Flight activities of two sympatric termite species, Macrotermes gilvus (Hagen) and Macrotermes carbonarius (Hagen), were studied in Penang Island, Malaysia. Herein, we present the first documentation of chronological reproductive isolation of M. gilvus and M. carbonarius. Flights of M. gilvus were recorded over a remarkably long 7-mo period from March to September, whereas swarming of M. carbonarius took place from November to January. Swarming events of M. gilvus and M. carbonarius occurred under atmospheric pressures of 1,005–1,011 and 1,006–1,010 hPa, respectively. Most flights of M. gilvus occurred on days with rain, whereas M. carbonarius avoided rain. Flight activity of M. gilvus was correlated significantly with atmospheric pressure and rainfall. The threshold temperature and relative humidity of M. gilvus flights were between 23 and 26°C and 83 and 98% RH, respectively; M. carbonarius swarmed between 25 and 30°C and 72 and 83% RH, respectively. The flight activity of M. gilvus concentrated in the warmer and humid months with a monthly total rainfall of 228 mm. Both species swarmed at distinct times of day during the limited field observations: Flights of M. gilvus began between 0300 and 0430 hours (light intensity <1 Lx), and flights of M. carbonarius lasted for only 4–10 min between 1900 and 1910 hours (at dusk; light intensity: 20–200 Lx). Windless conditions were preferred for the flights of both species.