COLLEMBOLA > SYMPHYPLEONA > Katiannidae

When you take a look at all of the available distribution and occurrence data for Sminthurinus genus species, apart from one very rare form, only three have been officially recorded in Britain in recent years; Sminthurinus aureus and Sminthurinus elegans as previously described, and Sminthurinus niger.

Further species have been described, but they are mainly listed as 'status unclear'. One such species is Sminthurinus lawrencei although, strangely, whilst it appears on the checklist, it doesn't feature in the 'key'. It is usually grouped together with Sminthurinus niger in much the same way as Sminthurinus elegans is considered a variant form of Sminthurinus aureus.

It was effectively dismissed as a rare, somewhat questionable, form that had only been recorded from three countries, but the situation has now changed following recent research and discovery of the species elsewhere, including here in Britain. Prior to this research, it was virtually impossible to identify these similarly dark-coloured Sminthurinus species that lack any characteristic pigmentation from the available descriptions. The research concluded with a paper being published in December 2022 that provides the necessary material and results to confirm that Sminthurinus lawrencei is now a species in its own right and that it is very likely more common than Sminthurinus niger.   

Given their tiny size, there is no way that I would attempt to determine the species from photos. In fact, I would have thought it was impossible, but the reason that I've included the above detail is that a couple of the photos I posted to the UK Collembola group were identified as Sminthurinus lawrencei by Roel van Bezouw who was the lead author of the paper. In the past it has always been maintained that it is essential to closely examine these species to check fine details such as the subapical setae on the dens, so it was interesting to see that the paper makes very specific reference to the importance of good digital macro images and how they are becoming a valuable tool to assess the distribution of species, rather than focusing on characters that can only be reliably discerned under a compound light microscope.

Sminthurinus niger has traditionally been described as a small, maximum 1mm long, black or bluish-black globular species; with the fifth abdominal segment separate as opposed to having a wholly fused rear end as found in the aureus group; fourth antennal segment not subdivided; eye-patch comprising eight ocelli, often with a small white spot on the inner side.

The description for Sminthurinus lawrencei is now much more comprehensive with the main visual differences being that females may reach 1.2mm long, whereas males are approximately half that size; the head, body and appendages are all, invariably, uniformly grey-black, while the furca is pale; juveniles are lighter. The details regarding the eye-patch, and the facial, body and furca setae, are extremely detailed, but of little practical use when trying to identify the species from a photo unless, like Roel van Bezouw, you've seen enough specimens to pick up on subtle detail. In this respect, the focus is on the white inter-ocular vesicles, which for simplicity are referred to as the 'eye brows'. It is the size, position and relative shape that distinguishes the species, briefly confirmed as small, distance between 2x eye-patch diameter = S.lawrencei; circumventing the ocular field, distance between smaller than the eye-patch = S.niger; and, if they were noticeably large and set back, you'd need to consider the rare S.concolor, being another member of the Sminthurinus niger group.

A final observation from the research is that Sminthurinus lawrencei is more likely to be found above ground on dry surfaces, such as wood, bark or stones where there is shelter in the way of cracks and grooves. In less natural habitats it was regularly recorded from places like garden flowerpots. Sminthurinus niger on the other hand has always been described as favouring moss, moist leaf litter and soil.