Although there are 47 different species of termites in the U.S., Iowa is fortunate to have only one species that consistently attacks houses and other structures, the eastern subterranean termite, Reticulitermes flavipes. Research on this termite has yielded the following interesting information.
Termite Demographics. Termite population studies in Canada and Florida have brought changes to our "best guess" about the number of termites you would expect to find in a termite colony. Earlier research had estimated termite colony size at about 60,000 individuals, but the new research finds populations to be much, much larger.
Termite populations are estimated by the same technique used by animal ecologists to measure bird or fish populations; that is, the mark-release-recapture method. First, several individuals from a population are captured and marked with a permanent mark, band, or dye. These are then released and allowed to disperse back into their environment. Some time later a second sample is collected that should contain both marked and unmarked individuals. A mathematical formula comparing the ratio of marked to unmarked animals is used to estimate the total population size.
Mark-release-recapture research on termites is accomplished by collecting thousands of live termites in rolls of corrugated cardboard buried in the ground. The termites are fed a harmless red or blue dye before they are returned to the trap site. Dyed termites will be pink or light blue in the subsequent sample. The dye is not passed to other termites.
The current population estimation for eastern subterranean termite is that colonies can contain up to 5 million termites. Research in Ontario Canada, the closest research to Iowa, found colonies of 2 to 3.2 million termites.
Territory Size and Foraging Distance. Workers from a termite colony constantly explore for food by randomly excavating small tunnels through the soil in the area surrounding its nest. The result is a large network of scattered, random, pencil-sized tunnels. The "nest" itself is nothing more than a loose collection of enlarged tunnels and chambers where the queen and/or secondary reproductives happen to be at the moment.
The population research described above included a sampling grid of pine stakes pounded into the ground to estimate territory size and foraging distance. By pulling the stakes and examining for pink or blue termites researchers were able to conclude that termites will forage for distances of up to 100 meters (330 feet) from their nest site. In addition, the termite workers will radiate out from the nest and end up foraging in a territory of 400 to 2,200 square meters. That is approximately 1/2 acre or 24,000 square feet that will be covered by a single termite colony.
In spite of rapidly progressing research on alternatives to traditional termite control methods, the only way to confidently protect your house from termite attack is to use a chemical barrier in the soil adjacent to the house to "exclude" termites. The size and foraging distance of termite colonies would indicate there is no such thing as a reasonable "spot treatment" for termites; that is, it is not reasonable to treat one side of an infested building because that is where you have seen the termites and let the rest of the structure go untreated.
Second, we may need to reassess our assumptions about risks to surrounding buildings when termites are discovered in one building. The risk to buildings in a termite infested neighborhood is very real when a single termite colony may be covering two or more standard city lots.
This article originally appeared in the April 8, 1992 issue, p. 52.