If Ikea did invertebrates

Yesterday, whilst pottering to the garage to sort out the recycling ahead of this week's bin collection, I spotted a wee creature on the paved path at the front of the house. It was about 20mm long and my initial reaction on profile and colour was "centipede". Putting down the recycling out of the wind (I'm not making that mistake again!), I nipped back into the house for my phone and compact camera, the former to use ObsIdentify, the latter for better close-ups.

Phone photo for ObsIdentify

Compact camera set to Macro

A vaguely in-focus antenna

A pointy bum

ObsIdentify gave me a virtual eye roll and said "100%, it's a millipede from the Family Polydesmidae indet". Somewhat chastened, I recalled that I had previously photographed a flat-backed millipede in 2021, when we lived in Houton. I think this is the first one I have seen at Burnbank, but the "indet" means that arriving at an identity to species from a photo will be impossible. Looking at online keys, it seems that the millipede is probably of the Genus Polydesmus, but of the several species present in Scotland, it cannot be taken to species without recourse to dissection of the genitalia.

On several levels, this is not that sort of blog!

The internet further informed me that males have their genitalia (gonopods) in the space where the eighth pair of legs would be, whilst females have theirs (epigynes) behind the second pair of legs. As the millipede was constantly moving, the wave motion of the leg movements caused blurring of images, so depending upon which photo I looked at, the  gaps seem to change. How very gender unspecific of it.

Looking at the National Biodiversity Network (NBN) Scotland Atlas, there are Polydesmidae records for Orkney, 14 of them, dating from 1978 to 2011. These cover three species, Brachydesmus superus, Polydesmus angustus and Polydesmus inconstans.

The records are from the West Mainland and the island of Hoy. The only record from Stromness (where we are) is from 1978. The large oval dot is three records from Binscarth Wood near Finstown, whilst the dot south west of there contains two records from Happy Valley LNR in Stenness.

At 20mm long, "our" millipede was definitely a Polydesmus sp. as Brachydesmus superus is only around 10mm in length. But there the ID journey ends until I happen to find a recently-deceased one to examine.

Most millipedes are detritivores, they eat decomposing plant and animal matter. This is an essential ecological function which prevents the world being knee-deep* in decaying matter, by recycling nutrients and maintaining an ecological balance.

* human knee, rather than millipede knee