ARACHNIDA > OPILIONES > Phalangiidae > Oligolophinae

Mitopus morio, commonly known as the Saddleback Harvestman, is a distinctively marked, long-legged, larger bodied (females up to 8mm, males a little smaller) species with extremely variable colouration (particularly in the females) ranging from pale brown-grey through to dark chocolate, or even orange-pink. A darker form [var.ericaeus] also exists, but can be discounted locally as it's a moorland species only found at higher altitudes. The species described here is the nominate form [var.morio].

The males have a more consistent appearance with a conspicuous dark chocolate-brown to black, sharply waisted saddle on a light sandy background. The saddle typically widens behind the 'pinched waist' sometimes expanding to the full width of the abdomen. In some individuals though, it may constrict again giving it an almost 'double-waisted' appearance, not dissimilar to the females. The colour of the coxa and trochanters (leg bases) usually matches the background colour of the abdomen.

The female's saddle is narrower and rather variable in shape, but typically with a slightly 'double-waisted' appearance as it narrows before becoming wider at the centre and then narrowing again. The final portion is sometimes described as having a zig-zag edge. The colour of the saddle is also variable as previously noted and is often delineated with a black and then pale line. A median stripe may also be present.

They have dark, although again variable, coloured legs that contrast with the pale trochanters. The ocularium is pale and lightly armed. There is no trident.

Although the species is distinctive, females are very difficult to separate from the females of Phalangium opilio as both are of a similar size and often with a rather similar saddle. The important distinguishing feature is that on Phalangium opilio there are two small tubercles between the edge of the cephalothorax and the top of the chelicerae, which are absent in Mitopus morio. They are hard to see though and only occasionally visible in photos unless the character is known and focused on, which is easier said than done, so there are inevitably going to be many situations where the female of this species is going to be 'likely' rather than certain. There are a couple of other features to check, as noted on the Phalangium opilio species account.

Mitopus morio is regarded as one of our most common and widespread species, frequently seen in many countryside habitats. That's certainly not my experience, but that's probably because I'm not giving harvestmen enough attention. Adults occur from late summer to early winter, peaking in August and September at much the same time as many other invertebrate species. It's a busy time of the year when you need to be out almost every day.

Footnote: in putting this page together, I realised that I only had the one confirmed photo of a male (with red mites) and a few shots of questionable females which following closer scrutiny had to be relabelled as Phalangium opilio.  These particular photos had been filed before I started looking at the important identification features of these species and, consequently, before I picked up on the fact that the appearance and structure of the ocularium is very different. Here, in Mitopus morio, it's relatively smooth with just a few small tubercles, whereas in Phalangium opilio it's much more robust with two rows of between six to ten larger, acute, black-tipped tubercles. It's a really useful feature for separating females because, although the actual details may be difficult to see in photos, you can usually tell whether the ocularium is well-armoured, in which case Mitopus morio can be ruled out.