The one-way spider. The markings of this crab spider appear to have an arrow-shape. Rationalisation for the name 'crab spider' generally is subjective and anecdotal. Some say it refers to a fancied resemblance to crabs, or to the way such spiders hold their two front pairs of legs, or their ability to scuttle sideways or backwards. The Thomisidae are the family most generally referred to as "crab spiders".