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 |
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 |
