Local dispersal and mating behavior of individually marked adult milkweed bugs (Lygaeus kalmii) were studied in a host patch of the milkweed Asclepias viridis in the tallgrass prairie of eastern Kansas. Over a four week period in July, immigration of bugs into the patch was roughly matched by mortality and/or emigration from the patch. Individual males and females visited similar numbers of plants in passing through the host patch, but females spent less time on each plant and dispersed through the patch more rapidly [median (maximum) number of days elapsing between first and last observations of individual bugs: females 1 (21), males 4 (20)]. The bugs spent much of their time in the patch mating (males: 28% of observations; females 41%). Individuals of both sexes mated multiply; individuals were observed mating with as many as six different partners. Mating success on an individual host induced males to remain there longer. Dispersal of females, however, apparently was uninfluenced by mating success