Nemoura cinerea Stonefly, Talkin Tarn, 25 June 18 (2 of 2)
Nemoura cinerea stonefly (female) found on a fencepost near Talkin Tarn, 25 June 18. (See Photo 1 for background.)
This specimen was collected in order establish its species using the Ref 1/Ref 2 keys with the aid of my SX10D microscope.
The first step in the process is to determine its family. The fact that it does not possess long cerci (insert top right), the three tarsal segments are not of roughly the same length (insert bottom left), and the forewing contains an "X-like figure" (main photo) means that it's a Nemouridae.
There are 11 UK species in this group and in order to separate them it's necessary to examine the end of the abdomen from the underside. The specimen was cleared in 10% KOH overnight and then viewed and photographed using transmitted light as shown in the insert top right.
The insect is clearly a female, and a quick study of the sketches included in the Ref 2 section for Nemouridae allows five to be immediately eliminated, leaving just five Nemoura and a single Nemurella species to consider further. Although not immediately apparent, close examination of the sub-genital plate (uppermost in the insert) reveals that the specimen can only be Nemoura cinerea, as this is the only one of the six that has three lobes. The Ref 2 text states that the plate extends to the ninth sternum, which is not as shown in the insert, as there is a clear gap between the two. However, this is presumably a result of the clearing/soaking process, as all of the plates have separated, and so this feature can be dismissed.*
As shown in Photo 1, the insect was found in close proximity to a body of still water (Talkin Tarn) with plenty of emergent vegetation, which is consistent with the habitat outlined in Ref 2. Also it's typically seen between March and July.
Although there are a number of Nemoura cinerea Cumbrian records shown on NBN Atlas, they're mainly for the southern half of the county. However, it would appear to be widespread in the bordering county of Northumberland, and so it's probably not a locally scarce species.
* Note added 28 June: the stonefly was gravid, although I don't know whether this is relevant.
Ref 1: Pryce, Macadam and Brooks "Guide to the British Stonefly (Plecoptera) families: adults and larvae", FSC, 2007
Ref 2: H B N Hynes "A Key to the Adults and Nymphs of the British Stoneflies (Plecoptera)", Freshwater Biological Association, Scientific Publication No 17, 1958.
Note added 16 July: Comments regarding county records should be ignored - see notes to photo posted 15 July 18.
Nemoura cinerea Stonefly, Talkin Tarn, 25 June 18 (2 of 2)
Nemoura cinerea stonefly (female) found on a fencepost near Talkin Tarn, 25 June 18. (See Photo 1 for background.)
This specimen was collected in order establish its species using the Ref 1/Ref 2 keys with the aid of my SX10D microscope.
The first step in the process is to determine its family. The fact that it does not possess long cerci (insert top right), the three tarsal segments are not of roughly the same length (insert bottom left), and the forewing contains an "X-like figure" (main photo) means that it's a Nemouridae.
There are 11 UK species in this group and in order to separate them it's necessary to examine the end of the abdomen from the underside. The specimen was cleared in 10% KOH overnight and then viewed and photographed using transmitted light as shown in the insert top right.
The insect is clearly a female, and a quick study of the sketches included in the Ref 2 section for Nemouridae allows five to be immediately eliminated, leaving just five Nemoura and a single Nemurella species to consider further. Although not immediately apparent, close examination of the sub-genital plate (uppermost in the insert) reveals that the specimen can only be Nemoura cinerea, as this is the only one of the six that has three lobes. The Ref 2 text states that the plate extends to the ninth sternum, which is not as shown in the insert, as there is a clear gap between the two. However, this is presumably a result of the clearing/soaking process, as all of the plates have separated, and so this feature can be dismissed.*
As shown in Photo 1, the insect was found in close proximity to a body of still water (Talkin Tarn) with plenty of emergent vegetation, which is consistent with the habitat outlined in Ref 2. Also it's typically seen between March and July.
Although there are a number of Nemoura cinerea Cumbrian records shown on NBN Atlas, they're mainly for the southern half of the county. However, it would appear to be widespread in the bordering county of Northumberland, and so it's probably not a locally scarce species.
* Note added 28 June: the stonefly was gravid, although I don't know whether this is relevant.
Ref 1: Pryce, Macadam and Brooks "Guide to the British Stonefly (Plecoptera) families: adults and larvae", FSC, 2007
Ref 2: H B N Hynes "A Key to the Adults and Nymphs of the British Stoneflies (Plecoptera)", Freshwater Biological Association, Scientific Publication No 17, 1958.
Note added 16 July: Comments regarding county records should be ignored - see notes to photo posted 15 July 18.