Optimisation and use of a device for the on-hen in vivo feeding of all hematophagous stages of Dermanyssus gallinae. The sealed mesh device contains the mites and is applied to the skin of the hen's thigh where mites can feed on the bird through a mesh which has apertures large enough to allow the mites' mouth-parts to access to the bird but small enough to contain the mites. By optimising the depth and width of the mesh aperture size we have produced a device which will lead to both reduction and refinement in the use of animals in research, allowing the pre-screening of new vaccines and systemic acaricides/insecticides which have been developed for the control of these blood-feeding parasites before progressing to large field trials. For optimal use, the device should be constructed from 105 μm aperture width, 63 μm depth, polyester mesh and the mites (irrespective of life stage) should be conditioned with no access to food for 3 weeks at 4 °C for optimal feeding and post-feeding survival.