Countywide, a bumper year that could not have been more opposite to 2024. Butterflies were seen, and flight conditions achieved, almost every day from March through to August. Butterflies boomed in the warmest  and sunniest Spring and Summer on record. Sometimes they were seen in clouds, mostly Large and Green Veined whites, either as migrants coming in from the sea along our east coast or in sheltered flowery places where they accumulated in huge numbers. Other species were behaving similarly with clouds of Speckled Wood and even an observation of a cloud of Purple Hairstreak above a tree. Yes, butterflies were swarming, a prelude and postlude to migration and dispersal and this year’s records clearly show this; they were on the move! So,it is no coincidence that it was the best year this century for Clouded Yellow. It wasn't just the sheer numbers, almost every species was absurdly early, averaging two weeks early! By the end of April abundance was already up 50%  with record counts of Peacock, Speckled Wood and Brimstone, with some transects recording  over 100 insects each week; remarkable as these were summer time numbers but we were still in April! An amazing 22 species were on the wing  by the end of that month, which is double twenty years ago and 30 species by the end of May with both Marble White and Silver-washed Fritillary had started to emerge. We had never seen a year like this! 

 It was also the driest year in a century. By early June plant growth slowed, lawns rarely needed a cut, soils cracked, crops wilted, verges went brown and no hay crops as grasslands were so short and sparse. There were consequences and the boom was certainly not universal with many doing exceptionally well while others were well below par. On thin soils the grass feeding ‘Browns’ which make up the majority of our summer species fared particularly poorly and in fact at Wharram Quarry, with almost no soil, numbers were lower than in 2024 as they were on Inglebrough’s Limestone pavements!  This was contrasted with the damp, deep moist soils in the river valleys where those  same brown species were booming particularly in part shade of our woodlands and hedgerows. 50% of our sites were up more than 40% and more than double last year’s total. The Blues and Small Copper bounced back from last year's disaster and boomed on the warm thin sparse swards. Small Copper earned its place as ‘species of the year’ by having not only its best year on record with an enormous third brood; 33 times higher than last year, which happened to be a record low. The exceptions were the Small Heath only managed to struggle back to average while the Small Tortoiseshell after a great start, and quite a good first generation the heat and drought caused them to go straight into hibernation and few were seen after mid June except in cooler/damper locations and is forced to higher altitudes to escape.Overall the year was up 30% against the 5 year average and has beat every year since the millennium! For 20 of our species this was either their best or second best year on record. Large White, Brown Argus,Dingy Skipper and Speckled Wood had their best year.

Countywide, after a warm winter  April turned  cold, very wet and dull and everything just about stopped and it was near impossible to transect walk all month. By May  there were already  losses  among our spring species being  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.  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 but 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 a blip