Seven species of carabid beetles were examined in different “pH-Orgeln” for pH-preferences. Five of these species showed significant preferences for specific pH-fields. Presumably, this parameter of distribution found in the laboratory is also effective in the field. We caught the beetles in the field on soil of the same pH-values which they prefered in the laboratory. The pH-measurements taken by previous workers in the field match our results.
The receptors for H-ions are probably located on the antennae, because the preference distribution of Pt. angustatus changed into a uniform distribution after amputation of the distal segments of the antennae. The structure of these receptors could not be identified in electron microscope pictures (REM) among the multitude of different receptors on the antennae.