Abstract: When a fly is in contact with a hard and smooth surface,the process involves the adhesion between the surface and the cilium of thefly legs. In this article, the contact problem is formulated under the JKRtheory. An expression of the adhesion force is derived with respect to thesurface energy. The bounds for the scales of the cilium thatenable the fly to adhere and to detach from a hard surface are estimated.These bounds are consistent with the SEM observation.