Haworthia arachnoidea var. nigricans leaves have characteristic bristles along the leaf margins, as well as on the keel (on the outer surface) below the leaf apex. These bristles gave cause to the spider reference in the name. H. arachnoidea leaves vary between 2 cm and 7 cm in length and are about 1 cm wide. The leaf shape is ovate to lanceolate and in-curved, the lower surface convex.
The plants usually form clusters. They produce flowers in various shades of orange.
(See many variations of this plant on http://haworthia-gasteria.blogspot.com/2008/09/haworthia-arachnoidea.html.)