CHILOPODA (centipedes) > GEOPHILOMORPHA (soil centipedes) > Geophilidae

Geophilus flavus may look superficially similar to the previous described species Geophilus osquidatum at first glance but, as you start to appreciate the difference in size and general proportions, it can usually be determined even before you do a leg count. Fully grown adults may reach 45mm, considerably longer than any Geophilus osquidatum that are said to have a maximum length of 30mm. I'm sure that many individuals will be smaller, but anything around the 35-40mm mark will certainly indicate Geophilus flavus. They also look a bit chunkier, being in the region of thirty times longer than broad compared with the much slimmer Geophilus osquidatum that has a ratio of around forty to one (see footnote).  They're much the same pale washed-out yellow colour with a darker orangey-red head area, and both species have noticeably long antennae with elongate segments.

So that brings us to the all-important trunk segment and leg pairs. The 'key' indicates a fair range with males having 49-55 and females 51-57, which would overlap with the lower number for Geophilus osquidatum. However, the scientific survey that was undertaken a couple of years after the 'key' was produced, found that the actual number of leg-bearing body segments was lower for the British Isles than for north-western Europe. The associated data confirmed 47-51 for males (a smaller range and less than the numbers stated in the 'key') and 49-55 for females (again one segment less than the 'key'). Obviously, I have no idea how representative those numbers truly are, or indeed how useful seeing that I'm unlikely to determine the sex, but they do provide an overall range.

The next interesting point is that Geophilus flavus is considered to be a common and widespread species occurring in a wide variety of habitats, yet the current distribution data for the species doesn't show a single record from Dorset or, in fact, from anywhere in the wider south-west area. Very strange!

Footnote: the previous account for Geophilus osquidatum was written a couple of months prior to finding the two individuals featured here. At that time, I obviously had no personal experience or photos of Geophilus flavus, so was reliant on the information provided in the 'key' and the feedback from the BMIG FB group. I can now make my own comparisons and can see the difference between these two species. Individuals may vary and, in some cases, they may be more difficult to distinguish, but the Geophilus osquidatum specimen I photographed measured just 26mm - they don't grow much bigger - and has 61 pairs of legs which, according to the 'key' determines it's a female. The two Geophilus flavus specimens below both measured around 35-40mm and have 53 and 51 pairs of legs respectively which, doesn't determine the sex, but that's not important as the useful data here is the size and leg count. I can now see that Geophilus osquidatum is far more slender. The 'key' confirms an overall length to breadth ratio of about 40:1, which seems about right and makes sense given that they have more legs on a shorter body. Geophilus flavus on the other hand, has a lower ratio that is nearer to 30:1 as confirmed above, which again makes sense as it has fewer legs on a longer body. When I look at all these facts and comparisons, I'm even more convinced that I've separated these species correctly.