During May and June 1970–79, ca. 300–730 box traps painted with light or dark colors were placed around the perimeters of Cape Cod salt marshes to capture green head flies (Tabanus lineolaandT. nigrovittatus) which emerge during July and Aug. Yearly fluctuations in the average counts from a sample of 33 box traps visited weekly, generally correlated with average counts from unpainted, adhesive-smeared, square, masonite traps located at 6 sites in the experimental and 2 sites in the control marshes. These data and annual counts from ca. 40 additional box traps indicated that trap catches were related to annual variations in greenhead populations, marsh size, random movement of flies, and weather conditions rather than to the box trap colors. Over the 10- yr. period, a noticeable and measurable decrease in the nuisance level of the flies occurred around the perimeters of all marshes containing box traps. Samples ofTabanustaken from the traps were identified as 95.9%T. nigrovittatus)females, 3.6%T. lineolafemales, 0.4%T. lineolamales, and small numbers ofT. atratusfemales,T. nigrovittatusmales, and other T. spp. None of the trapped femaleTabanuswhich were killed and examined internally contained blood in the digestive tract, and almost 100% were parous. A list of other insects found in the box traps is given.