Ophrys mammosa is a robust plant growing up to 70cm in height. Each lax inflorescence carries up to 18 flowers. The sepals and petals are olive green marked with brownish-red but the two lateral sepals are distinctly bi-coloured, the upper part being green and the lower a dark red. The lip is usually a dark brownish-red and occasionally has a yellow margin. The shiny speculum can be H-shaped, or consist of two vertical stripes which are parallel to each other.