February to May marks the months in which the eastern subterranean termites swarm. During this time, you may see flying termites or "swarmers" swarming in the day. You might also find wings by windowsills or dead termites on the ground. Formosan subterranean termites swarm at night during the late spring. Swarming is a sure sign that there is a termite infestation destroying your house unnoticed.