How Do Subterranean Termites Find Wood?

It’s not just a random search.


Editor’s Note: This article was reprinted with permission from Techletter, a biweekly training letter for professional pest control technicians from Pinto & Associates.

We often say that subterranean termites are not attracted to wood, but instead forage randomly until they find wood. This is somewhat true but it’s not as simple as all that. There are certain factors that influence where and how termites forage — some are environmental; some are chemical.

FORAGING TERRITORIES/PATTERNS. The foraging territory is centered around the termites’ underground galleries, and the size of that territory varies with the termite species, age of the colony, size of the colony and availability of nearby food. Some large subterranean termite colonies can forage over an area the size of a football field, but most colonies don’t forage over their entire range at any one time. While ants move back and forth from a feeding site to their colony, evidence indicates that termites act more like a herd of grazing animals as they move in groups from feeding source to feeding source. A colony’s foraging area can change in size and shape over a couple of weeks.

Foraging termites don’t simply set out from the colony in any old direction; instead, they create a system of branching, pencil-sized tunnels in the soil as they look for food. These exploratory tunnels expand out in a starburst pattern from a central point. This systematic and radiating search pattern of tunnels helps to eliminate repeat searches in the same area. There also is evidence that termites evenly divide up their search area with their tunnels. While not exactly random, this tunneling behavior ensures that the termites will find wood eventually.

Subterranean termites are helped in locating wood by their habit (like many other insects) of trailing along the edge of objects. Termites will locate and follow a building’s foundation or trail along pipes, conduits, pavement edges or root systems. They also will trail along the edge of brick veneer or hollow block foundations. Termites will follow these edges either underground or by constructing exploratory mud tubes. Often these paths lead directly into a building and a food source once they come across a crack or a utility opening.

ENVIRONMENTAL CUES. Daily foraging is influenced by weather factors such as temperature and moisture. Foraging activity tends to be the greatest in areas of higher soil moisture. Studies have shown that subterranean termites locate food sources by keying in on temperature/moisture shadows on the soil surface. In other words, termites in desert areas can detect areas of vegetation on the dry ground above and will forage more heavily in these sites, which tend to be damper. Thermal shadows also are cast by other objects such as logs, paving stones or a building. The soil profile (the percentages of sand, clay and silt) also affect termites’ ability to construct tunnels and forage.

CHEMICAL CUES. Termites also respond to chemical odors given off by plants and decaying wood, although they can detect these odors only from a short distance. We stop short of saying termites can actually find wood by cueing in on its presence. If that were the case, all in-ground bait stations would be hit right away.

As a termite forages, it secretes pheromones along the way. When a worker finds a new source of food, it returns to the colony, reinforcing the pheromone trail as it goes. The termite colony’s random foraging behavior now changes to a more structured recruiting and feeding behavior. Other termites follow the pheromone odor trail back to the food while laying down more pheromone. More permanent working mud tubes are constructed to establish a highway from the underground galleries directly to the new food source.

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