COLLEMBOLA > ENTOMOBRYOMORPHA > ENTOMOBRYOIDEA > Isotomidae > Isotominae

Isotomidae includes three subfamilies consisting 67 elongate-bodied species in 23 genera.

The Isotomurus genus includes nine species, one of which is probably now extinct in Britain and another which is very scarce. All the remaining species are regarded as being common to some degree or 'probably common', but under-recorded. The previous comments regarding identification and verified recording of Isotoma viridis effectively applies to all Collembola which, as far as I can see, has a direct impact on the reliable data available and, consequently, where species are being recorded. As an example, the NBN Atlas only had 623 records for all Isotomurus species at the time of writing with virtually half coming from Shropshire and only two from Dorset!

Isotomurus palustris is the most frequently recorded, but is known to be consistently confused with Isotomurus unifasciatus, which has resulted in that species being assigned the rather unsatisfactory status of 'probably common'. The situation is much the same with Isotomurus pseudopalustis, which was once part of a 'palustris group'. Isotomurus gramineus is another possible confusion species as it's bright green, leading to potential misidentification with Isotoma viridis. Of the remaining species, Isotomurus fucicolus is considered as being 'moderately common' whatever that means, and Isotomurus plumosus common on wet vegetation around pond margins.

The featured species here is Isotomurus maculatus, which was formally regarded as a variation of Isotomurus palustris, but is now recognised as a separate species. It’s around 2.5mm long, greyish green or brown in colour with scattered patches of dark pigment. Good specimens have a distinctive pattern on their body where there is at least some pigment concentrated in a mid-dorsal stripe, but with an unpigmented field on the abdominal tergites prior to the characteristic ‘backward-facing crown-shaped’ patch.

In addition to the various species accounts on the UoR website, the NatureSpot species page and associated 'Isotomurus identification guide' all provide excellent reference information to assist with correctly identifying these species.