Plecoptera of the British Isles

Plecoptera of the British Isles

Plecoptera of the British Isles - UK and Ireland : A second foolhardy venture, to accompany my caddis project. . i) To monitor adult stonefly observati

A second foolhardy venture, to accompany my caddis project.
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i) To monitor adult stonefly observations and identifications in Britain and Ireland.
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ii) To review existing observations and identifications.
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There are 34 or 35 stonefly species on the British Isles list, depending upon how one counts them - i.e. including or excluding the probably extinct Isoperla obscura, the only ever doubtfully British Xanthoperla apicalis, and/or the recent arrival/discovery Nemoura lacustris.
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Only about nine or 10 of these species are reliably identifiable in the field / from photographs (although phenology can help in some instances), so my main objective is to try to bring observations to family and, in some cases, genus level - species level is very much the exception.
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There are four species in the Taeniopterygidae family, and all are probably positively identifiable from high quality photographs capturing key features (not that stoneflies, which are highly sensitive to vibrations, necessarily lend themselves to high quality photographs in the field). One species - Brachyptera putata - is the subject of a Biodiversity Action Plan and receives attention as a British endemic with a core range in the Scottish Highlands. It is usually reliably distinguishable in photographs from the closely-related Brachyptera risi, although some B risi have been mistaken for B putata, and it is important to note that risi also appears across large areas of Scotland, so a Highland Brachyptera stonefly is not necessarily B putata..
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Most if not all of the observations of the Nemouridae remain at family level.
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The family Leuctridae contains only the genus Leuctra in the British Isles (at least if the binominal Leuctra geniculata is preferred and Euleuctra geniculata deprecated), so genus-level identification is standard on iSpot. However, Leuctra geniculata is easily identified from a high quality photograph showing the antennae and, by default, an autumnal (Sept-Oct-Nov) Leuctra lacking geniculata's diagnostic features is very likely Leuctra fusca by default.
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Currently, there appear to be no observations of the Capniidae family on iSpot.
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The delicate, yellow Chloroperlidae are readily identifiable at family level but do not seem to be frequently reported.
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The Perlidae and Perlodidae families, which contain medium to large and sometimes quite striking stoneflies, including brachypterous males, are frequently reported on iSpot, presumably because of the attention they will attract (compared, for example, to a diminutive Leuctra species). One species - Isogenus nubecula - is very rare, if it still survives as a British species on the River Dee in Flintshire, and the subject of a Biodiversity Action Plan. Unsurprisingly, there are no records on iSpot. A second species - Perlodes mortoni, recently split from the now continental European Perlodes microcephalus - is the subject of a recording scheme by the Riverfly Partnership and this, as well as its quite striking appearance and orange stripe down the centre of the head and pronotum, mean that it is frequently reported. However, it is important to note that other species have or may have the same pattern, if not the same orange colouration of P mortoni - these are Diura bicaudata and Isogenus nubecula (although, as just mentioned, one is not likely to encounter the latter species).
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Resources used:
a) Guide to the British Plecoptera (Stonefly) Families: Adults and Larvae, by Pryce, Macadam & Brooks, pub Field Studies Council, 2007
b) A Key to the Adults & Nymphs of the British Stoneflies (Plecoptera), by Hynes, pub Freshwater Biological Association, 1977
c) Handbook vol I, part 6: Plecoptera, by Kimmins, pub Royal Entomological Society, 1950
02 Oct 2019
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