Abstract Counterfactual checks are made if the apparent trophic distinctions in the cheliceral whole moveable digit profiles of bird nest inhabiting free-living sarcoptiform astigmatans (Arthropoda: Acari) could be due to shared classification (‘ancestry’) rather than nidicolous characteristics. A novel gradualist multidimensional contrast-based method ( QUADLENG ) is presented in detail and calibrated to dissect the ecomorphology. Overall moveable digit profile designs of common acarids (represented by various Acarus species and Tyrophagus species) are often conserved at the genus level independent of any nidicolous habit. Size and taxonomic family matters in the trophic diversity of common forms. Between genus differences are dominated by the aspect ratios of trophic structures (such as the velocity ratio of the chela and the apparent shape of moveable digit teeth and gullets). Acarus farris (Oudemans, 1905) population A17, Acarus immobilis Griffiths, 1964 population A1 and most of the Tyrophagus spp. colonising bird nests represent just adventitious general saprophagous forms. Tyrophagus putrescentiae (Schrank, 1781) population T13 is confirmed as unusually designed. The out-group taxa Tyrophagus brevicrinatus Robertson, 1959 population T89, Tyrophagus perniciosus Zakhvatkin, 1941 population T38, Tyrophagus tropicus Robertson, 1959 population T90 and particularly Tyrophagus neiswanderi Johnston & Bruce, 1965 population T6 have distinct non-nidicolous moveable digit profiles. Some evidence of an astigmatan ‘economic pest’ design is found. Moveable digit forms suitable for possible ‘scratching’ and ‘scooping’ are found. Only the moveable digits of Acarus gracilis Hughes, 1957 population A4 and Dermatophagoides pteronyssinus (Trouessart, 1897) population D3 within their genera have unique derived nidicolous forms.
Clive Bowman (Mon,) studied this question.