The surface shape of the distal asperity on the chelal moveable digit in thirteen free-living saprophagous astigmatan species is examined within the context of a cracking mechanism used in specialist ship designs. Twenty females of common macrosaprophagous and the larger microsaprophagous free-living astigmatan species were examined as cleared mounted slides under Nomarski differential interference phase contrast microscopy. Changes in moveable digit surface asperity shape were scored in detail. Species (and population code) used were: Acarus siro (A10B) and its SW variant (A15), Aleuroglyphus ovatus (AL2), Chortoglyphus arcuatus (CH1), Dermatophagoides pteronyssinus(D3), Dermatophagoides farinae (D4), Dermatophagoides microceras (D5), Glycycometrus hugheseae (G3), Glycyphagus domesticus (G5), Lepidoglyphus destructor (G6), Rhizoglyphus echinopus (R1), Tyrolichus casei (T62), Tyrophagus perniciosus (T8), and Thyreophagus entomophagus (TH3). Only in the acarid Acarus siro, and the two pyroglyphids Dermatophagoides farinae and Dermatophagoides microceraswas credible evidence that a mechanism other than cutting food material on chelal protrusion was found.