The weaver ant, Oecophylla smaragdina (Hymenoptera: Formicidae), is a successful predator and repellent of a range of insect pests of many economically important crops and forest trees. To use the ant as a biocontrol agent, extension officers and farmers need to know the best time of day to identify and transplant the ant colonies and to measure the abundance of the ant. To answer these questions, it is important to know about ant activity over a 24-h period at the colony level. Ant activities of three weaver ant colonies on the Tiwi campus of Charles Darwin University, Darwin, were measured in both dry and wet seasons in 1997 and 1998. The activity patterns on three types of ant trails showed that ants were least active between the hours of 10:30 and 14:00, and their activity peaked between 16:00 and 21:00h. There was also a smaller activity peak from 8:00 to 9:00h. The best time of day to identify ant colonies and to measure ant abundance is from 16:00 to 21:00h (late afternoon to dusk). The best time to transplant weaver ant colonies is between 10:30 and 14:00h (midday).