Wednesday, 4 July 2018

Square-bashing in Scotland - hoverfly records

Having already reported on the fungus gnat results of my trip, I really ought to provide some information on the hoverflies.

The trip was exceptionally poor for hoverflies, with numbers extremely low at the majority of stops. I suspect that part of the reason lay in the availability of nectar sources. Apart from the buttercup verges of the more southerly areas of the west coast, the main nectar source was pignut Conopodium majus, and even this was limited. Rowan Sorbus aucuparia was almost entirely over; markedly reducing the effectiveness of my activities. So, a large part of my haul arose from sweeping.

These factors meant that the catch was dominated by smaller species, especially within the Bacchini and Chrysogastrini, with Platycheirus, Melanostoma and Sphegina making up a lot of the sample (Figure 1). The Syrphini were noteworthy by their absence, as was the genus Eristalis, although I did see E. rupium on several occasions. In total I recorded 89 species (Figure 2), which I think was substantially below what might have been possible. Amazingly, Dasysyrphus were completely absent and Syrphus were rare.
Figure 1. Numbers of records within each Tribe of hoverfly

The numbers of records look to be high, but it needs to be borne in mind that I record males and females separately, so the actual number of species-level records will be  a fair bit lower (perhaps 25%).

The high point for me was finding Platycheirus amplus, a species I've never previously found. In addition, I think I can say a bit more about the preferred habitat of Lejogaster tarsata, which seems to favour yellow flag iris Iris pseudacorus flushes close to the sea shore; especially where silverweed Potentilla anserina is flowering. The biggest surprise was Brachypalpoides lentus at a patch of Cotoneaster horizontalis at the edge of an old oak woodland. There is plenty of this habitat in the Oban/Loch Lonond area so I suspect this and other Saproxylics are probably more widely distributed than the records suggest. I have one specimen of Sphaerophoria that needs further investigation, as it does not readily fall out in the key in Stubbs & Falk; it might be interesting, but then I might be mistaken and it will prove to be something relatively common.

Figure 2. Hoverflies recorded from the north and west coasts of Scotland between 26 May and 17 June 2018

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