Termites are social insects that pose a significant threat to wooden structures because they continuously consume cellulose. Their activity cycles are complex, governed by the colony’s needs and external environmental conditions. Understanding termite activity requires clarifying the difference between constant, hidden feeding, which causes damage, and highly visible, temporary swarming, which indicates reproduction and colony expansion. This distinction separates the year-round threat from the seasonal warning sign.
Constant Threat: The Distinction Between Feeding and Swarming
The worker caste makes up the vast majority of a termite colony and is responsible for foraging and constructing tunnels. Workers relentlessly consume wood, making their feeding activity a continuous, year-round process within a structure. Because they operate in dark, protected environments like soil, wood galleries, or inside walls, their destructive behavior is rarely visible. This hidden activity means structural damage progresses constantly, independent of external seasons.
In contrast, swarming is a reproductive event where a mature colony produces winged adults, known as alates or swarmers. These individuals emerge in large, synchronized groups for a brief period to mate and establish new colonies. The swarmers themselves do not cause structural damage, as their purpose is purely to propagate the species. Seeing a swarm is a strong indication that an established colony has been active nearby for several years and is ready to expand.
Seasonal Activity of Major Termite Species
The timing of visible termite activity, specifically swarming, varies significantly based on the species and regional climate. Subterranean termites, the most common and destructive group, typically swarm after winter when temperatures begin to rise. In temperate regions, the peak swarming period for Eastern subterranean termites is late winter through early spring, often between March and May. Swarming can occur nearly year-round in warmer climates.
The Formosan subterranean termite tends to swarm slightly later, typically from late April through June. While many subterranean species swarm during the day, the Formosan species is known for its dramatic evening swarms. These swarms begin at sundown and end before midnight, often attracted to bright lights.
Drywood termites do not require contact with the soil and exhibit a different seasonal pattern. Their swarming activity is observed much later in the year, peaking in the late summer and early fall, often from August through November. Certain drywood species swarm during the day, while others may swarm at night. Dampwood termites, found in high-moisture environments, usually swarm in the summer months, sometimes extending from late spring into the fall, closely tied to consistent high humidity.
Environmental Triggers and Daily Activity Cycles
While seasonal timing is a guide, the exact moment a swarm occurs is dictated by immediate environmental triggers. Temperature is a primary factor, with consistent daytime temperatures often needing to exceed 70°F to initiate subterranean swarms. This warming trend signals that conditions are favorable for the survival of new reproductive pairs.
Moisture is another immediate trigger, especially for subterranean species that rely on damp soil to establish new colonies. Swarming events are frequently observed immediately following a warm, soaking rain, which provides necessary high humidity and soil moisture. High relative humidity, sometimes above 80%, is often required to prevent swarmers from dehydrating during their dispersal flight.
The daily activity cycle for swarming is species-dependent and often tied to light levels. Most native subterranean termites are diurnal, swarming during daylight hours. Conversely, the Formosan subterranean termite is nocturnal, emerging only after sunset and swarming toward artificial lights. This difference in timing helps prevent interbreeding with other nearby termite populations.
The influence of these external triggers is largely negated for worker termites that are already established inside a climate-controlled structure. When a building is heated and humidity levels are regulated year-round, the worker caste can continue to forage, tunnel, and feed without interruption from external weather changes. This is why damage-causing activity is constant, even though visible swarms remain a seasonal outdoor event.