Termites: The Drywood Termite
One of the most damaging organisms to the integrity and value of our homes is the termite. Just discovering that we have termites eating our house is enough to cause great anxiety in us, because it generally is a huge mystery to us as to just how these critters got there, and even a bigger problem in how we are going to get rid of them.
In other BugInfo articles we have discussed some of the most important termites in the United States, the Subterranean and Formosan Termites, as well as a discussion on termite baiting and how it fits into a termite control program. In this article we hope you gain some insights into a different kind of termite called the Drywood Termite, so called because it does not have the need for moisture in the wood that the other kinds of termites do.
Drywood Termites are not nearly as common in the United States as are the dreaded Subterranean Termites. There are several different species of Drywood Termites, and they occur primarily in the warmer areas of the country, throughout much of California and Arizona, down into Mexico, as well as Hawaii, the Gulf states, and along the east coast. Florida, in particular, has several different species present. These termites can live in extremely dry wood, and have no need to maintain contact with the soil, increasing the difficulty of controlling them.
How do I recognize Drywood Termites?
Drywood Termites fall into a happy medium in size, somewhere between the tiny subterranean termites and the huge dampwood termites. Like all termites they are “social” insects, with a Queen who does all the egg laying, workers who tend the eggs and youngsters and who forage for food for the colony, and soldier termites who defend the colony from enemies. The soldier is equipped with large, sharp jaws, and even though it is blind it is very adept at snapping the jaws at potential enemies if these should penetrate the colony.
There also is a caste within the termite society called the “alate”, or the sexually reproductive adult termites that have wings. They fly from the colony to start new termite colonies in new places. In the Drywood termites these winged adults are reddish brown, and the wings have a slight brown tint to them as well. Like all other termites, once the “swarming” has taken place the alate loses the wings. They have no more use for them once they have begun a new colony inside the wood, so the wings are deposited outside so they won’t be in the way. You may find these wings lying around on your back deck or in a window sill.
Otherwise, if you happen to be remodeling and just tear open some wood – maybe a window sill or a door frame – you could, sadly, stumble upon a bunch of the small, soft, white workers moving up and down inside the hollowed-out galleries in the wood. You might also find one more sign of the Drywood termites, and that is their fecal material. In fact, this is usually what professional termite control inspectors look for when they are inspecting a home, because the Drywood termites regularly push all this junk out of their colonies. It may take a couple of years for the new colony to be in existence, growing and increasing in numbers, before the workers start tidying things up, but eventually they realize that their hollow highways inside the wood look far too much like toilets, and some housekeeping is in order.
So, they chew a little opening to the outside of the wood, which we call a “kick hole”, and push all the small, dry, hard fecal pellets out, allowing them to fall to whatever surface is below, and a little pyramid of feces begins to develop. These pellets are distinctly grooved, which you can see if you look at them through a magnifying glass. Their color will be dependent upon the material they have been eating, and since Drywood termites will eat anything that is – or WAS – wood, the food could be wall studs, furniture, cribbage boards, newspaper or cardboard, or picture frames.
How do I keep from having Drywood Termites?
This can be difficult. Since these termites usually begin their colonies in the wood by flying to the structure, you have a very tough time keeping them from arriving. Subterranean termites must enter a structure from the soil below, and therefore it is a more cut and dry process for keeping them out by placing some sort of barrier on the soil. However, in recent years there have been some advances in preventing infestation by Drywood termites, and this is by spraying as complete a layer of chemical on the unfinished wood as you can.
A lot of the wood used in structures, particularly wood that may be in contact with the soil, has been “pressure treated” with chemicals that are toxic to the insects or fungus that tries to eat it. This treatment generally leaves a green color on the wood, and makes it a bit unsightly if it is in a visible area, or a problem if it is to be finished in some way. However, there are several formulations of “borates”, which are naturally occurring chemicals that are derived from borax, a mineral dug from the ground. Another of these that you might know of is boric acid, and all of these materials are toxic to bugs (or animals) that eat them. Fortunately, the amount of borate that a bug needs to consume to kill it is far, far less than it would take to harm people or pets, so we can spray very dilute solutions onto wood to prevent termites from chewing into it.
There also have been desiccating dusts that could be dusted into attics or wall voids, coating the bare wood there to kill insects that crawl around on it. This can get pretty messy, and these dusts really have given way to the borates in the past decades. Otherwise, there really are no repellents or other magic barriers to keep from possibly having Drywood termites choose your house as their landing pad on some warm spring day. One word of caution is probably prudent here – don’t waste your money on “ultrasonic” insect repelling boxes, that promise to keep away all manner of pests. They simply do nothing to affect the presence of insects, since the insects don’t hear them anyhow.
What about certain types of wood they won’t eat?
Many species of wood have some amount of “natural” repellency to them, but this is by no means a guarantee that the hungry termites won’t go ahead and settle for whatever is available. Redwood is one good example of a wood that is not preferred by termites, but it is the “heart” redwood, from the inner area of larger trees, that is the most repellent in taste, as it is this area of the tree that fills with chemicals produced by the tree. With less and less “old growth” redwood being harvested now, there is less lumber with the repellent qualities to it.
Termites probably prefer softwoods, such as pine or fir, but they are commonly found in hardwoods too, such as oak or walnut. Cedar has some strong odor qualities to it, due to its chemical makeup, and often it can be somewhat resistant to attack by termites. However, “resistance” does not mean “immunity”, and termites definitely will feed on and recycle cedar, along with pretty much any other kind of wood.
If I have Drywood Termites, how do I get rid of them?
Eliminating Drywood Termites really is a job best left to licensed professional pest control companies. The tools and chemicals needed are generally unavailable to homeowners. In general, there are two options for ridding your home of Drywood Termites:
- “local” treatment of just the wood you know is infested
- “whole house” treatment of the entire structure
In the years beginning in the 1980’s there have been some interesting advances in Drywood Termite control, as efforts have been made to find alternatives to the traditional “toxic” chemical approach to controlling pests. I won’t spend a lot of time on these alternatives because at this time there still needs to be independent, university-sponsored testing of these methods to see if they truly do control the termites without causing other possible problems.
Some of these alternatives include:
- heating the entire house to a temperature sufficient to kill the termites within the wood
- freezing selected wood members with liquid nitrogen
- microwave energy directed at specific sections of the walls or attic
- electricity directed into the wood with high-voltage devices
Since these methods have not involved the use of “chemicals” there originally has been no government scrutiny of their effectiveness, but many states are now requiring that such studies be performed to ensure the public is getting what they are promised.
However, traditionally the best method for eliminating Drywood termites has been to cover the entire structure with an airtight tarp, and introduce a toxic gas – a “fumigant” – into the structure. This fumigant has the ability to penetrate into all the wood to kill the termites hidden inside. Let me help you understand this process better, as well as its limitations.
Two principle fumigants have been used for this pest for decades now, and these are methyl bromide and Vikane (sulfuryl fluoride). Methyl bromide has recently fallen out of much use due to environmental restrictions on it, but Vikane remains the number one choice. It penetrates the wood very well, kills all the termites present very well, and ventilates quickly out of the wood to leave no toxic material behind for you, once you are allowed back into your home. Very strict guidelines are in place by both the regulatory agencies and by Vikane’s manufacturer, Dow AgroSciences, to ensure the proper procedures are undertaken.
What should I expect from a fumigation?
If Vikane is used you will need to be out of your home for just over one day. Preparation for the fumigation involves removing plants and animals from the house, as well as placing many household items such as foods or medications into sealed bags (or removing them from the house). The tarps are placed over the entire house, the fumigant is introduced, the termites are killed, and the next day the tarps are removed. At this time the licensed fumigation experts will enter the home with detection equipment, and very carefully inspect every area of the home to ensure all the fumigant has ventilated out of it. They will even check inside walls, furnishings, and appliances to make sure no gas pockets are trapped.
Vikane kills the termites very well, but does not kill the eggs well, which methyl bromide does. However, methyl bromide is much more restricted now, so it is not the better product for Drywood Termites. Since the baby termites that hatch from the eggs cannot survive without the care and feeding from worker termites, if all the workers have been killed by the fumigant these new baby termites will quickly die, leaving you with a home free and clear of the destructive little buggers. Since the gas dissipates completely, there really is no protection left behind by it, and other steps might need to be taken to prevent future termite invasions, but for the moment at least you have a home where all the termites are killed. Also, as a bonus, any other bugs or rodents you might have had in the house are killed to, so sayonara to silverfish, wasps, or mice.
What about “local” treatments?
If you are absolutely convinced that the Drywood Termite invasion you have discovered is limited to just a small area or single section of wood, then treating just that area with chemicals is an option. However, since the Drywood termites often have relatively small colonies, and there may be many colonies in a single structure, you just may not be aware of the other hidden infestations yet. Even subterranean termites may have multiple, entirely separate colonies all working at the destruction of the same building, as studies in California have shown recently. A small home was found to have at least 8 separate colonies of these soil-dwelling termites feeding within it.
Since the social termites construct “galleries”, or hollow pathways inside the wood, and they move back and forth through these galleries doing their daily duties of infant care and shopping for food, it is possible to expose them to toxic chemicals by injecting the material into the gallery. There are several products used by the professionals, and they will definitely work well, but not as well as whole structure fumigation. Usually, the choice to do a local treatment is determined either by the financial situation of the homeowner, who perhaps cannot afford the fumigation, or by the setting of the home, where it cannot physically be tented. This happens a lot in San Francisco, or perhaps other downtown environments, where homes along a block are all pretty much linked together, and one cannot be separated for treatment.
Obviously, treating just the galleries of the Drywood termites infesting a door frame by the back door will not affect the Drywood termites infesting some 2 x 4 rafters in the attic, if they are a separate colony. For this reason licensed companies who end up choosing local treatment as the control option are not likely to offer much of a guarantee for the home. They would be guaranteeing something they really had no control over.
So, we hope this helps you better to understand Drywood Termites. On the plus side, since they have small colonies and they do not introduce moisture to the wood, as the subterranean termites do, the damage done by the Drywood Termites works slowly. It takes years of their activity to cause appreciable damage and structural weakening to the wood, in contrast to, let’s say, the Formosan Termites, that can literally destroy a home in less than one year.
But, however slowly the Drywood Termites are working, working they be, and it’s not the best thing in the world for your largest financial investment to have insects eating it. If you are in an area where Drywood Termites are prevalent it might be a good idea to keep your eyes open, to inspect the attic and the crawlspace occasionally, and perhaps bring in a licensed termite inspector to train his eyes on your home too, to see what creepy crawlies are there.