Marpissa muscosa, sometimes also called Fencepost Jumper, occurs mostly under loose bark on trees but also on fence posts, hence its English name.
Females are distinguished from the males by their orange coloured stripe under their front eyes.
Females reach about 8–11 mm length, males only 6–8 mm.

At my boathouse, Loosdrecht, The Netherlands, 8 September 2013