its strongholds on the coastal strip. Overall Wall showed a 25% increase in abundance following a very strong showing in 2021 and it long term prospects here is Yorkshire seem more stable. In contrast for many southern inland counties it is now extinct or just clinging on having been reclassified as 'endangered' in the new Red list. In Sweden this species is moving north and genetically evolving to hibernate in shorter days to avoid being too late to hibernate succesfully. The suicide generation theory seems now to be lacking real proof and perhaps now given some years to adapt we are seeing rapid change.
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.
Scotch Argus only has 1 monitored site but was very much up this year more than double the average but a tad down on last years peak.
The increase in abundance is 60% in last 4 years and continuing to rise fast.
Marbled White has had another remarkable year. It peaked early at the end of June with high numbers but fizzled out quickly in the heatwave. This butterfly can be prolific on unimproved calcareous grasslands and you can see multiple individual nectering on the same flower head. Yorkshire is at the northern edge of its range but it continues to spread. There was also a remarkable dispersal this year with individuals seen far ranging on grasslands even appearing in the authors garden which is surrounded by intensive farmland and 15 miles from another colony! This demonstrates this species ability to disperse over long distances and cannot be regarded as sedantery with specimens turning up in the middle of York.
Its range has limitations as this butterfly gains protection from birds by injesting and sequestering a toxic alkaloid from its food. This alkaloid is produced by a ergot like fungus and endoparasite of Red Fescue which is an important part of the larval diet. This fungus has a strong smell which the butterfly is thought to be able to detect and females do not bother to land but lay eggs as they fly. The toxin is stored in the wings and the black and white marbling is a warning to birds who quickly learn to avoid. Almost all our lowland grassland sites see wonderers each year but are likely rejected by females Marbled White by not 'smelling' correct for dropping eggs. The famous lepidopterist Miriam Rothschild who developed the meadow mix of seed species we use commonly today, which she refered to back then as 'Farmers Nightmare' as she tried in vane to attract the Marbled White to her home. It was only at the very end of her life she discovered the connection to the poison and ergot.
This species has had 3 years of consequetive increases and long term abundance is growing by 40% in the last 10 years similar to the national trend. It is no longer restricted to its strongholds on the Wolds with lots of new colonies on railway embankments and verges, old querries, brownfields and heaths in the Vale of York but also moving north along the limestone ridge and venturing well up the Don to Rotherham and Aire to Bradford but not the Wharfe which seems to mark its northern limit apart from the limestone ridge where we might expect it to colonise Nosterfield very soon.
Insufficient data for a long term trend.
Gatekeeper showed the second largest increase in abundance after Holly Blue, up 31% , and on top of the boom of last year and the third year of increase. It was seen on more of our monitored sites so signs of dispersal in addition. Numbers peaked in mid July but fell back rapidly after the heatwave and it was gone by mid August. Gains on sites were almost universal. Autumn 2021's dry November followed by a cool start to December worked in favour of low mortality in hibernation but then a warm dry June always 'sets up' our summer butterflies by reducing the period of the vunerable pupal stage.
Long term the trend has been down about 40% since 2004 (25% in the last decade) with a significant dip from 2015-18. From then on there has been a significant rise of 45% with the succession of good summers and dry warm springs, but is that about to change?
Meadow Brown our most common Butterfly peaked early in the first two weeks of July and showed a pretty consistant but 14% increase in abundance across our sites and the third year of increases. This year has seen many late emergences of females on limestone grassalnds which is consistant with later (mostly female) caterpillars forced to diapause for about a month in the heat and parched vegetation on thin limestones soils and fresh females were still being seen in mid September at Brockadale. There is only a small 1 week difference between the timing of upland and lowland sites this year. Thorpe Marsh as usual had the highest index
Long term meadow Brown shows a very small increase over the last 20 years but with a considerabel variation. 2003 was a very good year but numbers fell away and hit a low in 2009-12 and then rose very rapidly in the good summers of 2013-14 only to fall back and then boom once again in 2019 However its seems to be maintaining gains with a much steeper slope of increase of in excess of 60% over the last 10 years
Ringlet our second most common species was also early peaking in the first week of July while upland areas were a week later and all areas peaked and finished quickly after catching the brunt of the heatwave. There was a pretty consistant increase in abundance across our sites of 15% after 2 years of decreases and was 22% up on last year.
Ringlet has seen a huge increase in abundance over the last 20 years of over 100% and 35% in the last ten years althoug there are signs of passing a peak since 2015. On our monitored sites Ringlet has moved up in altitude to near 300m since the peak years 2013/14.
Small Heath is present 40 of our managed sites and remains common anywhere with unimproved grassalnds and brownfields. After a fantastic 2021 it held onto a good deal of the gains and has shown a consistant increase these last three years, although well down on last year. Long term trends nationally are pretty flat even though it has recently been reclassified from near threatened to vunerable due to the loss of many sites in the south of england this species being rather sensitive to nitrogen disposition. However nationally it has seen a significant increases recently although this has largely been in the northern UK with the species becoming extinct in some southern counties. Good lowland sites peak in mid May when upland sites are barely starting and is largely a single generation peaking a month later in mid July. By the beginning of August a smaller second generation begins to emerge but you can see that both upland and lowalnd are a mix of univoltine and bivoltine that gradually spreads out at lower altitudes to an increasing second generation,
Over the last twenty years there has been considerable ups and downs but they are pretty similar to other species namely with troughs in 2007-9 and 2016-7 and a clear run of quite good summers have allowed the species to have a sustained peak in 2021 . Overall abundance has increased by 65% in the last 20 years and 23% in the last Decade however the slope has changed as with ringlet sharply upwards since 2016 with 7 years of consistant rises and increasing the trend to 44% in the last ten years. Again will this continue or was 2022 the end of this run?
2021: A year with a record breaking cool spring created a big delay followed by a large peak in our summer species . Overall an average year
2020 A year with a record breaking early spring followed by a wet windy summer made for a mixed year
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 .
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
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
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.