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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A Quick Walk down Mill Lane

 

This morning I walked along Mill Lane which runs along the east side of Hedgecourt Lake. What struck me first was the height that the Water Dock had grown to compared to the last time I visited the lake. It was at least the height of me if not taller. This is not unusual though, some plants can grow to more than 2 metres. This plant can grow in very tough conditions, these ones grow on the concrete wall of the lake against the hard wind and the severe waves that sometimes form. Equally large were the leaf mines that covered almost half of each leaf. Some leaf-mined leaves were about 75 centimetres long, so the leaf mines were huge! Whose larvae are growing up inside those leaf mines?

To identify the culprit, I visited a site I use regularly: http://www.ukflymines.co.uk
I went to the Rumex (Dock) section of the site and I saw that luckily there are not that many leaf mines on Dock in Britain. From the photos on that page I think that my species is Pegomya solennis. Pegomya solennis is a species of fly, unfortunately not new for my list although very impressive. This species is not a large fly, but the key to its very big mines lies in teamwork. In each mine there are two or more larvae that at first work together making a wide corridor. They then separate and each form a large blotch which all fuse together making one large blotch from which they feed. Sometimes the blotch size is increased even further when the blotch joins the blotch from a different leaf mine.

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The larvae feed on the leaf from inside these blotches.

Along the grassy verge between the lane and the lake there are several large patches of Bird’s-foot Trefoil, Ribwort Plantain and Black Medick. I thought these large patches might hold some specialist species but alas not much was swept from them using my net. The only species of interest was a single Platycheirus peltatus, a species of hoverfly and my 94th fly species on my Pan-species List.

Moving on, it was still windy and not too warm so most of the wildlife was hiding away. I stepped down onto one of the fishing jetties to get a closer view of the lake wall without the risk of falling in to the nippy water. On top of the concrete wall was a hole, which was occupied…

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The white spherical object in the centre of the hole is an egg sac, which belongs to a very large spider. I tried to coax it out from the hole, but it wouldn’t come. I’m not certain what it is, but one possibility is the mouse spider, Scotophaeus blackwalli. However it is usually found in sheltered places indoors so I’m not sure what it is doing on this exposed wall if I am correct.

On some more Water Dock further along I noticed a colony of aphids. It is often not hard to identify aphids when you see a colony on a particular species of plant. For this one I just searched with Google ‘aphids on dock’ and I was presented with two options: Aphis rumicis and Aphis fabae. Aphis rumicis is more plant-specific, being found on mainly dock and sometimes on rhubarb. Aphis fabae (the Black Bean Aphid), is much less so being found on a wide range of vegetables. Unfortunately the two are quite similar, although I am leaning towards A. fabae due to the paler legs shown in many of the photos I have seen on this species. My 50th hemipteroid (bug) for my Pan-species List! In my (not great) photo, the colony appears to be being attended by a Lasius ant.

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Suddenly the sun emerged from behind the clouds and everything seemed to suddenly wake up. There were loads of umbellifers on the lake shore which were great for invertebrates although I had little time to examine them closely. What I did find, however, is a mini-miner. These are very tiny bees in the genus Andrena, which I don’t come across too often. Their larger relatives in the same genus I more often come across. There are 10 mini-miner species compared to 57 other Andrena species, although I find them much harder to identify. Also, many of them have very restricted distributions.

I potted this tiny bee and when I arrived back home I took a few hasty shots though the gap between the lid and the pot. The long, very white hair caught my eye and helped me when I attempted to identify it using Steven Falk’s Field Guide to the Bees of Great Britain and Ireland. Currently I think the most likely species is Andrena niveata, the Long-fringed Mini-miner. Modern records are restricted to South-east England and it is not very common, therefore I am tentative with my identification and I will hopefully get it checked under the microscope or with an expert. In the book it says: ‘the body hairs are much whiter than in other mini-miners…the overall effect is thus of a very silvery, strongly marked mini-miner’. This definitely fits my bee.

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I was very pleased with the number of interesting and new species that I found this morning, given the short amount of time and the unfavourable weather conditions. I can’t wait until the summer holidays when there will be more time to explore!