The dispersal movement along with populational fluctuation, activity hours, and effect of abiotics factors of screwworm fly, Cochliomyia hominivorax, were studied at the Parque Natural Metropolitano (PNM) from September 1996 to April 1997. Screwworm fly activity was monitored using liver-baited station at three collection sites, two inside and one in the border of the forest. Temperature and wind velocity were registered at the time a fly was captured. 305 flies were captured in 74 d. (3.1 ? 5.33 flies per day). More flies were collected significantly during the dry season than the rainy season. Capture mean temperature and wind speed were 29.7 ? 2.2ºC and 0.47 ? 1.51 Km/h, respectively. Mean temperature was positively related and precipitation was negatively associated with the fly number. More flies were captured significantly at the site 2. Flies activity was higher at morning from 10:00 to 11:00 a.m. with other little peak from 3:00 to 4:00 a.m. 27 of 305 flies were recaptured at which the site it was higher. This site contributed with great amount of the flies to the others sites. Our results point out a low populations of these flies at the PNM. Probably, this fact is related to the wild mammals movements and habitat feature in this area.