The underside of Opilio saxatilis, in common with that of O. parietinus, is very pale with brown irregular spots on the coxae - feature which separates them from all other harvestmen. The pale midline stripe is usually constant in Opilio saxatilis and has a slight kink in the middle of each segment giving an appearance rather like 'sergeant stripes'. The femurs of legs 1 and 3 can be markedly swollen, especially in the males.
Size is the first clue to separate Opilio saxatilis (up to 6 mm) and Opilio parietinus (up to 9 mm). The armature of the ocularium also provides good evidence, there normally being between 2 and 4 tubercles on the ocularium of Opilio saxatilis and between 4 and 8 on that of Opilio parietinus. If viewed with a spi-pot and lens, the genital operculum of the male is rather more flared in Opilio saxatilis (and it has a slight notch in the end) compared with Opilio parietinus. Unlike in Opilio saxatilis femurs 1 and 3 are hardly (or not) swollen.
Quite widespread in the UK but most common south-east of a line between the Severn and Humber estuaries - see the distribution map of the Spider and Harvestman Recording Scheme .
Much less synanthropic than the other two Opilio species, Opilio saxatilis can be found in a range of dry semi-natural environments including open woodlands, heaths, sand dunes and gardens. It can often be found on the ground at under rocks and wood. A good place to look is behind grass at the base of rocks, buildings, trees or posts. Coastal areas are often productive.
Adults occur in from late summer and well into the early part of winter with a clear peak in September.
Hillyard, P. D., & Sankey, J. H. P. 2005. Synopses of the British Fauna (New Series) No. 4: Harvestmen. Third Edition.Field Studies Council, Shrewsbury.
Richards, P. 2010. Guide to Harvestmen of the British Isles. Field Studies Council, Shrewsbury.
Richards, P. 2017. Tabular key for Identification of British Harvestmen (Opiliones). Unpublished.
Wijnhoven, H. 2009. De Nederlandse hooiwagens (Opiliones). Nederlandse Entomologische Vereniging.