Michael Raupach et all have described Plea cryptica as a new species for Europe and have differentiated it from Plea minutissima. It appears to be found in the same habitat and can only be differentiated in males. The key features being:
Plea minutissima (male)
Viewing dorsally has a dark scutellum and pronotum (Colour is variable)
A distinct dark brown bar between the eyes (Colour can be variable)
Male left paramere shorter and wider, more hooked with a rounded tip
Plea cryptica (male)
Viewing dorsally has a light brown scutellum and pronotum (Colour is variable)
A diffuse light brown bar between the eyes (Colour can be variable)
Male left paramere slightly more longer than wider and elongated
Out of the 3 UK samples they analysed they did not find it but did find it in Belgium .
I have now managed to dissect some samples myself and have found 3 males all of which the left paramere matched Plea minutissima. The colouration of the pronotum, scutellum and bar between the eyes was quite variable in colouration with the pronotum and scutellum having pale patches. They do seem a little darker than the females which did look more like the colouration of Plea cryptica and that can be confusing before you confirm them as male/female. It would be good to have a sample of both and see them side by side and I expect that in males one will be slightly darker than the other.
My assessment for now is that i cannot trust just the colouration features and on iRecord will assume they are Plea minutissima unless the genitalia proves otherwise.
However i will be checking every one from now and I am sure it won’t be long before it is found in the UK – Good searching!
The reference for the paper is:
Michael Raupach, Nele Charzinski, Adrian Villastrigo, Martin Gossner, Ralf Niedringhaus, Peter Schafer, Sebastian Schmelzle, Gerhard Straub & Lars Hendrich. (2024). The discovery of an overseen pygmy backswimmer in Europe (Heteroptera, Nepomorpha, Pleidae). Sci Rep 14, 28139
Aquatic Bugs 