The pilot reported that he was landing at a non-towered airport at night to drop off a passenger. During the landing flare just prior to touchdown, the pilot saw three deer run onto the runway out of his periphery. One of the deer ran on to the runway and was struck by the airplane's left main landing gear. The collision folded the left main gear aft and the left wing contacted the runway as the airplane touched down. The airplane slid down the runway and veered off the left side of the runway surface before coming to rest. Examination of the airplane revealed substantial damage to the left wing and aileron.