Hadrurus spadix is almost identical to H. arizonensis spare one major superficial difference. Hadrurus spadix has a uniformly darkened carapace whereas H. arizonensis has an area devoid of coloration that forms a "U" shape at the front of the carapace near the chelicerae and lateral eyes. This area between the three sets of eyes (two lateral sets of usually three eyes, on the anterior corners of the carapace; one median pair on the top of the carapace) is called the interocular area. In H. arizonensis the unpigmented area is within this "interocular crescent".

Other differences include the number of chelal trichobothria, very sensitive long hairs on the inside the pedipalp hands often vary in number, especially among Hadrurus and is an excellent character for the three American species and the other five in Mexico.