Philodromidae, also known as philodromid crab spiders and running crab spiders, is a family of araneomorph spiders first described by Tord Tamerlan Teodor Thorell in 1870. It contains over 600 species in thirty genera. Most are dull colored- brown, gray, yellowish or mottled with a leaf-like cardiac mark on the anterior dorsal abdomen, and seldom reach above 10 millimetres (0.39 in) long. None of the species build webs, but they do use silk for draglines and egg sacs.

It is superficially similar to the "true" crab spiders, such as Misumena vatia, but these families are not as closely related as previously thought. Philodromids tend to have few true setae (hairs or spines) on their bodies and lack the congruent eye tubercles of some crab spiders. Their second legs are usually the longer of the four pairs of walking legs. It is most evident in Ebo, where the second pair of legs are twice as long as the first pair in some species.

The most common genus is Philodromus which is widespread, similar to Ebo. Other common genera include the elongate grass-dwelling Tibellus and the widespread Thanatus, which includes the house crab spider that commonly captures flies on and in buildings.

Source: Wikipedia, the free encyclopedia