Mitopus morio var morio is a large, conspicuous and common harvestman but also extremely variable in colouration (especially the females). The male usually has a conspicuous black saddle on a light sandy background which is sharply waisted and often expands to the full width of the abdomen behind the saddle. (In others it constricts again to give a 'double-waisted' appearance). Sometimes all-black males occur. The saddle of the variable females normally has a slightly 'double-waisted' appearance. Sometimes the saddle of the female is delineated by a pale line and sometimes lightens towards the middle. Occasionally there is a light central median stripe. The ocularium is normally silvery and lightly armed with a few small tubercles. There is no trident but occasionally a few very small tubercles. Dark legs contrast with large pale trochanters.
Mitopus morio var ericaeus is, of course, very similar. Habitat is a good clue when separating them since M. morio var ericaeus is limited to moorland above 250 m (though M. morio var morio occurs there too and they are often found together). Mitopus morio var ericaeus usually has a very prominent median stripe and the outline of the mottled-pink saddle is well-marked with black and white. The ocularium of the male Mitopus morio var ericaeus is more prominent than that of male M. morio var morio.
A more common difficulty is separating females of Mitopus morio and females of Palangium opilio. These can be similar in size with a rather similar looking saddle. In general, the ocularium and armature of Palangium opilio is more robust. The saddle area around the eyes in Palangium opilio tends to be paler than the rest of the saddle whilst in Mitopus morio this difference is not so apparent. The real clincher is the presence, on Palangium opilio, of two small tubercles on the supra-chericeral lamella (between the edge of the cephalothorax and the top of the chelicerae), which are absent in Mitopus morio. Normally a hand lens and spi-pot are required to see these (occasionally, and with luck, they are visible in photographs).
Mitopus morio var morio is very widespread over the whole of the - see the distribution map of the Spider and Harvestman Recording Scheme . It is also found everywhere in Europe.
Mitopus morio var morio is extremely catholic in terms of broad habitat and micro-habitat, including all vegetational zones. It appears to be particularly common in upland areas.
Adults occur from late summer to early winter with a broad peak from August to October.
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.