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  • Writer's pictureSim Elliott

Mating Long-Tailed Blue Butterflies. Brighton. 25.08.22

I am not going to reveal the exact location in Brighton of this sighting; but if you are a butterfly enthusiast you'll know where this site is. It is a ten minute walk from my house!

I had visited this site many times in the last few weeks, looking for Long-Tailed Blues and not see any; then this afternoon I struck lucky!

I saw them with a lovely fellow Butterfly enthusiast who had travelled a long way to see them. I had this site visited many times, and not seen any on previous trips. We initially saw a couple of fly-pasts, then two butterflies, that I initially thought were Common Blues, were circling each other. They settled on grass (I think a South Downs fescue grass), opposite a clump of everlasting sweet pea and started mating, and moved to another plant (that looked like an Aster, but not in flower) briefly before returning to the grass. I watched them for 30 minutes mating, and they were still mating when I left. I don't know if the female will lay her eggs on the everlasting sweet pea or return to where they migrated from to lay. It is possible they themselves emerged from Brighton-laid eggs as caterpillars.

I have reported this sighting and sent photos to the County Recorder for Sussex.

All sections of text in italics are quotations; sources cited at the end of each quotation

The Long-tailed Blue is an extremely rare migrant to the British Isles. It was first recorded from Brighton in East Sussex, and Christchurch in Hampshire, in August 1859. By 1939 a mere 36 sightings had been recorded - mostly of individuals. Between 1940 and 1988 another 85 sightings were recorded. The only major immigration was in 1945, a good year for migrants in general, when there were 38 sightings. A recent immigrant was observed in Hampshire in 2006.

However, the most noticeable influx occurred in 2013 when Long-tailed Blue were seen at 9 sites in Devon, Hampshire, Sussex, Kent and Suffolk. Mating pairs, eggs and larvae were also found, confirming that the species had successfully bred and, on 8th September 2013, the first of the offspring emerged in Wiltshire and Kent. Sightings from other counties followed, with sightings continuing into October.

On the continent, this butterfly is considered a pest of pea crops, one of the larval foodplants, where it can cause considerable damage. This butterfly is continuously-brooded on the continent but is unable to survive our winters. Although this species is a rare migrant to the British Isles, it is one of the most-widely distributed Lycaenids in the world. The vast majority of records in the British Isles are from the south of England and the Channel Islands. UK Butterflies - Long-tailed Blue - Lampides boeticus

The Long-tailed Blue is an exotic migrant from the Mediterranean with a handful typically reaching UK shores each year, but experts believe climate change is behind this butterfly reaching our shores more regularly and in vastly increased numbers.

One of the largest migrations took place in 2015 when 60 adult butterflies crossed the Channel in August and laid 1000s of eggs in gardens and allotments along the South Coast.

The butterfly gets its name from the wispy ‘tails’ on the trailing edge of each of its hindwings, which flutter in the breeze. Adjacent eye spots fool birds into thinking this is the head of the butterfly, allowing it to escape any attacks unharmed.

The male is a striking violet-blue colour, while the female is a mix of duller blue and brown. The underside of both sexes is a sandy brown colour crossed by numerous white, wavy lines.

Size and Family

  • Family: Blues

  • Size: Small

  • Wing Span Range (male to female): 32-42mm

Conservation Status

  • Butterfly Conservation priority: Low

  • European status: Stable

Caterpillar Foodplants

Caterpillars feed primarily on plants in the legume family, including Bladder-senna (Colutea arborescens), Broad-leaved Everlasting-pea (Lathyrus latifolius), Broom (Cytisus scoparius) and Narrow-leaved Everlasting-pea (Lathyrus sylvestris). Mange-tout pea (Pisum sativum) is also used.


The adult butterfly is most-often seen flying around garden flowers, especially those which are potential foodplants. However, it may also be found on open downland.


In recent years the Long-tailed Blue has provided the Sussex butterfly enthusiast with some of the most exciting times in the entire history of the county's Lepidoptera, most notably the annus mirabilis of 2013. This account also draws on the second of two unprecedented influxes of this previously very rare immigrant, during the post atlas survey year of 2015. The opportunity to include such significant data could not be overlooked.

This is one of the world's more widespread and successful species, being distributed across Africa, southern Asia and Australia. In Europe it is only permanently resident along the Mediterranean belt. It is a highly adapted and enthusiastic traveller, with a well documented ability to cross seas and mountain ranges. The Long-tailed Blue is capable of both high speed and endurance.

Each summer it migrates northwards into more temperate parts of Europe, but historically has only rarely penetrated as far north as the South of England, at least in any numbers. Previously, only 1945 and 1990 have seen incursions of any significance, but the summer of 2013 was to break that mould, and the re-run in 2015 seems to suggest that a new era has been ushered in.

The general consensus remains that it is as yet unproven whether these movements are of a truly migratory nature, involving annual population shift and counter-shift, or sporadic, irruptive, one-way adventures. However, I consider that the circumstantial evidence for the former is becoming ever stronger.

Furthermore, I believe that the influx of such large numbers in 2018, so soon after the 2013 event, does suggest hat the species is undergoing significant change in either its geographical range or its behaviour, with the former being wore likely I suspect that the butterfly's southern bot of permanent residency in Europe is shitting northwards in response to climate change, and that annual forays are therefore reaching further worth into mainland Europe and, happily, into Sussex and the wider South of England, both more regularly and in greater numbers.

Only the passage of time will determine whether this theory holds water, but while so many of our resident butterflies are facing serious problems, w some of which are likely to be exacerbated by Climate change, it is exciting to speculate that species such as the Long-tailed Blue may be more likely to grace our shores in the future.

The formerly once-in-a-lifetime encounter with a Long-tailed Blue will never disappoint. as the butterfly seems to bring with it a taste of the Mediterranean and, for many, memories of gest holiday encounters. It has a characteristic, rapid, hairstreak-like flight pattern, making it difficult to follow, particularly when the highly pugnacious makes launch themselves headlong into combat. Whereas other species are pursued at low level rival Long-tails zip rapidly skywards in jousts, rather like the Duke of Burgundy . Michael Blencowe and Neil Hulme (2017) The Butterflies of Sussex: A Twenty-First Century Atlas



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