Over 900 insect species discovered in woodland in the Scottish Highlands

A TENACIOUS ecologist has identified 946 species of mostly flying insects in a West Highland wood – and he is still counting.

Dogged dipterist Ian Strachan’s marathon microscope effort began with samples taken five years ago at Loch Arkaig Pine Forest in Lochaber.

Writing on The Woodland Trust website, George Anderson says that the study is thought to be the most thorough ever conducted in a western pinewood in Scotland’s rainforest zone and shows the amazing biodiversity of the habitat. It also shows the extraordinary tenacity of a man with a passion for nature.

Loch Arkaig Pine Forest was bought by Woodland Trust Scotland and local group Arkaig Community Forest in 2016. Funding raised by players of People’s Postcode Lottery has contributed to the purchase of the site and the ongoing restoration work.

Various baseline surveys were commissioned to assess what was in the wood – including birds, fungi and lichens. Strachan, from nearby Roy Bridge, was commissioned to survey the insect life.

Strachan said, “The minute you say West Highland insects most people think of the dreaded biting midge. Many will be amazed just how small a component those and other biters like clegs are in the scheme of things. There is much more buzzing around at Loch Arkaig than biting midges, though they do have a particular talent for making their presence felt.”

Strachan took his first samples from two locations in the forest in 2018 using Malaise traps – tent-like contraptions that funnel flying insects into a jar of preservative alcohol.

He then set about the laborious task of separating out and identifying individual specimens under a microscope. By the time he had sent in his first report in 2020 he had identified 316 species, including two fungus gnats entirely new to the UK. Boletina gusakovae is usually found in Finland and Russia and Mycetophila idonea in Estonia, Poland, Slovakia, Georgia and Luxembourg.

Since then Strachan has continued to work his way through the rest of his original 2018 samples. His species total from those has now reached 650. In addition, some further samples were taken in 2021 using techniques including sweep netting and water traps. This has added a further 219 species to Ian’s list.

The grand total to date is 946 invertebrate species made up of 869 flying insects including midges, dance flies, hoverflies, fungus gnats, barkflies, mayflies, stoneflies, dragonflies, alderflies and caddis flies – plus 77 non-flying species, mostly spiders but also including millipedes, centipedes, woodlice, springtails and ticks.

Strachan is still counting, and it could take years to ID every smudge and smut in his samples which contain tens of thousands of individual specimens. He reckons he may be only two thirds of the way through the mass of preserved insects.

The Malaise trap samples have been sorted to at least family level but individual insects sometimes sit in jars at the National Museum of Scotland waiting until the right expert can be found to name their species.

Specimens of fairy wasps have been sent to the Natural History Museum in London and are awaiting identification. These tiny parasites lay their eggs inside other insect eggs and are the smallest insects known to science.

For other tricky groups Ian has turned to specialists from across the country for help, including members of the Malloch Society (Scottish fly enthusiasts). In a few cases he has had to look abroad. Prof Massimo Olmi in Milan identified tiny pincer wasps from the samples.

Meanwhile word of Strachan’s marathon effort is spreading around the international scientific community. He sent specimens of biting midges to Canada where world expert Dr Art Borkent is writing an identification key.

Strachan said, “This has been a really challenging but satisfying process, investigating the remarkable insect diversity of these woodlands. My findings are attracting a lot of interest from other entomologists and ecologists. I am not aware of a more exhaustive study ever having been carried out in a western pinewood. I am grateful for the support of my son Alasdair and a host of insect enthusiasts, notably Iain MacGowan and members of the Malloch Society and the Highland Biological Recording Group.”

Laura Chow, Head of Charities at People’s Postcode Lottery, said: “This is a quite remarkable piece of work, and we applaud Ian Strachan’s extraordinary tenacity. Flies might not seem as glamorous an area to work in as say birds of prey or wildcats, but they are just as important. These findings will help us understand the amazing biodiversity of these woods and will guide restoration efforts in the coming years – we’re delighted support from our players continues to assist with this.”

Ian will be giving a talk about his findings at the annual meeting of the Dipterists’ Forum to be held in November at the National Museum of Scotland in Edinburgh.

Of the species found in the survey so far at least 50 are considered Rare or Scarce in Britain, with almost a third of them included on national Red Lists as Vulnerable or Threatened.

Some of Strachan’s most exciting finds have been dance flies (Empids). He found five females of Anthalia beatricella, one of the smallest British species at just 1.7mm long. This is the first record for Scotland. It was first described in 1992, from Windsor Forest, and is known from just three other sites in England and one in Wales. The larvae are thought to live in rotting wood – dead and decaying timber is an important habitat for many of the insects found.

He found three other rare dance flies: Tachypeza fennica, the third British record (previously recorded in Wester Ross and Sutherland), a single male of Chelifera angusta, only the second record for Scotland, with just four other GB records, from England, and a pair of Platypalpus rapidoides, the third Scottish record.

The lance fly Lonchaea deutschi was also collected in one of the traps in 2018 and is only the second record for Britain.

The loch was a filming location for a sequence in Harry Potter and the Deathly Hallows. Harry, Hermione and Ron cling to a dragon as it flies above the forest before jumping off into the Loch below. Filming on the loch shore had to be cut short because the midge onslaught was so fierce.


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