Brighton blues

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.

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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.

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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.

 

Golden Robber

Diptera, the true flies, are not one of the most glamorous groups I must admit. However, they are one of my favourites because of the sheer diversity of shapes, sizes and colours. I recently added my 100th fly species to my Pan-species List, a figure I have been working towards for quite a while now. The fly species that I am writing about today was my 103rd.

Yesterday I went on another Hedgecourt Invertebrate Survey trip to try to add more species to my list. There was lots about and only about 10 metres into the reserve I was distracted by the many invertebrates I was recording. These included a White-legged Damselfly and a snipefly (Rhagio tringarius) that voluntarily flew into my net. I was so distracted that at first I didn’t notice a medium sized black fly that had landed on my hand. Annoyingly it was on my right hand, my camera hand, so I found it difficult to take a photo. Then I realised that it was strangely placid, and I coaxed it onto my left hand where I was able to photograph it.

The fly had its wings folded back, which made it look like a Bibio. However, when I blew the wings apart and off from the abdomen it clearly wasn’t a Bibio. It had a long abdomen with a ring of golden hairs between each tergite (segment). To identify it I posted the photo on the identification forum on the Dipterists Forum website. The Dipterists Forum is a society set up for the study of flies. The Dipterists Forum run regular field meetings, such as the current one in Canterbury, curate Diptera-related Wiki pages and a whole host of online forums and run recording schemes for different fly groups. I received an identification for my fly very quickly: it was the Golden-haired Robberfly.

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Before I saw this one, I hadn’t seen a robberfly for a surprisingly long time although they are very interesting insects. They belong to the family Asilidae, with about 5000 species worldwide. The alternative name ‘assassin fly’ is very appropriate as they are very effective hunters that tackle difficult prey like wasps and occasionally even dragonflies. They are very fast flying, allowing them to outpace most of their prey. They are also patient, sitting on a sunny plant or log waiting for suitable prey to fly past. Even robberfly larvae are formidable predators, feeding on other insect larvae and eggs beneath the soil.

This robberfly wasn’t the only interesting invertebrate I found on my survey trip. I also found two caterpillars that I have been wanting to see for a long time: Mullein Moth caterpillars. They are very impressive and, as the name suggests, they usually feed on Mullein. However, some other plants are sometimes also fed on. I found mine in a habitat I really wouldn’t expect to see them in. I have never seen Mullein growing in Hedgecourt at all… let alone a wet reedbed! Still, there they were, a pair of them. They were large, well grown, and stunningly coloured.

If they weren’t feeding on Mullein, then what were they feeding on? Water Figwort has been recorded at Hedgecourt, and is apparently a known foodplant. Unfortunately at the time I didn’t note down what they were feeding on but I will look to see if there is any Water Figwort where the caterpillars were feeding the next time I visit.

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Canary-shouldered, Purple and Early, a Thorny Moth Trap!

When I checked the moth trap on the morning of August the 2nd, there weren’t as many moths as there usually is. However, there were many species I’ve never seen before, including three species of Thorns. Thorns can be identified by the way they hold their wings – not flat like most moths but angled upwards.

The first species of Thorn I found by the trap was the Purple Thorn, which was resting on the sheet. It’s a pretty large moth, the individual I caught had a wingspan of 34mm. However that’s not the species’ maximum wingspan. The Purple Thorn has two broods (generations) each year, the first flying in April and May and the second flying in July and August. The first brood has a larger wingspan, whereas the second has a smaller wingspan, and the moth we caught was from the second brood. The species is fairly common in the south, and prefers habitats like woodland and heathland. However, it gets scarcer as you move northwards. It is patchily distributed in Scotland, with the main stronghold being around the Moray Firth. It’s common in Wales, but practically absent from Ireland.

Purple Thorn

Purple Thorn, above view

Purple Thorn

Purple Thorn, side view

The second species found, the Canary-shouldered Thorn, was perched on the metal bit which holds up the bulb. It’s the prettiest species we caught, with a bright canary-yellow thorax and yellowy-orange wings. It is also the largest species, even larger than the Purple Thorn, and it also only has one generation. It’s widespread throughout the UK, from Cornwall to Orkney, although like the Purple Thorn, it’s scarcer in Scotland. However, this might be because there are fewer recorders up in the highlands, and there are many concentrated around the South-East (like me). The Canary-shouldered Thorn can also be found in Northern Ireland and even the Isle of Man.

Canary-shouldered Thorn

Canary-shouldered Thorn

The last Thorn species is called the Early Thorn. It’s by far the smallest species and, like the Purple Thorn, has two broods each year. We caught an individual from the second brood which flies from August-September. The first flies from April-May. Even though it might be the smallest, it’s the most widely distributed, being found on Scilly as well as England, Northern Ireland, Wales, Scotland (including Orkney) and the Isle of Man. It’s identifiable by the way it holds its wings, flat above the body like a butterfly. A melanic (dark) form of this species is fairly common in Northern England, but rare down here in the South.

Early Thorn

Early Thorn

The reason we put the moth trap out was because I had an event planned for the following morning. I thought that as I lived in a small, quiet village it would be nice to teach the people who live in my village a little bit about the moths found in their area. I invited all the people I knew from the village and was pleasantly surprised that quite a few people decided to come! I even got a few to sign up to my monthly natural history newsletter, which I will be writing for the residents.