Image Dr. Kaae.                                                                                                                                                                                                                                                     

Termites are true social insects. They not only live in colonies, but divide labor so that different forms or castes carry out prescribed duties for the good of the entire colony.  No individual termite can survive alone.  These insects can be considered beneficial or harmful depending upon one’s frame of reference.  Worldwide, they are extremely beneficial as decomposers of dead trees, leaves and other sources of cellulose. On the other hand, they are major pests on agricultural crops, forest nursery seedlings, rangeland grasses, stored products, and household furniture. Most importantly, they are of extreme importance as structural pests worldwide.

Biology. From an evolutionary standpoint these insects are considered somewhat primitive, but social organization is well developed in termites.  Along with ants and the more highly organized bees and wasps, they belong to the truly eusocial insects.  The common traits of eusocial insects include the following: 1. Cooperative caring for the young.  2.  A division of labor with different forms carrying out different functions for the overall good of the colony.  3.  An overlap of at least two generations so that at some point the offspring can assist their parents in colony development.

By necessity in order to develop colonies, social insects must be long-lived.  One of the limiting factors to accomplish longevity is a continuous source of food.  Of course termites feed on one of the two most common sources of food in the world, namely plants (as opposed to animals) or, more specifically, cellulose. 

The 2 major families of termites in the United States are Kalotermitidae (drywood termites) and Rhinotermitidae (subterranean termites).  Both depend on protozoan in their hindguts to digest cellulose. Termites do not possess these protozoa at birth but acquire them by proctodeal feeding or more simply feeding on fluids from the anus of mature individuals.  Because the lining of the hindgut (including the protozoans) is shed with molting, newly molted individuals reacquire the protozoans by proctodeal feeding. This feeding activity by termites in general (including feeding from another termites mouth-stomodeal feeding) is referred to as tropholaxsis.  It is the main means of communication between termites in a colony.  It has multiple functions including efficient use of nutrients, recognition of nest mates, distributions of chemicals involved in caste regulation and as previously indicated the transfer of microbes used to digest cellulose.

As previously indicated, termites are true social insects and have a very advanced social system with different forms (castes) carrying out different functions.  The castes in a mature termite colony are discussed below.

Reproductives-Queen/King. The sole function of the queen is to lay eggs. She is quite long-lived and, in some African species the queen may lay up to 10,000 eggs a day for 30 years.  She basically is a big egg laying machine with a huge abdomen and engorged ovaries. The queen termite is so large and heavy bodied that she is incapable of moving on her own. If there is a need to change her location, the workers will line up on one side and roll her like a pencil.  As the eggs exude from her abdomen, they are carried away by worker termites that also continuously feed her. There is a king which is diminutive when compared to the queen.  How he mates must be private as there is little in the literature about him. It must be difficult.

Queen of an African Termite is Capable of Laying 10,000 Eggs a Day for 30 Years. Image Courtesy entomart.

Supplementary or Substitute Reproductives. There are usually two types of this caste which are also known as neotenics. These may be either lightly pigmented with short wing pads (brachypterous) or very lightly pigmented with no wingpads (apterous).  As their names imply, they can lay eggs under certain conditions depending on species.

Replacement Reproductives of Subterranean Termites.  Image Courtesy of Jim Kalisch, Dept. Entomology, University of Nebraska.

Soldier Termites. Soldier termites are easily recognized by their relatively large heads and protruding mandibles. Soldiers functions to protect the colony against their chief enemies the ants. In the mound building termites of Africa, Asia and other tropical countries the world, soldiers instead of large  mandibles have funnel-shaped heads and can squirt a sticky substance for protection; these soldiers are called nasutes.

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Top. Soldier Subterranean Termite with Disproportionately Large Head and Jaws. Image Dr. Kaae. Middle Image.. Nasute Soldiers. Image Courtesy Felipe Fortez CC BY-SA 2.0. Right. Soldier Losing Battle Image Courtesy ETF89 CC BY-SA 4.0 

Worker Caste. The worker caste comprises the overwhelming majority of termites in a colony.  As their name implies, they perform all the work in a given colony.  This can include foraging for food (cellulose), care and feeding of the young and soldiers, excavating their tunnels or galleries and ministering to the queen.

An Army of Foraging Workers Guarded by Nasutes (clear heads) . Image Courtesy Bernard DUPONT CC BY-SA 4.0.

Alates. In the spring and or fall, depending on the species, a mature termite colony may form a large number of alate (winged) termites. These are the potential kings and queens of new colonies.  Very frequently, following the first seasonal rain, these alates will swarm, or fly, from the colony. The significance of swarming following the first rain of the season is several-fold. Termites are soft-bodied and susceptible to desiccation; therefore, moisture is conducive to survival.  It is also important that most of the colonies in an area swarm at the same time. This insures that mates will be found, and there will be cross mating between colonies to prevent inbreeding. Finally, the rain softens the soil (in the case of subterranean termites) and enhances the chances of some species forming new colonies below ground.

Hundreds of alates will leave a mature colony during swarming. They are weak fliers and many are lost to birds, ants and other predators. Because they are weak fliers, they do not fly great distances before settling down. Once a female alate leaves, she releases a sex pheromone from her abdomen that attracts an alate male. After mating, they both break off their wings that are no longer needed and burrow into the ground or into a wooden structure to start a new colony. Then they form a small cavity within which the female will lay several eggs. For the first year, the king and queen do not eat but dissolve their wing muscles to produce nutrients that they feed to the nymphs. Once these nymphs develop within the first year, they take on work duties. Colony growth is slow and there are no signs of this new colony in or around a structure for the first two to three years after initial infestation.

Swarming Termites after First Rain. Image Courtesy Ganesh Subramaniam Flickr  CC BY-SA 2.0.

The alates are the most likely caste someone is likely to see.  Therefore, it is to the advantage of the professional pest control operator to be able to distinguish and teach the differences in appearance of termite alates and carpenter.  Both are similarly appearing insects that can also swarm.  Even though they may seem similar, there are very distinct differences in the morphology of the two.

The order of termites is Isoptera.  Iso in Latin means equal and of course ptera refers to wings.  In winged termites, the first and second pair of wings is of equal size and shape, and in winged ants the second pair of wings is much smaller than the first.  Also with termites there are many more veins in the wings and when at rest the wings are held flat over the back.  In addition, the wings of termites are very large and extend way past the tip of the abdomen.  Ant wings only project slightly past the abdomen.  Ants have elbowed antennae and termites have bead-like antennae.  Finally, in ants the thorax is joined to the abdomen by a narrow stalk or petiole and that of termites is broadly joined.  I am sure that is more than you ever wanted to know about the morphology or structure of these two groups of insects.


Left. Carpenter (left) Ant with Elbowed Antennae, Petiole, and Unequal wings. Right. Alate Termite (right) with Beaded Antennae, Broad Waste and Equal Sized Wings that Lay Flat over the Back.  Images Courtesy of Jim Kalisch. University of Nebraska Entomology.


Drywood termites (Family-Kalotermitidae) establish their colonies in non-decayed wood with relatively little moisture content (generally 2.8 to 3 % water content).  Unlike subterranean termite, their colonies never require contact with the ground.  There are 16 species of Kalotermitidae in the U.S.  The most important in the West of are Cryptotermes brevis-the powderpost termite, Marginitermes hubarderi-the desert drywood termite and Incistermes minor-the western drywood termite.

Western Drywood Termite.  The western drywood termite is by far the most common and damaging of the three above mentioned species. The eggs of this species hatch in 30 to 60 days depending on temperature.  There are a total of 7 nymphal instars.  With drywood termites, there is no worker caste and the nymphs carry out the work duties.  The first three nymphal instars of drywood termites remain undetermined.  Once the 4th through the 7th instars are reached, they can eventually become either replacement reproductives, or soldiers, depending on colony need.  

The drywood termite can be identified in the alate form by its reddish head and thorax and light black wings. Mature colonies of drywood termites are relatively small and rarely number more than 5,000 individuals. Their colonies are almost always are found above ground, located inside wooden sections of the house or structure and more typically in attics and upper areas. Colonies of this species develop quite slowly.  A one-year old infestation typically contains 6 to 40 nymphs, one soldier and of course the king and queen. Three, four and 15-year old colonies will typically have 40 to 165 individuals with 3 soldiers, 70 to 700 individuals with 6 soldiers, and 2350 to 2750 individuals with 10 to 14 soldiers respectively. Alates typically are only produced after the fourth year. It is believed that the primary queen reaches her maximum egg laying capacity at about 10 to 12 years.  After that point, she declines quite rapidly and secondary or replacement queens will soon take her place.

As previously indicated, colonies of drywood termites tend to be relatively small when compared to those of subterranean termites.  Correspondingly, less rapid and sever damage may result from a colony of this type of termites when compared to those of subterranean termites.  However, proliferation of numerous colonies in a structure can result in severe damage.

Left. Alate Drywood Termite Captured by Crab Spider. Image Courtesy Bernard DUPONT from FRANCE

There are a number of signs or symptoms of the presence of drywood termites.  Of course, the homeowner is the likely to actually only see the swarming alates.  Swarming of this species typically occurs in the fall months (September, October) and more often than not on a sunny day with temperature around 80 F.  Of course, it is not uncommon for a number of these weak fliers to be caught in spider webs which can be a useful sign of an infestation.

The common indication of the presence of this termite is piled or scattered brown fecal pellets below infested wood.  Other than these fecal pellets, there is little evidence of their presence on the outside of the infested wood.  The pellets are kicked out of the termite galleries through small “kick holes” (about the size of a BB). The pellets typically are rectangular in shape with rounded ends and six flattened or depressed surfaces.  Longitudinal ridges occur at the angle between the six surfaces.

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Drywood Termite Fecal Pellets. Image Courtesy Sanjay Acharya-CC BY SA 2.0.

In addition, there frequently are many termite wings in an infested area.  Of course, these are due to the previous presence of alates which broke off their wings soon after mating.  It is quite easy to tell the type of termite that has been present by the galleries or tunnels inside the wood.  Drywood termites feeding galleries tend to cross the annual growth ring of wood while subterranean termites do not.


Cross Section of a 2 X 4 with Western Drywood Termite Galleries Crossing the Annual Growth Rings.  In Addition Galleries are Clean, Free of Soil. Image Dr. Kaae.

Drywood Termite Control.

There are several techniques that are used to treat infestations of the western drywood termite. These can be broadly categorized as whole structure treatment and local treatment.

The advantage of whole structure treatment is that it greatly increases the chances of total elimination of drywood termites from a structure.  If properly applied, fumigation and heat treatment will typically result in 100% control of drywoods and many other insect pests in the structure.  Of course, both of these treatments are considerably more expensive than any of the local treatments.  Also, neither of these gives any residual control.

Local treatments are less expensive than whole structure treatment and can vary considerably in effectiveness.  One limitation of these types of treatment is that even with great inspection techniques, it is quite possible that deep seated infestations cannot be found and therefore not treated. 

Microwaves.  Microwave generators are mounted against walls on a pole.  As with the common microwaves that are found in almost every home, these machines produce a penetrating heat which in this case is lethal to termites (basically the waves cook the termites inside the wood).  These machines typically are used for local infestations with each treatment limited to small areas.  As a result, the poles and microwave machines are moved to the next area after each treatment.

A disadvantage is that detection is critical to success and in some situations it is very difficult to locate deep seated infestations. In addition, microwave treatment may damage certain types of surfaces and other materials.  This is especially true with high voltage machines. The main advantage is that pesticides are not used. A factor that is attractive to some individuals.

Electricity.  High voltage electricity or electrocution is an additional nonchemical option for controlling drywood termites. In this case, infested damaged wood is exposed. Then an Electro-Gun is placed on one side and ground on the other side of the infested timber.  With use of electrical shock of low current (~0.5 amps), high voltage (90,000 volts), and high frequency (60,000 cycles), it passes through termite galleries and ultimately ends at the ground.   Death results from by electric shock or delayed mortality from the destruction of the termites' intestinal protozoa.

Besides the limitations of all localized treatments, the efficiency of this type of treatment may be reduced by interference of a number of standard building materials such as glass, concrete and metal.  In addition, if drill holes are required to reach infested, wood damage may occur to wall coverings and structural wood.

Freezing.  Liquid nitrogen is pumped into the infected area chilling it down to -20 degrees (F) and resultantly freezing the termites.  This is not practical for treatment of large areas, or near window glass (can shatter glass). Tarps are used for larger areas like porches.  Liquid nitrogen has no residual activity when used alone. Minor damage to the structure occurs from the holes drilled for spot liquid nitrogen insertion.

Drill and Treat with Chemicals. Wood injection or "drill-and-treat" applications have been used since the 1920s to treat drywood termite infestations which are accessible and detectable. An insecticide is injected into small holes drilled through any wood surface into termite galleries thus delivering the treatment directly to the pest population. This is the simplest and most direct method of treatment. The amount of drilling required and the effectiveness of this treatment depends on the chemical used and the nature of the infestation. Most chemicals will remain active in the wood after treatment to protect against resurgent colonies. This is the most effective of the local means of treating drywood termites.

Heat Treatment.  Heat treatment is a source of partial or complete building control for drywood termites.  In the case of complete control, nylon tarps are used to tent the building. Normally materials that are not heat resistant are removed from the building and water is left running to protect plastic pipes. With this technique propane heating units blow hot air in and around to heat the structure to120 F several hours to 130 F for a few hours.

 Whole structure heat treatment is attractive to certain homeowners who object to the use of chemicals. In addition, the process can be accomplished in a short period of time (hours) instead of days with fumigation.  Parts of structures (e.g.-apartments and condominiums) can be treated as opposed to fumigation where this cannot be accomplished. The major drawbacks of heat treatments include the difficulty in raising the internal core temperature of large structural beams that are infested and heat sinks.  These are areas within the structure that are difficult to heat, such as wood on concrete or tile.  In addition, materials such as plastics (e.g. electrical outlet covers), cable wiring and other sensitive material may be harmed by high temperatures.

Tent Fumigation.  Sulfuryl floride (Vikane) is the highly toxic, colorless, odorless gas that is used for fumigation.  Since it is odorless, a low percentage of chloropicrin (tear gas) is added to the main fumigant as a marker or indicator of the presence of the gas.  Fumigation (tent fumigation) with this material is highly effective when properly applied. An important aspect which increases the chances of successful fumigation is monitoring the distribution of the gas within the treated structure. This is accomplished by installing gas monitoring lines inside the structure undergoing treatment. Non-monitored fumigation may not have enough gas concentration to kill infestations and failures may occur.

Human deaths have been known to occur every year as a result of this practice. Vandals, thieves, and the homeless are the most common victims. A tented home with nobody home is a prime target for burglars. This procedure presents virtually no threat to the homeowner because Vikane has a very short residual and is gone within a short amount of time. Tear gas (choloropicrin) is mixed with Vikane as a warning agent and it will quickly alert the homeowner if any residual gas remains.  Tear gas has a longer residual activity than Vikane.


Home Covered for Tent Fumigation.  Image Courtesy of Lloyd Pest Control.

Fumigation has distinct advantages over localized treatment mainly in that it will typically eliminate infestations that are hidden from view. Major issues to consider with the use of fumigants include the difficulty of installing tarpaulins, the difficulty in determining the proper dosage, the need to protectively bag food items and the lack of residual control. In addition, the structure must be vacated for 2 to 3 days while it is being treated and then ventilated. Additionally, some types of roofs may be damaged by having tarpaulins dragged across them.  Of course there is always the reluctance of certain individuals to use pesticides in general. It should be noted even though sulfuryl floride is a highly toxic pesticide, that after the required three day treatment and ventilation period there is essentially no toxic residue of the chemical left. 

Termite Inspections. Anytime a house or other structure is sold and is financed by conventional means such as FHA, VA or banks, a termite inspection is required by the lending institution. The lender needs to be sure the structure is not totally riddled with these pests, as it legally owns the house until the loan is paid off (which in many cases take as long as 40 years). If a home is inspected and termites are found, they must be controlled before the loan is granted. Any termite damage or violations of the structural building code that may lead to termite infestation must also be corrected. In some cases the total cost of this work can be in the tens of thousands of dollars.

Subterranean Termites

Western Subterranean Termite-Reticulitermes hseperus.  This is the principle subterranean termite in the western U.S. ranging from British Columbia to Western Mexico and California to eastern Idaho and Nevada.  The alates are distinguished from other common species by their black to dark brownish coloration.   Swarming typically occurs in later-winter or spring although timing can vary considerable depending on area and weather.  As the name implies, colonies of these insects typically are found below ground. In some cases the colonies may extend as much as 30 feet below the soil surface. Mature colonies tend to be very large and can contain as many as 300,000 individuals. Soil moisture is a critical factor in the environment of these insects. Subterranean termites typically are more of a problem in clay compared to sandy soil.  Clay has more of a capacity to hold moisture over a longer period of time than doe’s sand.


Black Subterranean Termite Alate.

As with most termite colonies growth is slow.  Only a few eggs are deposited the first year and require an average of 50 days to hatch.  Even under the best of conditions, alates do not appear in a colony until the 3rd or 4th year.  The supplementary reproductive become quite prevalent and greatly accentuate growth of the colony.  However, since colony growth is slow, signs of a new infestation in a building will take 3 to 4 years.

Unlike drywood termites, subterranean termite colonies typically require ground contact.  Apparently if there is sufficient food, water and warmth colonies can survive above ground, but this is rare.  In most areas, the ground serves as a protective barrier against extreme temperatures and as a reservoir of moisture.  Unlike drywood termites, subterranean termites are quite susceptible to dry conditions.  Colonies of subterranean termites will readily change soil depth in order to seek favorable temperatures and moisture conditions.

Signs of an Infestation. In the U.S., if subterranean termites are found below a structure, they can gain access to the house by building earthen tubes (shelter tuber) or by working their way through inter-veining wood. They feed in the wood of the house but will also return periodically to the colony via the earthen tubes to replenish the moisture content of their bodies. If a house is built on a slab-type foundation, these termites can gain access to the home via cracks or holes in the slab for sewer inlets and gas fixtures.  The shelter tubes also serve to protect these termites from ant predators.   These shelter tubes are constructed out of sand or dirt, bits of wood and even fecal pellets.  These are bonded by a glue-like material that is secreted by the worker termites.

The western subterranean termite uses at least three types of shelter tubes.  Utility tubes are used to gain access to the house and run from the soil to the first wooden member of the structure and return to the soil to replenish the termites lost body moisture.  These tubes are typically flattened and wide in appearance.  Exploratory or migratory tubes are similar to utility tubes but typically do not extend to the wooden parts of the structure and are less sturdy and have small exit holes.  As their name implies, they are used to seek out new locations of food.  Suspend or drop tubes extend down from the wooden structure and may or may not reach the ground depending on their stages of construction.  They are normally lighter in color than the other types of shelter tubes since more wood fiber is used in their construction. They are used by stranded termites in attempt to return to the soil. Area Tubes1

 From Left to Right.  Utility, Exploratory and Drop Tubes. Images Courtesy Umberto Lopez.

Besides the earthen tubes, additional signs of an infestation of subterranean termite in a structure include the presence of  alates, wings that have broken off the swarming alates and the presence of dark areas in infested wood and blistering of the floor. Sometimes the distinct sound of soldiers can be heard by knocking or tapping infested wood.  When disturbed, this caste will violently jerk its head against the roof of the gallery and make a distinct almost ticking sound.  This is thought to serve as an alarm of possible danger to other soldiers. 

Subterranean termites feed primarily on soft spring growth.  As a result, the tunnels or galleries of these insect have more of a layered appearance as opposed to the random indiscriminant burrowing across and the grain of infested wood by the drywood termites.  In addition, these termites tend to bring small amounts of soil into their galleries and even pack chewed wood and other sources of cellulose into the unused portions of their galleries. Because colonies of these insects are so much larger than those of drywood termites, damage can be far more rapid with subterranean termites than with drywoods.

Wood with Subterranean Termite Gallery with Layered Tunnels Limited to Soft Spring Growth and Packed with Chewed Food.  Image Courtesy of University of Nebraska Entomology-Jim Kalisch.

Mound Building Termites-Termitidae

Mound building termites are found throughout the tropical areas of the world.  At maturity, a primary queen has a great capacity to lay eggs. The queen is widely believed to be a primary source of pheromones useful in colony integration, and these are thought to be spread through shared feeding (trophallaxsis).

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A Gigantic Queen Termite. Image Courtesy of Brutalux. CC BY-SDA 3.0

The king does not grow significantly after mating but amazingly (consider in the size of the queen) continues to mate with the queen for life. This is quite different from ant colonies where the queen mates once with the male(s) dying soon after mating, The queen in this case stores the sperm for life.

The worker castes carry out the various labors including brood and nest care, food storage, foraging, and in some species defense of the colony. As with other termites, the soldier cast primarily functions to protect the colonies against attack of ants and other potential predators.  Most species of Termitidae have unique soldiers (nasutes) that exude noxious liquids through either a horn-like head (nasus) or simple hole in the head (fontanelle).

termites, Nasutitermes spp.  (Isoptera: Termitidae)

Nasute Soldier Termites.  Image Courtsey Whitney Cranshaw.

In order to defend against the attack of ant or other predators, soldiers frequently block tunnels in order to prevent these insects from reaching the main areas of the colony.  This defense has significant built-in backups with soldiers standing behind soldiers so once the first line falls, others will take their place. In situations where an attack is coming from a gap that is larger than the individual soldier's head, defense requires numerous soldiers around the breach.  An additional self-sacrificing defense is performed by South-East Asian species referred to as the tar-baby termites.  In this case, the soldiers commit suicide by rupturing a large gland close to the surface of the exoskeleton.  As a result, a dense, sticky, yellow fluid is released entangling ants or other insects invading their colonies.

As previous indicated, termite workers build and maintain these giant colonies. These are massive, elaborate structures built from of combination of mud, soil, saliva, feces and macerated wood/cellulose.  These structures serve a variety of functions including providing a protected relatively safe location, and a source to collect water via condensation.  They consist of a maze of tunnel-like galleries that additionally serve as air conditioning and control the CO2/O2 balance.

Termite Mounds.  Images Courtesy Ouderkraal CC BY_SA 3.0

Colonies are typically constructed around or on top of large pieces of wood, inside fallen trees or on top of living trees. Large above ground mounds or termitaria are frequently constructed when an above-ground nest grows beyond its initially concealing surface. In Africa and Australia they are commonly falsely referred to as anthills.

 In tropical savannas of Africa, these termiteria can reach hug sizes of up to 30 feet high; however, 6 to 9 feet would be more common for the largest mounds in many savannas. The shape of these mounds vary from somewhat asymmetrical cones which are covered by grass and/or woody shrubs to well-sculptured hard earth mounds or a combination of both.  Typically species identification can be determined by the shape of these mounds. In some areas of African, a high density of these mounds dominates the landscaping. As an example, in the Busanga Plain area of Zambia, relatively smaller mounds of approximately 3 feet in diameter reach a density of approximately 300 per acre.  


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