Westcott, Bucks - the year 2023 in review

It was another year of mixed fortunes for lepidoptera in our garden at Westcott.  As far as overall numbers are concerned it was certainly a much better year than 2022 but diversity was down a little bit.  Despite 2023 going down officially as the UK’s second warmest year ever, spring-time temperatures locally weren’t brilliant and rainfall was higher than usual.  June was excellent all round, but overall the Summer weather was spoilt by a poor July.  Autumn was certainly warmer than usual but by then it was too late to have much of an effect on our butterflies and moths.          

Butterflies

The first butterfly sighting of 2023 in the garden was, as is often the case, a Brimstone Gonepteryx rhamni but I had to wait until 21st March for it which is later than most years, while the final sighting was of a Red Admiral Vanessa atalanta on 30th October.  A total of 20 adult butterfly species put in an appearance, slightly below the average.  However, the overall count of 927 individuals was only about 100 short of the average here and, thankfully, was significantly better than the dismal count in 2022.  Red Admiral had an excellent year everywhere and the garden was no exception, the overall count being just over 300 so making up a third of all garden sightings.

Red Admiral on privet blossom, Westcott 22nd June 2023

Holly Blue Celastrina argiolus also had a very good year with garden records on 47 dates between 4th May and 15th September.  65 individuals were seen altogether, which I think is a record here.  The highest counts for Holly Blue, both of four noted at the same time, occurred on 18th August and 4th September.  White-letter Hairstreak Satyrium w-album made almost daily appearances between 23rd June and 17th July with the peak count being four seen together on 6th July.  Yet again a visit from a female Brown Hairstreak Thecla betulae in late-August or early-September went unrecorded but she left a memento of her visit by laying a couple of eggs on our garden blackthorn.  The eggs were discovered on 8th September but unfortunately both had disappeared by the end of that month, presumably having been predated either by other insects or by the local tit population.

Small Tortoiseshell Aglais urticae had a very poor year indeed here with just 13 individuals seen.  Absentees from the garden during 2023 included Grizzled Skipper Pyrgus malvae, Small Copper Lycaena phlaes and Small Heath Coenonympha pamphilus, even though all three were seen in adjacent fields, while I failed to see Painted Lady Vanessa cardui anywhere in Bucks for the first time in more than 20 years.  

The Mothing Year

712 different moth species were recorded in the garden during 2023 (362 micros and 350 macros, the full list can be seen here on Google Sheets).  The overall moth count came to just under 35,000 individuals which wasn’t bad at all considering how disappointing the night-time weather was for much of what is normally the busiest month of July.  Two traps (either two actinic lights or else an actinic and MV) were run between 7th April and 18th November, with just a single actinic employed outside those dates.   The table below shows the year’s results with data from the previous nine seasons for comparison (Nights = number of nights when at least one trap was run; Micro & Macro = total number of species; Count = total number of individual moths).    

Year	Nights	Micro	Macro	Count
2014	259	293	307	32,910
2015	298	309	324	33,941
2016	289	316	315	26,697
2017	279	326	336	28,189
2018	286	346	338	42,063
2019	323	344	355	54,400
2020	320	345	330	36,784
2021	335	380	332	29,330
2022	326	383	360	38,146
2023	320	362	350	34,986

Looking at the three busiest months of the year, the highest combined moth count from the two traps in June was 777 individuals on the 28th, while in July it was 684 on the 7th and in August was 494 on the 9th, so definitely no records broken there.  As far as species are concerned, there were counts of 100 species or more on 17 nights over those same three months (one fewer than in 2022).  Eleven of them occurred during June with 131 species on the 28th being the highest.  There was a very disappointing count of four such nights in July (150 on the 7th being the highest), while two more followed on consecutive nights in August (104 on the 9th and 114 on the 10th).

The best performing moth of 2023 proved to be Large Yellow Underwing Noctua pronuba with 2,055 individuals.  Only three species produced more than a thousand individuals during the year, the other two being Dark Arches Apamea monoglypha (1,804) and the grass moth Chrysoteuchia culmella (1,159).  

Newcomers to the garden list during 2023 comprised 13 species (11 micros and 2 macros).  This was only half of the previous year’s total, but after 20 years trapping at this site I find it amazing that even this many new ones still turn up.  The combined lepidoptera total for the garden (butterflies as well as moths) has now passed 1,100 species.

  

12.021	Nemapogon clematella	10 Jun
12.047	Psychoides verhuella *	24 Jun
32.039	Depressaria daucella *	16 Apr
32.045	Bryotropha basaltinella *	6 Sep
35.077	Monochroa hornigi *	7 Jul
35.107	Psoricoptera gibbosella *	31 Jul
45.039	Hellinsia carphodactyla *	2 Sep
49.016	Archips rosana *	21 Jun
49.364	Pammene suspectana *  (to MOL lure)	18 May
62.013	Uncinus obductella *	29 Jul
63.119	Musotima nitidalis	19 Oct
73.105	Bird’s Wing  Dypterygia scabriuscula	28 Jun
73.365	Autumnal Rustic  Eugnorisma glareosa	3 Oct

* confirmed via dissection, with grateful thanks to Peter Hall.

Micro-moths

The majority of the newcomers were, as usual, micro-moths.  Perhaps the most interesting amongst them was the tortrix Pammene suspectana which was a daytime record, appearing at the MOL pheromone lure within a minute of hanging it out at 4pm on 18th May.  The moth was clearly either Pammene albuginana or suspectana, either of which would have been new for the garden list, but dissection proved it to be suspectana which also happened to be a first for Bucks.  Although as yet unconfirmed, the moth’s larvae are believed to be associated with the bark of Ash Fraxinus excelsior.  There are plenty of Ash trees around here and the lure was actually suspended below one, perhaps explaining the prompt arrival of this individual.  Like Pammene giganteana, it was thought to be very uncommon until recent use of these lures suggested otherwise. 

Pammene suspectana, Westcott 18th May 2023

Of the other micros, gelechiid Monochroa hornigi was a first for the county, while tortrix Archips rosana had the distinction of being only the second example I’ve ever seen in Bucks (the other being at Dancersend in 2019) and it seems to be genuinely scarce hereabouts.  The pyrale Uncinus obductella used to be confined to Kent but now seems to be spreading quite rapidly.  Its larvae feed on marjoram and over the last few years I’ve found it in numbers at Grangelands and at Yoesden Bank so it seems to be quite well established on some of our better chalk grassland sites in the Chilterns.  Musotima nitidalis is another spreading species, this time a fern-feeding adventive from the Antipodes which was first recorded in the UK during 2009 and has been known from Bucks only since 2020. 

Uncinus obductella, Westcott 29th July 2023

Musotima nitidalis, Westcott 19th October 2023

Most micro species seen in the garden during 2023 were within the normal variation in numbers to be expected here from year to year.  It was good to have Triaxomasia caprimulgella to the LUN pheromone lure for the second year running (two examples on 29th June).  Sorhagenia rhamniella (7th July) was only the third garden record of that species yet we have had both of its larval food-plants (buckthorn and alder buckthorn) in the garden for many years so it is surprising that it doesn’t appear more frequently.  Spilonota laricana (28th June) was the first record here since 2008, while Dichrorampha simpliciana (9th July) was making its first appearance here for 17 years.  Just about the only noticeable decline during the year was that of Blastobasis adustella which was down from 262 individuals in 2022 to just eight in 2023.    

 

Macro-moths

Only two macro-moth species were new for the site in 2023, but neither one was expected here which made them that much more welcome.  Although there have been a handful of past records in the area around Milton Keynes, in Bucks the Bird’s Wing is generally limited to the southern half of the county.  My area towards the north-west has no previous records at all, so the visitor on 28th June was presumably a wanderer.  Autumnal Rustic is one of the smartest of the late-season noctuids and is also largely absent from this area of the county, although I did get a surprise in Bernwood Forest  in September 2021 when one turned up to a light trap there so maybe it is spreading into the area.  

Bird's Wing, Westcott 28th June 2023

Autumnal Rustic, Westcott 3rd October 2023

Amongst the macro-moths putting in their best ever counts here during the year were Least Carpet Idaea rusticata (136), Scalloped Oak Crocallis elinguaria (102), Feathered Thorn Colotois pennaria (149), Willow Beauty Peribatodes rhomboidaria (529), Burnished Brass Diachrysia chrysitis (105), Nut-tree Tussock Colocasia coryli (78), Webb’s Wainscot Globia sparganii (25), Centre-barred Sallow Atethmia centrago (324), White-point Mythimna albipuncta (506) & Heart & Club Agrotis clavis (208).  Twin-spot Carpet Mesotype didymata was good to see again after its last visit in 2013, although the specimen which turned up on 4th July needed dissection to confirm its identity because it was so badly worn.  It was also very nice to get repeat visits from True Lover’s Knot Lycophotia porphyrea on 29th June (the first since 2017), a rather worn Square-spotted Clay Xestia stigmatica on 13th August (there is only one previous record here from ten years earlier) & Cream-bordered Green Pea Earias clorana which appeared on both 16th June and 10th July (only one previous garden sighting from back in 2018).  Notable absentees during the year included Ghost Moth Hepialus humuli, Peach Blossom Thyatira batis, Large Twin-spot Carpet Xanthorhoe quadrifasiata, Ear Moth Amphipoea oculea & Dusky Brocade Apamea remissa although I suspect they’ll bounce back in 2024.

True Lover's Knot, Westcott 29th June 2023

Square-spotted Clay, Westcott 13th August 2023

Cream-bordered Green Pea, 16th June 2023

The last review of the status of the UK’s macro-moths using International Union for Conservation of Nature (IUCN) “Red List” criteria took place in 2019 and since then they have been labelled (in order of status) Regionally Extinct, Critically Endangered, Endangered, Vulnerable, Near Threatened or of Least Concern.  It stands to reason that the majority of macro-moths recorded at Westcott fall under the Least Concern category, but during 2023 there were several with enhanced status and they are tabulated below (including their numbers seen during the year):

Endangered	Lappet	1
	Maple Pug	11
	Figure of Eight	29
Vulnerable	Oak Hook-tip	4
	Pale Eggar	6
	Lackey	105
	Pale Brindled Beauty	82
	Mottled Umber	95
	Early Moth	12
	Mouse Moth	13
	Sprawler	175
	True Lover’s Knot	1
Near Threatened	Frosted Green	1
	Toadflax Pug	2
	White-spotted Pug	27
	Grey Pug	5
	Dusky Thorn	64
	September Thorn	16
	Garden Tiger	2
	Blackneck	6
	Large Nutmeg	72
	Sallow	33
	Dusky-lemon Sallow	3
	Beaded Chestnut	327
	Minor Shoulder-knot	8
	Broad-barred White	1
	Double Dart	1
	Autumnal Rustic	1

Of those classed as Endangered, all three are regular visitors here.  Lappet numbers vary but I’m pleased to say that the moth appears most years in single digits.  Maple Pug is more frequent with annual numbers in the teens, while Figure of Eight has appeared annually over the past 20 years in varying numbers but has actually been on the increase since first achieving a double-digit count in 2018.    

Lappet, Westcott 22nd June 2023

Migrant moths

Far fewer migrant moth species made it to Westcott in 2023 than did during 2022 but there was still some interest, in particular from Vestal Rhodometra sacraria and Delicate Mythimna vittelina which, unusually, were around in considerable numbers during the year.  However, the best garden visitor was undoubtedly the Beautiful Marbled Eublemma purpurina on 5th September.  This was the second occasion that one of these smart moths has found its way to Westcott. 

Species	Total	First	Last
Plutella xylostella	19	10 Jun	5 Sep
Udea ferrugalis	19	21 Jun	20 Nov
Nomophila noctuella	1	14 Aug	-
Hummingbird Hawk-moth	26	26 Jun	20 Aug
Vestal	8	19 Aug	11 Oct
Beautiful Marbled	1	5 Sep	-
Four-spotted Footman	1	5 Sep	-
Silver Y	158	8 May	19 Oct
Delicate	15	25 Jun	17 Oct
Dark Sword-grass	12	11 Apr	22 Nov

Beautiful Marbled, Westcott 5th September 2023