The deer flies,Chrysops atlanticus, are important pests of humans which move from the salt marsh and concentrate in wooded areas, especially along field edges. Studies at four sites showed that<2% of the deer flies attracted to a human host occur 50 and 100 m into the field whereas 64% were encountered at the field margin and the rest in the ecotone and on the salt marsh. No concentration of flies occurred where no vegetative barrier was present between the marsh and fields. More flies were taken in the morning than at noon and in the late afternoon during June and July near Cedarville, N.J.