ARACHNIDA > ARANEAE > Thomisidae > Ozyptila and Xysticus

As previously noted, these two genera include most of the 'crab spiders' that have been recorded in Britain; 22 of the 27 species in fact.   

The Ozyptila species are collectively known as 'lesser crab spiders' due to their small size, which is typically around 3-4mm at most. Whilst they can only be reliably identified by microscopic examination, Ozyptila praticola is the only species regularly found in gardens. The description also matches the individual featured below; dark brown to black carapace with reddish central band, greyish-brown abdomen mottled with black, and brown legs with darker annulations. It's the only individual I've photographed, so at the moment I haven't looked too closely at the other nine species, but I have noted that they are generally associated with very specific habitats that can always help narrowing down possible candidates.

The Xysticus species have a similar squat, rounded appearance, but are somewhat larger, averaging around 8mm or so. They also have more definite body patterns than Ozyptila, although still come with the same advice in that they cannot be properly distinguished from photos and that any given identification is 'likely' rather than certain. This is the problem with so many species and the reason why distribution maps are so skewed if data is purely based on specimens that have been examined under a microscope. I guess that most arachnologists will only record species that have been properly identified, but fortunately there seems to be more acceptance that a 'likely' recording based on a photo also has merit and, certainly from a more casual personal point of view, a 'likely' identification is far more useful than just listing species by genus. If the FB Spider Group consistently stated that individuals could not be taken further than genus, I think I'd quickly lose interest, but they don't and, in many cases, are happy to confirm the most 'likely' species.

Xysticus cristatus is by far the most abundant and widespread species as it can be found in low vegetation in many open habitats, but rarely in shady places like woodlands, which in itself is a useful identification feature. It is pale brown with the dark triangular marking on the carapace ending in a well-defined point, and a distinctive abdominal pattern consisting of a broad central band bordered by darker rows of triangular marks that, from all the photos I've seen, look exactly like the individuals featured here.

Xysticus ulmi looks similar, albeit with slightly different markings that have a clear defining line between the dark dorsal pattern and the light ventral colouration, but again, the individual featured here looks exactly the same as the photo in my field guide. Xysticus ulmi also differs from other Xysticus species by having a more elongated abdomen. It is typically associated with low vegetation in damp, marshy habitats.

Xysticus kochi is a common, but regional species, most frequent in the south. It tends to favour more sparsely vegetated locations than the previous species, occuring in a wider range of habitats including occasionally in gardens. The likely identity of the individual featured below is based purely on appearance and comparison with verified photos.

Xysticus lanio is an uncommon, regional woodland species with the female having a very distinctive red appearance. The male is typically darker, but very variable and probably hard to distinguish.

The identity of the above-mentioned species has either been confirmed or deemed 'likely', whereas those captioned simply as Xysticus sp. are undetermined and cannot be taken any further, although I suspect that the individual photographed in Bradninch in damp pondside vegetation is probably Xysticus ulmi.

Updated, Jan.25 (v.5)