ARACHNIDA > OPILIONES > Phalangiidae > Opilioninae

Opilio canestrinii is a distinctive, sexually dimorphic, medium-sized harvestmen with very long legs.

The males have a shorter, more compact body averaging around 4-6mm long, which is much plainer than that of the female, with a more uniform orangey-coloured appearance and poorly defined saddle that may or may not have a few pale transverse bars across the abdomen.

The females are usually a couple of millimetres longer, with a more extended body that may reach 8mm long. They are a tad darker, usually orangey-brown, but sometimes more red-brown, typically with two rows of paired light and dark contrasting transverse bars across the abdomen, which are partially broken either side of a broad central band. However, just from my limited experience, I've seen that this species is quite varied with noticeably different markings from one individual to another with the colour of the transverse bars ranging from creamy-white and black to orange and brown, or actually non-defined and virtually blending in to a darker background.

I'm also confused about the colour of the legs as the FSC Identikit guide confirms that they are often very dark, almost black and, from the associated knowledge-base, they don't have any annulations. Yet, from other sources, they're confirmed as being dark brown, sometimes light brown, and ringed alternatively with light and dark bands The latter description definitely appears more correct.

Because their legs are very long, there is potential for confusion with Leiobunum species, particularly with the males, but a key difference is the colour of the trochanters. As previously noted, both Leiobunum rotundum and blackwalli have predominantly dark-coloured trochanters with some pale patches, whereas in Opilio canestrinii they are uniformly pale and contrasting sharply with the dark femurs.

The ocularium of Opilio canestrinii is also very different being quite small and flat rather than pronounced.  Although difficult to see in most photos there are two rows of small black-tipped tubercles. The ocularium itself is an orangey colour much the same as the body, often much paler around the eyes.  

Opilio canestrinii is a non-native species, first recorded in Britain in 1999 since which time it has spread rapidly to a point that it is now regarded as common in most areas. It is primarily synanthropic, more likely to be encountered in urban habitats, particularly gardens and parks, where it is frequently found on walls and tree trunks or in low vegetation. It also occurs in semi-natural woodland and obviously in other habitats given that I found one in woodland at a local heath. Adults are known to be active from July to November, possibly into December, but with the greatest numbers being recorded in August and September.