The weather in the second half of September started fairy unexceptionally, but high pressure began to build in the fourth week, and by the start of October England saw record-equalling temperatures of 29°C in many places. Light winds with origins from as far as the mid-Atlantic, North Africa and the Mediterranean funnelled in to produce a classic recipe for a long-awaited late-summer influx of continental moths. It was warm for several days before any obvious arrival, giving ample opportunity for keen moth-ers to take up positions on the south coast.
It was surprising that arguably the best moth of the period came in the vanguard, nine days before the real army of immigrants. Roy Eden's lifetime ambition was fulfilled on the morning of 21st September, when he found a gorgeous Oleander Hawkmoth sitting on top of his garden actinic trap at his home at West Bexington (Dorset). Roy commented that although he had, during his long spell on the Dorset coast, caught three Death's Head Hawkmoths and over 100 Convolvulus Hawkmoths, this was the pinnacle of his moth-ing career.
Oleander Hawkmoth (Dorset) (Paul Harris).
Roy Eden's 'subtropical garden' in West Bexington (Dorset) (Steve Whitehouse).
A few days later on St. Mary's (Scilly), Mick Scott's Scar Bank Gem caught overnight on the 23rd was more evidence that some exciting times were just round the corner.
Scar Bank Germ, St. Mary's (Scilly) (Mick Scott).
Back on the Dorset coast, visiting moth-trappers at Durston Country Park had some moderate success over the next few nights with several Convolvulus Hawkmoths, two Pale-Lemon Sallows, and three Small Marbleds amongst some commoner migrants, and good numbers of the now resident Sombre Brocade. Reports of migrants were now starting to come in from many places around southern Britain as temperatures soared into the high 20s.
Pale-lemon Sallow, Durlston Country Park (Dorset) (Matthew Deans).
It soon became very evident that the far southwest of England was going to feature big-time, as news of a Dark Mottled Willow at Sennen Cove (Cornwall) and nearby a Slender Burnished Brass at Nanquidno on the 28th hit the airwaves. Neither of these species are annual and to have both recorded at sites barely two miles apart set pulses racing for the forthcoming weekend.
Dark Mottled Willow, Sennen Cove (Cornwall) (Steve Whitehouse).
Slender Burnished Brass, Nanquidno (Cornwall) (Chris Griffin).
It was not just southern macro moths making landfall, as several 'tropical pyralid' species in the form of Diasemiopsis ramburialis, Spoladea recurvalis and Old World Webworm began to appear in Cornwall and on the Isles of Scilly. For several nights between 29th September and 5th October comparatively large numbers of Vestal, Gem, Delicate and Scarce Bordered Straw were recorded between the Thames Estuary and the Irish Sea with numbers of Convolvulus Hawkmoth, Pearly Underwing, Small Mottled Willow and Small Marbled not far behind. A Many-lined was at West Bexington (Dorset) on the 29th, a Tunbridge Wells Gem was at Tramore (Waterford) on the 30th, while a late Rannoch Looper even got in the act on Dartmoor (Devon) also on the 30th.
Many-lined, West Bexington (Dorset), September 2011 (Dave Foot).
The Isles of Scilly moth-ers network, mainly based on St. Agnes and St. Mary's, had terrific results from the start of October with excellent numbers of nocturnal migrants as well as the first of several Purple Marbled and daytime-found Crimson Speckled. Although Mike Hicks was not initially too worried about a small, pale noctuid caught on St. Agnes on the 2nd, and even thought it might just be a Small Wainscot, his curiosity lead him to take a quick in-situ record shot and secure the insect just in case. Following rapid communications with Anglian Lepidopterist Supplies boss Jon Clifton, the moth was soon identified as a Mediterranean Corn-borer, Sesamia nonagriodes, a true first for Britain. Just as this island archipelago has enjoyed a resurgence of quality rare birds this autumn, the moths have also helped to put it back on the mega-map.
Purple Marbled (Steve Whitehouse)
Visiting moth-ers at West Bexington (Dorset) on 1st October did not quite manage to equal the results of those on Scilly, but they did manage to attract at least 20 species of migrant moth including two Cosmopolitan and a fine Dewicks' Plusia on what was a an extraordinary visual mothing night; by late evening, observers on the seafront could actually see moths arriving straight in off the sea!
Cosmopolitan, West Bexington (Dorset), October 2011 (Dave Foot).
A good visual candidate for an Eastern Nycteoline was at Dungeness Bird Observatory (Kent) on 30th September. This individual was a female and as such may be difficult to prove, as its critical parts are extremely similar to those of Oak Nycteoline, a common British species.
Nycteoline sp., Dungeness (Kent), October 2011 (Bill Urwin).
By 3rd October numbers of migrant moths had reached northwest Wales and the Isle of Man, and two days later one or two made it to southwest Scotland. A Channel Islands Moth Night in early October produced a Dumeril's Rustic, only the third islands record and a very scarce species on the British mainland in recent times.
Dumeril's Rustic, Guernsey (Channel Islands), October 2011 (Tim Peet).
As October progressed more Crimson Speckled were found, often on flowers during the daytime, with some 34 individuals reaching localities as far apart as Bardsey Island (Gwynedd), Dunwich (Suffolk) and well inland at Woodford Green (London). The latter moth arrived overnight on 4th October at a garden trap operated by Ken Murray, who was inspired to put it out having read the many reports of rare moths on Bird News Extra!
Crimson Speckled, Woodford Green (London) (Kenneth Murray).
A Golden Twin-spot was a welcome find at Portland (Dorset) on 3rd and was soon followed by two more on the Isles of Scilly. Portland scored again on the 8th with the island's second, and Britain's seventh, Egyptian Bollworm. A Porter's Rustic was on St. Mary's (Scilly) on the 8th.
Golden Twin-spot, Portland (Dorset), October 2011 (Steve Whitehouse).
At least five Death's Head Hawkmoths included one settled on drying washing on a clothes line in a Stoke-on-Trent (Staffs) garden on the 1st followed by one on the 10th at Elgin (Morayshire), a county first. A total of 14 migrant Dewick's Plusia were recorded over the period. Several of this species have also been recorded inland in Surrey this summer, and one photographed by day at Beddington recently has prompted locals to think it may have actually have bred there this year.
Dewick's Plusia (Dorset), September 2011 (Paul Harris).
As noted widely in the national press and on television, the stunning Flame Brocade appears to have colonised a few places along the south coast of England including a thriving colony discovered during this period in East Sussex. At least 25 other migrants or wandering individuals have been recorded as far west as the Isles of Scilly. Perhaps even more attractive, the Clifden Nonpareil has also done very well in the last month, expanding in its core breeding areas in Dorset, Hampshire and Sussex and other wanderers reaching Somerset and Wiltshire to the northwest.
Clifden Nonpareil (Dorset), September 2011 (Roger Wasley).
Blair's Mocha is probably breeding on the Hampshire coast, as numbers were being recorded at a suitable site well before the migrant influx. At least 13 others have been seen elsewhere since and included two inland in Buckinghamshire in early October. Clancy's Rustic does not appear to have suffered unduly as a result of two cold British winters as it continues its slow spread north, this year reaching Somerset and Surrey.
Migrant pyralid moths have been well represented in this influx and include at least five Euchromius ocellea, 56 Old World Webworm, 10 Uresiphita gilvata, 14 Antigastra catalaunalis, 20 Diasemiopsis ramburialis, 40 Spoladea recurvalis and 78 Palpita vitrealis. Five Etiella zinckenella included a county first in Yorkshire on October 2nd.
Palpita vitrealis, Tynemouth (Northumberland), September 2011 (Tom Tams).
Spoladea recurvalis Cornwall, October 2011 (Steve Whitehouse).
The following minimum numbers of scarce migrants included three Portland Ribbon Wave, 1,000 Vestal, 63 Gem, 96 Convolvulus Hawkmoth, 87 Hummingbird Hawkmoth, 11 Four-spotted Footman, 78 Pearly Underwing, 148 Delicate, 46 White-speck, 16 Cosmopolitan, 15 Pale-lemon Sallow, 46 Small Mottled Willow, six Dark Mottled Willow, 162 Scarce Bordered Straw, 12 Bordered Straw, 19 Purple Marbled, 100 Small Marbled and eight Ni Moth. Dark Sword-grass, Silver Y and Rusty-dot Pearl were very widespread.
There's also some great 'romantic' news for one of Britain's rarest breeding noctuids: a colony of Blair's Wainscot has been rediscovered on the same marsh on the Isle of Wight where Blair first discovered it, but where it was believed to have become extinct in 1952. A Shoulder-striped Wainscot in Worcestershire on 2nd October and a Hebrew Character in Yorkshire on 13th are ridiculously early emergences, no doubt brought about by the long, warm, early spring. Pupae of both had presumably developed much faster than normal and the record autumn temperatures had fooled these into thinking it was next year's summer already!
Compared to this huge immigration of moths, it has again been rather disappointing for migrant butterflies. A single Monarch was photographed beside the coastal path at Ringstead (Dorset) on 28th September and on the same day in the same county a Long-tailed Blue was at Weston, Portland. Another Long-tailed Blue was at Lowestoft (Suffolk) on 11th October followed by other singles on St. Agnes and St. Mary's (Scilly) on 12th and 13th. Numbers of Clouded Yellows increased in southern England in late September with a maximum count of 20 on The Lizard (Cornwall). A few Painted Ladies were seen. There were large numbers of Red Admirals reported across the country with 100 an hour counted migrating across Portsmouth Harbour (Hants) on 28th September.
It has been suggested that the warm front that initiated this moth movement originated in the northern Sahara and made progress up the west side of Biscay into the Western Approaches a few days later. Perhaps it is not that surprising that four Vagrant Emperor dragonflies arrived during the same period. The first was in a moth trap at Clone (Wexford) on the 1st with another the next night attracted to a moth trap in Cornwall. One was also discovered inside a house north of Annan (Dumfries & Galloway) on the 2nd and finally one was seen by day on St. Mary's (Scilly) on the 15th. A Southern Oak Bush Cricket was at Portland Bill (Dorset) on 5th October.
And so it turned out to be the best moth immigration since at least 2006. With the warm weather finally slipping away after 15th October, it is expected that migrants will fall off quite rapidly. A few individuals may continue to wander into new areas for several days to come and who knows what may happen if we get a late mild spell in late October or early November.
Waring, Townsend and Lewington. Field Guide to the Moths of Great Britain and Ireland. Revised edition, British Wildlife Publishing, 2009.
UKMoths online photographic guide