Westcott, Bucks - the year 2024 in review

This was a poor year for lepidoptera at Westcott.  The number of species seen, as well as total counts of individual butterflies and moths, were far lower than expected.  February, March and April brought much higher rainfall than normal and there was widespread flooding locally (including in the garden here) which seemed to last for ages.  Somewhat better weather later in the year didn’t seem to make a great deal of difference as the damage to early stages had presumably already been done.

Butterflies
 
The first butterfly sighting of 2024 in the garden was a Peacock Aglais io on 3rd February and the last was a Red Admiral Vanessa atalanta on 17th October, that’s discounting a Peacock found flying around indoors on 25th November which had presumably been disturbed from hibernation.  Only 17 species were recorded during the season, the lowest count here for 20 years, and one of those (Painted Lady Vanessa cardui) was a very last-minute sighting on 3rd October when a pair appeared briefly on our ivy blossom.  Numbers of individual butterflies were also the lowest ever at just 304, the largest contribution to that total being provided by Red Admiral with 68.  Then came Holly Blue Celastrina argiolus with 35, Peacock also 35, Gatekeeper Pyronia tithonus 32 and Brimstone Gonepteryx rhamni 24, while at the other end of the scale Marbled White Melanargia galathea and Small Tortoiseshell Aglais urticae tied for the lowest with just one sighting of each.  All very disappointing indeed.
 
There were no records at all of Large Skipper Ochlodes Sylvanus or Common Blue Polyommatus icarus, both of which usually turn up in small numbers, while White-letter Hairstreak Satyrium w-album became an absentee for the first time since 2013 following the demise of our final Elm to Dutch Elm Disease.  The floods early in the year are assumed to have been the cause of the demise of some other garden trees and shrubs, including mature examples of Cherry and Holly as well as one of our Buddleias.  It will be interesting to see if the loss of the Holly has any effect on Holly Blue numbers next year.      
 
The Mothing Year
 
Much the same as in the previous year, a twin-30w actinic light was run inside the conservatory from 1st January until 29th March 2024, with any visiting moths being potted up from the windows.  From 30th March onwards two traps were employed out in the garden, both of them initially being twin-30w actinic Robinsons until one was replaced by a 125w MV Robinson at the beginning of May.  As the season drew to a close the MV was replaced by the second twin-30w once again from the end of September until I reverted to “winter operations” with a single light back inside the conservatory from 17th November.  There were 12 occasions in January when it wasn’t worth turning on the lights because the temperature had dropped below freezing well before dusk, but otherwise they were run every night throughout the year apart from when we were away.  The only nil returns recorded were during January (3), November (4) and December (6).

682 different moth species were identified in the garden during 2024 (351 micros and 331 macros).  The overall moth count came to just over 26,000 which is the lowest total for more than a decade.  The table below shows the year’s results, accompanied by data from the previous nine seasons for comparison:    
 

Year	Nights trap was run	Micro species	Macro species	Overall moth count
2015	298	309	324	33,940
2016	289	316	315	26,695
2017	279	326	336	28,189
2018	286	346	338	42,063
2019	323	344	355	54,400
2020	320	345	330	37,186
2021	335	380	332	29,329
2022	326	383	360	38,145
2023	320	362	350	34,989
2024	340	351	331	26,270

 
Looking at the three busiest months of the year, both June and August were poor for species numbers while July (when I was away for the first ten days) proved to be somewhat better but was still below average.  Counts of 100+ species in a single night were achieved on only nine occasions, three of them in late-June, four in July and the other two in the first half of August.  The best night for species was 30th July when 145 were recorded (667 moths in total). 
 
The best performing moth of 2024 proved once again to be Large Yellow Underwing Noctua pronuba but with a count of 1,279 (down from 2,055 in 2023) and this was the only species to exceed a thousand individuals during the year.   
 
Thankfully, to keep the interest going in an otherwise poor year, there were 16 newcomers to the garden list (eleven micros and five macros), which was actually two more than in 2023.  I feel very grateful to be getting any new species at all after more than 20 years of recording at this site:
 

4.014	Stigmella catharticella (leaf-mine)	18 Aug
4.079	Zimmermannia atrifrontella *	5 Sep
12.040	Monopis imella *	31 Jul
15.057	Phyllonorycter dubitella *	31 Aug
15.0905	Phyllocnistis asiatica *	23 Jun
16.003	Yponomeuta malinellus	24 May
16.024	Ocnerostoma friesei *	8 May
28.013	Crassa tinctella	14 May
29.002	Diurnea lipsiella	9 Nov
37.098	Coleophora inulae *	2 Aug
49.053	Cnephasia pumicana *	29 Jul
65.0021	Spiny Hook-tip Watsonalla uncinula *	1 Nov
72.057	Plumed Fan-foot Pechipogo plumigeralis *	10 Aug
73.053	Chamomile Shark Cucullia chamomillae	14 Apr
73.128	Saltern Ear Amphipoea fucosa *	24 Jul
73.347	Langmaid’s Yellow U’wing Noctua janthina *	22 Oct

* confirmed via dissection, with grateful thanks to Peter Hall
 
Micro-moths
 
Yponomeuta malinellus has at last been confirmed from Westcott.  A small web of larvae was taken into custody from our domestic apple on 24th May and reared indoors, the first adult emerging on 20th June.  It joins Yponomeuta cagnagella (which uses spindle) on the garden list, leaving Yponomeuta padella (which uses blackthorn) as the only outstanding species of the three which can’t be separated as adults.  The first signs of anything using our garden buckthorn Rhamnus cathartica appeared on 18th August when I noticed one vacated leaf-mine of Stigmella catharticella which is a moth specific to that plant.  Another vacated mine from the same species was found on it about ten days later so next year’s task will be to try and find an active mine with the larva still present.  The shrub must be ten years old by now so it is about time something was found on it.  Mind you, we have a much larger bush of alder buckthorn Frangula alnus on the other side of the garden, searches of which have only ever produced the occasional caterpillar of the Brimstone butterfly. 

Yponomeuta malinellus (reared), Westcott 20th June 2024

Mine of Stigmella catharticella, Westcott 18th August 2024

The remainder of the newcomers to the garden during 2024 were adult moths which came to one of the light traps.  Particularly noteworthy amongst them were Zimmermannia atrifrontella (5th September) which as a larva mines the bark of younger stems on oak Quercus robur.  There are few records for Bucks, most of them being from Bernwood Forest and Burnham Beeches, but it is probably under-recorded because the mines are indistinguishable from those of Z.longicaudella and the tiny adult moth also requires dissection to get to species.  Monopis imella (31st July) is one of the more obscurely marked members of that family which are often associated with detritus in bird’s nests.  It is Nationally Scarce with only a couple of previous records from the south of the county, so a very nice sighting here in the garden.  In 2024 I kept back all examples of “Phyllocnistis saligna” (associated with willows) which is a relatively common visitor to the traps here between June and August each year.  Their retention was necessary because of the recent discovery in the UK of a confusion species, Phyllocnistis asiatica.  Of 13 individuals retained from Westcott, six were females and confirmed as the new species, while the other seven were males which can’t be distinguished by dissection although it seems fairly probable that they too will have been P.asiatica.  Until someone manages to confirm a specimen of Phyllocnistis saligna by dissection (if female) or via DNA sequencing then all previous records of this species in our area are thrown into doubt.               

Phyllocnistis asiatica, Westcott 23rd June 2024

Another Nationally Scarce species, Coleophora inulae was an unexpected moth for the garden and becomes the 47th Coleophoriid to have been found at Westcott, almost all of them confirmed by dissection.  This one could well be under-recorded locally because its larvae are associated with common fleabane Pulicaria dysenterica and ploughman’s spikenard Inula conyzae, of which the former at least is quite common in the damper areas of this part of Bucks.   The other newcomers to the garden list were of reasonably widespread species which would have found their way here sooner or later.  Amongst them the most welcome was Diurnea lipsiella (9th November), which flies only at the end of the year, thus providing a bit of excitement when the season was regarded as almost over.  

Diurnea fagella, Westcott 9th November 2024

Macro-moths

There were five new macro-moths for the site in 2024, the first to arrive being Chamomile Shark which turned up to the twin-30wt actinic light on 14th April.  The “Sharks” in general (all British Cucullia moths) are quite well known for being reluctant to come to light traps so in 2023 I acquired a pheromone lure for this particular species because it should be fairly widespread locally and there had been a larval find in a field margin near Finemere Wood, not too far from here, back in 2015 by the late Dave Maunder.  This was my first opportunity to use the lure at the correct time of year so I placed it out adjacent to one of the traps for seven nights from 7th April.  The pheromone brought in nothing at all but then, on the first night after I’d decided to give it a break and placed the lure back in the freezer, a single male of the target species came to the light trap!  I’m sure there must have been some chemical residue remaining on adjacent vegetation.

Chamomile Shark, Westcott 14th April 2024

I had to wait until 24th July for the next potential new macro species to turn up and that was an odd-looking Ear species.  I had a feeling that it might prove to be a wandering Saltern Ear Amphipoea fucosa rather than the usual Ear Moth Amphipoea oculea which is the only species known to be resident in Bucks, and so it proved to be when eventually dissected by Peter Hall during January 2025, the first record of Saltern Ear for VC24.  The moth is well established in coastal areas of East Anglia, around the Thames Estuary and into Kent, as well as along the south coast from Hampshire westwards, so could have wandered in from any of those areas.  A rather battered male Plumed Fan-foot came to the MV trap on 10th August, another addition to the site list, and a female was disturbed in the garden during the daytime on 8th October so it looks as though this spreading species may be in the process of becoming established locally. 

Saltern Ear, Westcott 24th July 2024

Plumed Fan-foot, Westcott 10th August 2024

On 16th October one of the actinic traps brought in a late example of what I assumed to be Lesser Broad-bordered Yellow Underwing Noctua janthe, this being a good five weeks after my last sighting of the species in the garden.  Another one on 22nd October got me wondering if these might actually be something more interesting so I retained the second moth and, when eventually dissected, it proved to be Langmaid’s Yellow Underwing Noctua janthina, another first for Bucks.  Unusually, I failed to photograph it before it was placed in the freezer, but Peter Hall managed to salvage the important elements which are recorded in his dissection image below.  I also now wish I’d retained the example from 16th October as well!  N.janthe and N.janthina are supposed to be distinguishable with reference to their hind-wings but from what I’ve seen this can be rather open to interpretation and may not work in all cases anyway, so is not a method of identification anyone unfamiliar with the species should be using.  Dissection of suspected candidates for janthina is the way forward.

Langmaid's Yellow Underwing, Westcott 22nd October 2024

The final macro-moth added to the garden list in 2024 was Spiny Hook-tip, another first for the county confirmed thanks to dissection by Peter Hall.  The moth turned up at Westcott on 1st November, some weeks after the last appearance of look-alike Oak Hook-tip Watsonalla binaria whose second brood was noted in the garden between 27th August and 15th September (18 individuals, six of which had their genitalia checked to confirm they were indeed that species).  Spiny Hook-tip is another moth, much like Phyllocnistis asiatica mentioned earlier, which has only recently been discovered “hiding in plain sight” in the UK.  In Europe its larvae feed on holm oak Quercus ilex but whether or not it breeds here or is just a migrant remains unclear.  Little is known yet about its distribution other than that the area around Bristol seems to be a hot-spot for the moth.  The first record for Berkshire (from Windsor) was confirmed a week after the Westcott specimen.

Spiny Hook-tip, Westcott 1st November 2024

Absentees from the garden during 2024, of moths which are pretty much guaranteed to appear annually, included Peach Blossom Thyatira batis (for the second year running), Hummingbird Hawk-moth Macroglossum stellatarum (its first ever absence in more than 20 years), Large Emerald Geometra papilionaria, Plain Golden Y Autographa jota, Large Wainscot Rhizedra lutosa, Dotted Chestnut Conistra rubiginea, Shears Hada plebeja and Cabbage Moth Mamestra brassicae.  Of the moths which usually visit in very high numbers, Heart and Dart Agrotis exclamationis (110) put in its worst performance ever and Dark Arches Apamea monoglypha (411) didn’t do well either.  Square-spot Rustic Xestia xanthographa (529) and Setaceous Hebrew Character Xestia c-nigrum (684) also achieved below-average counts.

However, even in a poor year there are usually some positive things and it is worth recording that the following species had their best ever annual counts in the garden:  Calamatropha paludella (53), Single-dotted Wave Idaea dimidiata (183), Cypress Carpet Thera cupressata (43), Blue-bordered Carpet Plemyria rubiginata (20), Oak-tree Pug Eupithecia dodoneata (29), Magpie Moth Abraxas grossulariata (135), Brindled Beauty Lycia hirtaria (42), Scarce Umber Agriopis aurantiaria (40), Gypsy Moth Lymantria dispar (44), Jersey Tiger Euplagia quadripunctaria (71) and Early Grey Xylocampa areola (22).  Furthermore, Hebrew Character Orthosia gothica (631) and Small Square-spot Diarsia rubi (581) each had their second best ever counts, the latter species being particularly susceptible to swings between boom and bust.  The three macro-moths given the IUCN designation “Endangered” in 2019 which visit the garden regularly (see last year’s report) did so again in 2024 in reasonable numbers and don’t seem to be under any particular threat locally.  Their counts for the year were as follows:  Lappet Gastropacha quercifolia (3), Maple Pug Eupithecia inturbata (20) and Figure of Eight Diloba caeruleocephala (27). 

Migrant moths

This was a fairly average year for migrants at Westcott, as shown in the table below.  Palpita vitrealis appeared in far greater numbers than it has ever done previously and many other recorders in Bucks will have seen it during the “migrant season” because there was quite an invasion this year.  I’ve included Spiny Hook-tip here but we don’t actually know for sure if this was a migrant (see earlier) although the time of year suggests that it may have been.  Like White-point Mythimna albipuncta, it seems that Delicate Mythimna vitellina may now be in the process of establishing itself as a resident locally so that moth may not feature in these tables for much longer. 

Species	Total	First	Last
Plutella xylostella	17	26 Mar	4 Dec
Udea ferrugalis	10	23 Aug	1 Dec
Palpita vitrealis	8	5 Sept	10 Nov
Nomophila noctuella	2	6 Sept	29 Oct
Spiny Hook-tip	1	1 Nov	-
Silver Y	62	1 May	16 Nov
Scarce Bordered Straw	1	7 Oct	-
Small Mottled Willow	1	5 Sept	-
Delicate	32	29 Jun	29 Oct
Pearly Underwing	1	29 Oct	-
Dark Sword-grass	15	15 Apr	15 Nov

Palpita vitrealis, Westcott 14th October 2024