COLLEMBOLA > ENTOMOBRYOMORPHA > ENTOMOBRYOIDEA > Isotomidae > Anurophorinae

Isotomidae includes two primary subfamilies, Anurophorinae and Isotominae.

I believe that the individuals shown in the following photos are from the Anurophorinae subfamily, initially considering species in the genera Folsomia, Hemisotoma (Cryptopygus) and Proisotoma.

Although the important distinguishing features can only be determined with microscopic examination, it should be possible to confirm the genus from photos by looking closely at the abdominal segments. In Folsomia the final segments abd4+5+6 are always fused together, whereas abd4 appears to be distinct in the specimens seen here, so Folsomia can be disregarded. Separation of abd4 is difficult to see, but it's reasonably clear that abd5+6 are fused, and that rules out Proisotoma as in that genus they are separate.

Hemisotoma thermophila, also widely recorded as Cryptopygus thermophilus, is a variably coloured, pale brownish-grey species, about 1.5mm long, with eyes usually consisting of eight, although occasionally six or seven, ocelli in an elongated pattern. The species lacks anal spines, but does have several long setae on the dorsal side of the posterior abdominal segment that bear a fringe of miniscule 'hairs' about halfway along their length. They are generally referred to as 'foil setae' and, if visible, which in virtually all cases they're not, would provide confirmation of the species.

Otherwise, we're reliant here with trying to visually distinguish the species based on the general body form, particularly in respect of the fusing or not of the abdominal segments, size, colour and the appearance of the eye-patch.

A final point to note, is that the British checklist and 'key' confirm that the species grows to a maximum of 1mm long, whilst in Europe the size is given as 1.8mm. It doesn't sound much, but it's pushing towards nearly twice the length, which is pretty significant. I only mention this as the individuals featured here were certainly a tad longer than 1mm.

I can't find any specific information in respect of preferred habitat, nor much regarding their current distribution. The NBN Atlas only has forty-four records nationwide and only one of those appears to have been accepted. The unconfirmed sightings are all from around London and the home counties, Wales or Ireland. That said, the species was regarded as being moderately common across central and southern counties when the 'key' was first published in 2007.