Westcott, Bucks - the year 2020 in review

 

This was a strange year thanks to the COVID virus but it didn’t stop butterflies and moths from visiting Westcott and the first lock-down also gave me the opportunity to add a few more species from other insect orders to the garden list.  Many people seemed to think that, overall, the numbers of moths in particular were significantly lower than expected in 2020 but I didn’t find that to be the case.  Yes, the counts were down on those for 2018 and 2019 but then those were two exceptional years here and 2020 was much closer to the norm.            
 
Butterflies
 
The butterfly species count for the garden at Westcott in 2020 came to 22 which is the average figure for here (the lowest was 18 in 2008 and the highest 25 in 2013, from 31 different species recorded since the millennium).  The year’s first sighting came quite late, a Comma Polygonia c-album on 11th March, while the last was a Red Admiral Vanessa atalanta on ivy blossom on 25th September which did seem rather early for the season to end.
 

Orange-tip female, Westcott 23rd April

Holly Blue, Westcott 9th April

Of the early species, Orange-tip Anthocharis cardamines did well, as did Holly Blue Celastrina argiolus.  The latter appeared regularly in both April and May then again just as often in July and August.  Our garden colony of White-letter Hairstreak Satyrium w-album continued to thrive despite the ever dwindling supply of elm and was seen to be active between 16th June and 12th July with a maximum of two seen at any one time.   
 
There were some notable absentees during the year, with no sign at all of Small Skipper Thymelicus sylvestris, Small Copper Lycaena phlaeas or Common Blue Polyommatus icarus which are usually annual visitors - although all three were seen in the immediate local area - while Ringlet Aphantopus hyperantus was only recorded the once.  However, appearances by Grizzled Skipper Pyrgus malvae, Brown Hairstreak Thecla betulae and Silver-washed Fritillary Argynnis paphia made up for those absences.  Grizzled Skipper is found in a field about 60 metres away on the opposite side of one of our neighbouring properties, where it lives alongside Dingy Skipper Erynnis tages.  The example on 30th May was only the third ever Grizzled to have been found in the garden after singletons in 2011 and 2019, while Dingy has not yet been recorded here at all, which is rather disappointing considering how close the local colonies are.  A male Brown Hairstreak was seen to carry out a low-level transit of the back lawn on 7th August.  I couldn’t work out what it was until it paused very briefly on the grass and its identity became clear.  This was the first adult recorded here since 2014, but on 18th September I found four freshly-laid eggs on our blackthorn which means that a female must also have passed through unobserved.  A Silver-washed Fritillary made two welcome appearances on our buddleia a few days apart, on 19th and 22nd July.
 
The vanessids peaked at their usual times, Peacock Aglais io earlier than the others on 18th July when 16 were seen together, while the highest counts for Small Tortoiseshell Aglais urticae and Red Admiral came on 17th August (11) and 18th August (7) respectively.  None of those totals broke any records here and the migrant Painted Lady Vanessa cardui had a very poor showing with only the one sighting on 22nd August.  
 
The Mothing Year
 
While the overall garden moth count was down significantly on 2018 and 2019, those were actually two exceptional years and the final total of just over 37,000 individuals for 2020 was better than in 2017 or any earlier year here.  That would have been thanks in part to the need to stay at home due to COVID because the two garden traps were run together more often than in past years so there was actually an increase in trapping effort.  The 125wt MV and twin-30wt actinic traps were run in tandem on 174 occasions with the actinic being run on its own on a further 140 occasions, this being almost a complete reverse of the figures for 2019.  However, less than optimum weather conditions at times during the busiest period for moths (mid-June to mid-August) meant that 100 or more species in a single night was achieved on only 11 occasions as compared to 19 in 2019 and 26 in 2018.  The highest nightly species count was 134, reached on both 25th June and 11th August, and on both those occasions the MV trap managed more than 100 on its own.  However, the highest nightly count of individual moths (1,020) occurred on 16th July when the species count came to only 114.     

The two traps in their usual spots, Westcott 10th April

Lunar Underwing Omphaloscelis lunosa (2,758) achieved the highest count for an individual species in 2020.  That total was accumulated over a far shorter flight period than the other high-scoring noctuids, which comprised Heart and Dart Agrotis exclamationis (1,509), Large Yellow Underwing Noctua pronuba (1,351), Common Wainscot Mythimna pallens (1,297, its highest ever annual count here), Square-spot Rustic Xestia xanthographa (1,180) and Dark Arches Apamea monoglypha (982).  Common Footman Eilema lurideola also produced its highest ever count (1,260), as did Scarce Footman Eilema complana (651).  The highest micro totals were achieved as usual to the grass moths Chrysoteuchia culmella and Agriphila tristella.  The top 20 species for 2020 by overall count are tabulated below:

1	Lunar Underwing	2,758
2	Chrysoteuchia culmella	1,591
3	Heart and Dart	1,509
4	Large Yellow Underwing	1,351
5	Common Wainscot	1,297
6	Common Footman	1,260
7	Square-spot Rustic	1,180
8	Agriphila tristella	1,082
9	Acentria ephemerella	1,007
10	Dark Arches	982
11	Scarce Footman	651
12	Treble Lines	639
13	Setaceous Hebrew Character	632
14	Brimstone Moth	622
15	Vine’s Rustic	493
16	Flounced Rustic	450
17	Black Rustic	394
18	Agriphila straminella	389
19	Beaded Chestnut	355
20	Smoky Wainscot	346

Of the aggregated species which mostly require dissection to separate, Common Rustic Mesapamea secalis, Uncertain Hoplodrina octogenaria and Rustic Hoplodrina blanda would certainly have gained a place somewhere in the top 20 if they had all been identified to species, even though their totals were only half those achieved in 2019.
 

1	Uncertain/Rustic (Hoplodrina species)	1,324
2	Common/Lesser Common Rustic (Mesapamea species)	715
3	Minors (Oligia species)	247

However, with a total of only 247 individuals the Oligia species (Marbled Minor, Tawny Marbled Minor & Rufous Minor) were down on the numbers achieved over the last few years.  Other moths which put in a poor showing during 2020 included Clouded Silver Lomographa temerata (equal lowest count at 41, the annual average being 108), Clouded Drab Orthosia incerta (second lowest count at 83, annual average 190) and, most noticeably, Flame Shoulder Ochropleura plecta (lowest ever count at 90, annual average 435). 
 
After all necessary dissections had been completed the garden species count for 2020 came to 676 (346 micros and 330 macros) which is a more than acceptable tally.  The full species list for the year can be seen on a Google Sheets spreadsheet here.  In line with the number of individual moths mentioned earlier, that species score is the third highest ever achieved here and is the seventh year in a row in which more than 600 have been recorded.  As detailed in the table below, 19 of them were completely new for the garden list, taking the site total up to 1,020 moth species (574 micros and 446 macros).

4.054	Stigmella perpygmaeella (mine on hawthorn)	11th October
4.060	Stigmella ruficapitella *	24th July
15.017	Calybites phasianipennella *	22nd July
15.030	Parornix scoticella (mine on apple)	15th October
15.036	Phyllonorycter heegeriella (mine on oak)	24th August
15.065	Phyllonorycter esperella (mine on hornbeam)	5th September
16.004	Yponomeuta cagnagella (larvae on spindle)	25th April
32.030	Agonopterix nervosa	26th August
35.003	Aproaerema larseniella *	25th June
35.098	Gelechia scotinella *	31st July
38.045	Elachista utonella *	6th August
49.233	Epinotia solandriana *	21st July
49.245	Epinotia tetraquetrana *	25th May
49.305	Rhyacionia buoliana *	12th June
49.373	Pammene spiniana *	24th August
52.003	Lunar Hornet Moth (to pheromone lure)	11th July
63.005	Pyrausta despicata	12th August
73.059	Toadflax Brocade	8th August
73.304	Cosmopolitan *	19th August

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

Micro-moths
 
Five micro species were added to the garden list in their pre-adult stages.  Four were leaf-mining larvae, of which Parornix scoticella was probably the most interesting even though it is supposedly a common species.  It was found on our apple as an active mine which was opened and the larva photographed.  What surprised me the most about this was that within 24 hours the very industrious caterpillar had managed to re-fold the leaf edge and seal it again with silk.
 

Parornix scoticella mine, Westcott 14th October

Parornix scoticella mine, same leaf 24 hours later

Over the years quite a few of those micro-moths whose early stages mine oak leaves have been confirmed here as adults after dissection.  However, they must have come from elsewhere because we’ve not had an oak tree either within or even close to the garden until 2020 when a young sapling which had been growing in a pot for a few years was finally planted out.  During the summer it was very pleasing to find it being used straight away, with half a dozen Phyllonorycter-type mines being seen on 24th August.  Two of the mines were taken indoors to rear through and I suspected that they would turn out to be the very common Phyllonorycter harrisella which has been recorded here previously as an adult.  However, when the moths emerged on 10th September it was clear that they were actually the somewhat similar-looking Phyllonorycter heegeriella which was completely new for the garden list.
 

Phyllonorycter heegeriella, Westcott 10th September

Oak sapling, Westcott 10th September

Having found a vacated mine on our apple the previous year, I made more of an effort to look for occupied mines of the nepticulid Bohemannia pulverosella at the right time during  2020 and managed to locate this active one on the tree on 23rd June.
 

Bohemannia pulverosella mine, Westcott 23rd June

Coleophora lineola has been found fairly regularly amongst the many adult coleophorids from the light trap which I keep back for dissection each year.  Its larvae feed on Hedge Woundwort Stachys sylvatica, of which we have quite a lot in the garden, and this year I managed to locate some active larval cases on the plants including the one illustrated below.
 

Coleophora lineola case, Westcott 1st May

Yponomeuta cagnagella is the first to be confirmed from the garden of that little group of Ermine moths which can’t be separated as adults.  It is the only one of four almost identical species to feed on spindle and larval webs were found on our garden plants for the first time during April.  Some of the larvae were taken into custody indoors on 16th May and they pupated between 29th May and 4th June, the first adults emerging soon afterwards on 11th June.
 

Yponomeuta cagnagella larval web, Westcott 16th May

Yponomeuta cagnagella adult, Westcott 11th June

Of the other new species, a nice fresh example of Agonopterix nervosa visited the trap on 26th August.  There are only about 25 records for Bucks, mostly from the south of the county, so it doesn’t seem to be encountered all that often.   Aproaerema larseniella is a relatively common gelechiid moth of woodland across the county but this was the first of the three former Syncopacma species to have been found in the garden (and, based on habitat preferences, likely the only one that ever will be).  The nicely marked Elachista utonella was expected here one day and becomes the 14th member of that family to join the garden list.  Of the four tortricoid moths, the two uncommon Epinotia species were nice to see although I have previously found both of them in the local area.  It was also good to find Rhyacionia buoliana at long last amongst the other related pine-feeders which are regulars here.  However, Pammene spiniana was definitely the pièce de resistance because this was only the third record for VC24, the two previous ones having both come from the garden of Richard Ellis in the far south-east of the county.  I’ve often wondered why I don’t seem to get this blackthorn-feeding species because there’s so much of the food-plant around here.  It does seem to be genuinely ‘local’ in its distribution. At the time I failed to recognise the moth for what it was (and didn’t take a picture either) but kept it back for dissection as a “small dark tortrix” and, as is often the case for new moths here, it was Peter Hall’s skill with the microscope which confirmed its identity.
 

Agonopterix nervosa, Westcott 25th August

Aproaerema larseniella, Westcott 26th June

Elachista utonella, Westcott 8th August

Epinotia tetraquetrana, Westcott 25th May

 
Macro-moths
 
Three macro-moths were added to the garden list during 2020, the first of which was Lunar Hornet Moth Sesia bembeciformis.  At long last a pheromone lure for this species finally came onto the market in 2020 and proved to be very effective indeed.  When put out in the garden for the first time at 10.15am on 11th July two males turned up within fifteen minutes and I had similar success at a couple of other local sites too.  It was actually another very good year for the clearwing species in general, with pheromones bringing into the garden Red-tipped Synanthedon formicaeformis, Orange-tailed S.andrenaeformis, Red-belted S.myopaeformis and Currant Clearwing S.tipuliformis, meaning that only Yellow-legged S.vespiformis failed to appear from those which have been recorded here previously.  Although not in the garden I even had success with the lure for the rare Sallow Clearwing S.flaviventris at three sites in the local area during July so that has now become a possibility for here in future years.  However, once again the lure for Hornet Moth Sesia apiformis was tried on many occasions but the moth still refuses to come into the garden, even though on 28th May I found a vacated pupal case at the base of a black poplar less than 400m away.  I did get an adult male on 6th July in a poplar plantation some 5km away from home which at least served to confirm that the lure does work!

Lunar Hornet Moth, Westcott 11th July

Having captive-reared no larvae of Emperor Moth Saturnia pavonia the previous year because we were going to be away on holiday at a critical time during their development, in 2020 I tried out the pheromone lure for this species for the first time.  During the afternoon of 3rd April it brought two males into the garden within an hour so certainly seems to be quite effective.  However, on 15th April a female Emperor Moth came to the light trap and laid more than 100 eggs on the cartons.  Lockdown meant that those which weren't given away were successfully reared through to the pupal stage, thereby ensuring that I should once again have adult females to try "assembling" with next year.

Emperor Moth male on lure, Westcott 3rd April

Emperor Moth larvae emerging, Westcott 28th April

The other two macro-moths which were new for the garden list both arrived during August.  The first of them was Toadflax Brocade Calophasia lunula which, as a spreading species, had been on my “watch list” for a couple of years.  Just the one rather tired adult came to light on 8th August but a month later I found four larvae on Purple Toadflax Linaria purpurea growing out of the pavement beside our road less than 100m away from the garden, so hopefully further adults will appear here next year.
 

Toadflax Brocade, Westcott 8th August

Toadflax Brocade larva, Westcott 8th September

The third and final macro species added to the garden list was another rather tired-looking specimen, this time the second ever record for Bucks of the migrant Cosmopolitan Leucania loreyi after one caught by Martin Harvey in his Kimble garden during the autumn of 2017.
 

Cosmopolitan, Westcott 19th August

This fully-grown larva of Old Lady Mormo maura was found during the evening of 4th May feeding on a Portuguese Laurel Prunus lusitanica which grows up against our boundary fence.  The caterpillar showed little sign of being affected by the cyanide which this plant produces in its leaves and berries.
 

Old Lady caterpillar, Westcott 4th May

Old Lady had a good year as an adult too, with 13 individuals being recorded of which nine were to wine ropes.  From August onwards I put a little more effort than usual into this ancient method of attracting moths.  I had mislaid my “ropes” (some redundant curtain tie-backs) so for 2020 I used rolled-up tea-towels dunked into my home-made sugary red wine solution and hung from a tree in the front garden away from the lights at the rear.  Red Underwing Catocala nupta was another regular to the ropes.  The spectacular Clifden Nonpareil Catocala fraxini also responded to them, bringing in my first two visitors of the year from a total of eight individuals recorded in the garden during 2020.

Old Lady, Westcott 26th August

 

Red Underwing, Westcott 12th August

Clifden Nonpareil, Westcott 13th August

Quite a few macro-moth species put in their best ever annual performances here during the year and they included Orange Swift Triodia sylvina (105), Lackey Malacosoma neustria (125), Least Carpet Idaea rusticata (93), Common Pug Eupithecia vulgata (108), Willow Beauty Peribatodes rhomboidaria (247), Light Emerald Campaea margaritaria (232), Buff-tip Phalera bucephala (133), Tree-lichen Beauty Cryphia algae (97), Treble Lines Charanyca trigrammica (639), Rosy Rustic Hydraecia micacea (114), Flounced Rustic Luperina testacea (450), Deep-brown Dart Aporophyla lutulenta (263), White-point Mythimna albipuncta (146) and Lesser Yellow Underwing Noctua comes (238).
 
I was very pleased to get further records of the smart-looking Pinion-spotted Pug Eupithecia insigniata, a nationally scarce species which first appeared here in 2018.  Four individuals came to light over three consecutive nights during the second half of May.
 

Pinion-spotted Pug, Westcott 21st May

 
Amongst those moths which are fairly recent colonists and are expanding their range into our area, Cypress Pug Eupithecia phoeniceata and Oak Processionary Thaumetopoea processionea achieved similar numbers to 2019 (counts of 11 and 3 respectively), Jersey Tiger Euplagia quadripunctaria showed a slight increase (6) while there was a minor explosion in the numbers of Gypsy Moth Lymantria dispar (16, having only appeared as singletons in previous years).  Those visitors which made it here from the two “pest” species Oak Processionary and Gypsy Moth were as usual all males and I’ve yet to see the female of either species anywhere in Bucks.

Gypsy Moth, Westcott 4th August

As always there were disappointments too with several regulars failing to appear at all, including Grass Rivulet Perizoma albulata, Pale Oak Beauty Hypomecis punctinalis, Garden Tiger Arctia caja, Round-winged Muslin Thumatha senex, Sycamore Acronicta aceris, Large Wainscot Rhizedra lutosa, Mere Wainscot Photoedes fluxa and Dot Moth Melanchra persicariae.  I failed to get repeat visits from Dewick’s Plusia Macdunnoughia confusa or Oak Rustic Dryobota labecula after their first appearances in 2019 but, having made it here the once, they’re sure to do so again sometime in the future.
 
Migrant Moths
 
It was quite a good year for migratory moths at Westcott in that two of them (Pyrausta despicata and Cosmopolitan) were complete newcomers to the garden.  The appearance of three different migrant Hawk-moth species was also rather unexpected although one of them, Hummingbird Hawk-moth Macroglossum stellatarum, is of course a regular and did very well thanks to a buddleia right outside our kitchen window.  Silver Y Autographa gamma and Dark Sword-grass Agrotis ipsilon also visited in good numbers but the others had a somewhat disappointing season and one of them (Vestal Rhodometra sacraria) failed to appear at all for the first time in ten years.

 

Species	Total	First seen	Last seen
Plutella xylostella	12	24th June	17th November
Pyrausta despicata	2	12th August	14th August
Udea ferrugalis	16	12th August	23rd November
Nomophila noctuella	5	30th June	2nd September
Convolvulus Hawk-moth Agrius convolvuli	1	14th August	-
Silver-striped Hawk-moth Hippotion celerio	1	30th July	-
Hummingbird Hawk-moth Macroglossum stellatarum	54	6th July	23rd September
Dark Spectacle Abrostola tripasia	3	15th June	14th September
Silver Y Autographa gamma	226	6th May	2nd December
Cosmopolitan Leucania loreyi	1	19th August	-
Pearly Underwing Peridroma saucia	1	31st October	-
Dark Sword-grass Agrotis ipsilon	16	21st June	9th November

Even though it is resident in Bucks (mainly in the Chilterns) I’ve included Pyrausta despicata amongst the migrants because there seemed to be quite a fall of them in unexpected places over southern England at the time my two visitors appeared.
 

Pyrausta despicata, Westcott 12th August

Convolvulus Hawk-moth, Westcott 14th August

Silver-striped Hawk-moth, Westcott 30th July

Hummingbird Hawk-moth, Westcott 28th July

There were probably migrant individuals amongst some of the common local species too, particularly Pale Mottled Willow Caradrina clavipalpis, Angle Shades Phlogophora meticulosa, White-point Mythimna albipuncta and Turnip Moth Agrotis segetum which seemed to have a much longer season than normal, but of course we’ll never know for sure.