With our changing climate, distributions and abundances of a wide range of invertebrates are ever-changing. In this regard, the headline butterfly event of the year was the record-breaking influx of long-tailed blues, reaching the British coast from their regular haunts of southern Europe. At the moment, in September, the offspring of the first wave of primary migrants are emerging from the broad-leaved everlasting-pea plants on which the females had laid their eggs in late August, allowing keen lepidopterists another chance to see this elusive species. However, I did not need this second chance – I was fortunate enough to lay eyes on some of this year’s earliest arrivals.
Walking up Whitehawk Hill on the late summer day of 29th August felt typical, 20 degrees yet with a fresh breeze blowing up from the Channel. However, what I was about to witness was an indication of our warming planet.
Upon reaching the top of the hill, I immediately saw two small butterflies spiralling frantically upwards against the expanse of Brighton in the background. I knew exactly what they were – territorial male long-tailed blues. These were small, dainty yet tireless butterflies, which had crossed the Channel and much of Western Europe to gambol between the community allotments and the scrubby border of the local nature reserve in the shade of the transmission tower.
During brief interludes between the combat, these two males and a further individual occasionally paused on ground vegetation, allowing photo opportunities and examination of the species’ beautiful intricacies. The long-tailed blue is so-called on account of the two ‘tails’ which project backwards from the hindwing. These mimic the antennae of the butterfly, and coupled with the eye-spots on both the upper and lower surfaces, the tactic is to make predators attack this end of the insect, thinking it is the head. This protects the actual head from any damage from hungry insectivores.
The photo below shows one of the more worn-looking blues. There are chunks missing from the left hindwing where the eye-spot usually is, suggesting a predator mistakenly attacked the rear end of the butterfly, fooled by the fake antennae. This left only superficial damage to the butterfly.
I did not expect finding these long-tailed blues to be quite so easy, and in the past it certainly wouldn’t have been. The first British record of this species was from Brighton all the way back in 1859 (leading to one of its earlier vernacular names being the Brighton argus), although in the succeeding 80 years it had only been sighted again 36 times. The number of sightings more than doubled between 1940 and 1988, with a large proportion of these being during an influx in 1945. However, it took until 2013 and 2015 before the long-tailed blue numbers really became significant, when relatively major immigrations took place into the southern counties. Already it is looking likely that the 2019 influx will surpass all previous influxes.
But why are these long-tailed blues making an effort to reach our shores? There are many other butterfly species which have similar distributions to the long-tailed blue in southern Europe, although they have made no attempt to colonise the UK. However, the long-tailed blue is not only found around the Mediterranean – one of the world’s most successful butterfly species, its distribution also stretches right down to Australia. For such a small lepidopteran, its flight is powerful and determined, showing no reluctance to cross seas and mountain ranges such as the Channel and the Pyrenees. Furthermore, the long-tailed blue is renowned for its ability to pass through its entire life-cycle incredibly quickly. Despite most primary migrants only appearing in the UK in late August, their offspring already started to emerge as adults in mid-September. This allows the long-tailed blue to gain a foothold on new lands with great speed, which gives this species a huge advantage in the face of increasing temperatures in the long-tailed blue’s ancestral homelands. Although the current year-round climate of the UK is too cold for the species to overwinter, it is quite possible that it won’t be long before it is resident in the UK and there will be more chances to admire this resolute butterfly.