Scanning electron microscopy observations of the distal leg region of the poultry red mite Dermanyssus gallinae (De Geer 1778) identified the presence of a compound ambulacrum, the part of the leg that contacts the substratum when the mite walks. The ambulacrum is comprised of a praetarsus (the ambulacrum stalk), a pulvillus and two claws. The pulvillus is a weakly sclerotized structure that can be partly expanded or retracted in the praetarsus. When expanded, the pulvillus shows a cushion-like shape which can, as a result of its soft surface, function as a sucker, thus allowing D. gallinae to adhere to a smooth surface. When traversing an irregular surface, or clinging to a soft surface, the mite retracts the pulvillus and uses only its strongly sclerotized movable claws. These observed morphological adaptations explain the ability of D. gallinae to climb upwards on a slippery surface, resist an air flux, walk on smooth and rigid feathers of its avian hosts, and cling to the bird's or human's soft skin. This knowledge is important to better understand the attachment mechanism of this species to its host and to the substratum on which it moves, and also to provide insight into the circumstances under which it is able to move. RESEARCH HIGHLIGHTS The ambulacrum is the distal part of the leg touching the substratum D. gallinae's ambulacrum consists of a praetarsus, a pulvillus and two claws The weakly sclerotized pulvillus can be part expanded/retracted in the praetarsus The expanded pulvillus functions as a sucker to adhere to smooth surfaces The claws are used to walk on an irregular surface or cling to a soft surface.
Keywords: Poultry red mite; ambulacrum; claws; functional morphology; leg adaptations; pulvillus; scanning electron microscopy.