Ballus chalybeius

subadult male in retreat

This flattened spider can reach a length of 3–4 millimetres (0.12–0.16 in). The prosoma is dark brown in females, with irregular lighter markings. The lightly yellow legs have dark rings in both sexes. In males, which are generally darker, the first legs are dark and thickened. The species is similar to Ballus rufipes, which is smaller and much darker.[1]

During summer, the female builds a flat silken retreat on the underside of a leaf and guards its egg sac inside.[1]

It can be found mostly on the fringes of deciduous forests, on broad-leaved bushes and trees, particularly oaks, and in the grass. In Central Europe, they are widely distributed and in most areas quite common.[1]

B. chalybeius occurs in Europe, North Africa to Central Asia.[2]

The species name is derived from Ancient Greek chalyb- "steel".

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