Notes on Scotophaeus blackwalli

The Mouse Spider, Scotophaeus blackwalli, is a familiar inhabitant of homes and gardens, but there is a fly in the ointment. There is a second species of Scotophaeus in the UK, S. scutulatus. However, although widespread in Europe, this is very rare in the UK with only three British specimens recorded. The snag is that its close similarity to S. blackwalli means that other specimens may be overlooked. Thus, I feel morally obliged to check every Scotophaeus I see. Because Mouse Spiders are furry, it's difficult to get a good view of the epigyne without killing them, and as they are so common, that's a problem. Having been sent several Scotophaeus to I.D. today, I have been working on a better way of checking that works on live specimens.


Female Scotophaeus blackwalli

Scotophaeus blackwalli has 3 dorsal spines on femur III & IV (small juveniles may lack the diagnostic distal spine).
Scotophaeus scutulatus has 2 dorsal spines (proximal and median, no distal spine) on femur III & IV.

So telling them apart is "easy" - just look at the spines:


Male Scotophaeus blackwalli: P - proximal spine; M - median spine; D - distal spine (absent in S. scutulatus); S - scutellum (from the Latin for "shield"), an abdominal chitinous plate only present in males - is this for additional protection during mating?


I am indebted to Simeon Indzhov for his patient advice :-)