During the summer, insect traps were set on wych elms at a number of sites in Assynt. The traps (photo 1) were constructed by Lochinver Primary School and installed to detect, if present, the bark beetles Scolytus scolytus that carry Dutch Elm Disease.
This was a contribution to the Elm Action Map (TEAM), a collaborative project with local community groups such as the Field Club, NGOs and Forest Research, coordinated by the School of Geography and Sustainable Development at St Andrews University. As part of this project a Story Map is being developed, which will describe some of the iconic wych elms in the parish and raise awareness of the hazards of the Disease.
One of the sites was the old elms on the Higgledy-Piggledy Path in Culag Woods (NC090218). A trap, containing propylene glycol to preserve any catch, was installed by Romany Garnett and Andy Summers on 7th July (photo 2),
Andy emptied the trap on 15th July and again on 17th September and passed the contents over to me for identification. This proved quite challenging, since there were a variety of invertebrates in each sample.
First sample
The first sample contained one specimen of a small (7mm) but chunky plant-feeding weevil Otiorhynchus singularis, which occurs throughout the British Isles on a wide variety of broad-leaved and coniferous trees and shrubs. As in some close relatives, including the notorious pest vine weevil O. sulcatus, all individuals are female, so they reproduce by parthenogenesis (‘virgin birth’).
Most of the insects in the trap were immature common flower bugs Anthocoris nemorum with, thankfully, just one adult (4mm), which allowed me to name them. They are, again, found throughout the British Isles on a variety of trees and other vegetation, where they prey on red spider mites and aphids. So, some of the good guys!
However, the catch was dominated, size-wise, by a large (15mm), if somewhat bedraggled, cranefly (photo 3). It was a female, which makes naming rather more difficult, and I sent it off to Murdo Macdonald, who was able to identify it as Tipula variicornis. Although widely distributed across the British Isles, the only previous record from Assynt was of one caught on Loch Assynt (NC2325) by Colonel J.W. Yerbury on 2nd June 1911. Colonel Yerbury is the only dipterist known to have collected in Assynt in the first half of the 20th century.
Second sample
The second sample contained a wider variety of invertebrates. There were ten specimens, five of them adult, of the very common harvestman Mitopus morio, which occurs in a range of habitats across the Highland landscape.
There was also one spider, one of the larger ‘money spiders’ (Linyphiidae), a male Drapetisca socialis, which is an arboreal species. There is only one other local record, from the Malaise Trap operated on Little Assynt during 2010.
Flies were represented by two large and many small specimens, the latter looking suspiciously like midges. There were, again, many examples of the common flower bug Anthocoris nemorum, with a higher proportion of adults later in the year.
However, it was the beetles that were of particular interest. The largest, at nearly 30mm, was a male ground beetle Carabus problematicus, the commonest of these fearsome (for their size) blue-black predators found locally. There was a further example of the same small weevil as earlier in the year, Otiorhynchus singularis.
Finally, there was a single bark beetle, just 3mm in length and, happily, not one of the bark beetles (photo 4). I have been collecting and identifying beetles for over fifty years and have never seen the like. Its elytra are metallic dark green and most of the rest of the body, including a curious extended and flattened rostrum, orange. It belongs to a small family, the Salpingidae, that feed, as larvae, under bark, on wood-rotting fungi, but do not spread them, and it keyed out to Salpingus ruficollis. There are no records for this species mapped on NBN from the Scottish mainland north of Shieldaig (NG8572), so a nice find.
Conclusions
The wych elms at Glencanisp Lodge and elsewhere have received, for the moment, a clean bill of health, so it was unlikely that the trap would capture any scolytids. It was worth checking, nevertheless, and the exercise has added to our knowledge of the insect life of local elms and provided a couple of really interesting records. The contents of other traps will be identified, where possible, when received. Thanks to all those involved.
Ian M. Evans