Steatoda grossa has a body length when mature of around 10mm for adult females and again males are generally smaller. It is variable in appearance, with only juveniles and adult males usually having a pattern and adult females often having none.
The Steatoda grossa spider is also known as the false widow spider. They belong to the genus, or group, called Steatoda of which there are six species found in the UK including one introduced species, Steatoda nobilis. This group of spiders get their name because they look similar to the true black widow group of spiders, genus Latrodectus. In the UK two species are commonly mistaken for black widow spiders. They are Steatoda bipunctata, or the rabbit hutch spider, and the one that most resembles the black widow species, Steatoda grossa.