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There are several records for 'Entomobrya muscorum' in the literature. However, South (1961) said 'Entomobrya muscorum has been recorded in the literature from 14 counties in the British Isles but, since it has frequently been confused with Degeeria muscorum Tullberg 1871 [=Entomobrya nicoleti], the records are probably suspect'.
In Gisin (1960) and Stach (1963), the main character used to key out Entomobrya muscorum Nicolet is the very small length of the third abdominal segment (abd3) on the dorsal midline in comparison to abd4. Gisin (1960) [my translation] keys out Entomobrya muscorum as having 'Abd.IV 5-15 times as long as Abd.III' whereas the other Entomobrya which concern us have 'Abd.IV 2-5 times as long as Abd.III'. [The length of the antennae relative to the body is also used but I have found this character to be too variable to be reliable]. None of the Entomobrya I have examined in the NHML collection have abd4 more than four times as long as abd3, including the holotype of Entomobrya macrocerata Bagnall 1917 (Fig. 1) which is supposed to be junior synonym of Entomobrya muscorum (but which I believe to be a junior synonym of Entomobrya nivalis).
It seems to me that records for 'Entomobrya muscorum' from Britain and Ireland refer to other Entomobrya species. Perhaps some of them are particularly large (>2.5 mm) specimens of Entomobrya nivalis which have antennae more than half as long as the body?
I suspect that the 'Entomobrya intermedia' of Brook (1884) which South (1961) found in '13 counties in England and Wales' is also a probable junior synonym of Entomobrya nivalis. South (1961) did not use the length of the abdominal segments in his key and relied almost entirely on dorsal pigmentation which is variable.
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