QUESTION:
Do subterranean termites have a typical depth they prefer? I’m sure moisture somewhat dictates their behavior, but are they mostly within five feet from the surface or something like that? I ask because products for defined treatments work so well, I hear, they must assume that the material has leached to a depth to ensure contact with termites coming from ouside a structure going underneath a slab or crawlspace ect.
ANSWER:
Well, I am going to give that lovely and worthless answer – “it all depends”. Looking through some resources on termites we can find a lot of variance in the answer to how deep their nest may go in the soil. In the Mallis Handbook of Pest Control it states that Reticulitermes flavipes (Easter Subterranean) may be found underground to depths of 5 feet. However, another reference in this book states that they will move up and down in the soil as needed to maintain contact with very wet soil, and possibly to stay near the water table below them. One internet reference states that they very much need wet soil for building their tubes, and for this reason may go as deep as necessary to reach the top of the water table. In some places this may be just a few feet below the surface and in other perhaps a hundred feet or more.
Other internet references use numbers such as 20 feet deep, or 10-20 feet deep, but I always wonder if many of these websites could simply be repeating the same accurate or false information, so that may not be definitive. One thing that does seem to be consistent is that the underground colony is not restricted to one place, but may move up and down in the soil as the environmental conditions dictate. As the soil above dries the colony moves deeper, and as it moistens or the water table rises the colony moves upward. Moisture is the key.
When we chemically treat the soil our goal is to place an unbroken layer of the chemical in the soil around or under the structure, ensuring that any termite attempting to get to the wood of the structure must pass through that chemical layer, and be exposed to it long enough to take in a lethal dose. It is NOT our goal to use termiticides that leach down into the soil to penetrate the nest itself, and in fact this would be a dangerous situation if our products did that. The chemical that leaches down through the soil also poses a high potential for ending up in the underground water tables, and from there into drinking water. Nearly all of our termiticides have very LOW water solubility, meaning they do not dissolve in water and thus will not flow where water flows. Instead, we apply them using water as the diluent and once the water dries the active ingredient ties up tightly in the soil particles and (hopefully) does not move from that location. For surface applied materials such as a pretreat this may be no more than a half inch deep in the soil. For trenching we place it deeper around the foundation so that any way the termite moves to the foundation it must pass through the termiticide.
This is the success of the non-repellent products that also have a good Transfer Effect. Any termites that find their way into treated soil could pick up enough of the active ingredient to pass it around to other members of the colony. Since foraging workers are constantly making this trip out of the colony and to a structure there is going to be constant contact with the termiticide as they close in on the treated soils above the nest. We rely on the termites themselves to make the contact rather than hoping our application breaks into the colony. The different families of chemistry offer different methodology for protecting the home. The old organophosphates relied on killing the termites that entered the treated soil. The pyrethroids rely a great deal on repelling the termites away from treated areas, but not necessarily killing them all. Newer chemistries are looking for the non-repellency and a slow acting kill to allow for the transfer of the active ingredient to termites that stay in the colony.
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