FormosanSubterranean Termites

L-523311-01

Roger E. Gold, Harry N. Howell, Jr. and Grady J. Glenn*

Formosan subterranean termites are wood-destroying insects native to Central Americaand the Far East that have been introduced

into the United States. They are considered themost aggressive and economically devastating ter-mites in the country. Like other subterranean ter-mites, Formosan termites feed on materials thatcontain cellulose, but they attack a greater varietyof materials at a faster rate than native termites.They have an enormous reproductive capacity,and a typical colony will exceed 1 million insects.

Although considered “subterranean” (under-ground, hidden) in habit, the members of thegenus Coptotermes regularly construct aerial(above ground) nests within the structures theyinfest. This possibility of both a subterranean nestclose to the infested structure and an aerial nestwithin the infested structure can greatly increasethe damage potential of these termites.

DistributionThe first infestations of Formosan termites in

the state were collected in 1956 from a floatingdry dock on the Houston Ship Channel in the cityof Pasadena, Harris County, Texas. Since then,Formosan termites have been detected in 15 coun-ties in Texas: Angelina, Aransas, Bexar, Dallas,Denton, Galveston, Harris, Hidalgo, Jefferson,Liberty, Nueces, Orange, Smith, Tarrant, andTravis (Fig. 1).

It is believed that Formosan termites weretransported to the Houston Ship Channel in wood-en cargo from the Far East. In many cargo holds,

large timbers (shores) are used to hold crates andcontainers to prevent their shifting during passage.At the port of destination, these timbers areunloaded from ships so the cargo can be removed.

These shoring timbers have been thought to bea primary source of introduction of the Formosantermite into the port cities of Texas and possiblyother parts of Texas. Shoring timbers are used notonly for their original purpose but often are takenfrom the docks and used by landscaping compa-nies for construction of terraces or planting beds.If these infested timbers are not properly fumigat-ed with an approved fumigant, the termites cantravel with the timbers and infest the soil at alandscaping site. And while most of the infesta-tions in inland cities in Texas likely occurred inthis way, in Angelina County and Smith County in

*Professor and Extension Specialist in Urban Entomology, AssistantExtension Entomologist, and Research Associate; The Texas A&MUniversity System.

Figure 1. Known distribution of the Formosan termite in Texas.

east Texas, the termites probably arrived in pinemulch used in horticultural operations. Sod frominfested areas and cargo pallets that have restedon infested soil have also spread the Formosantermite into Texas.

An initial infestation in a city can become aseed colony for subsequent infestations in thatneighborhood or in distant locations. For example,in 1994 a neighborhood in the northern part ofAustin, Texas, discovered an infestation of theFormosan termites. Within six years, 10 moreinfestations were discovered in the neighborhood.An additional infestation was discovered three-fourths mile north of that neighborhood in 1999.

IdentificationFormosan termites are social insects. Three

forms, called castes, are found in the colony—reproductives (winged or wingless), soldiers andworkers (pseudergates). Soldiers and wingedreproductives (alates) are the castes used for iden-tification purposes. Figure 2 shows the life cycleof the termite.

Winged reproductives (swarmers): WingedFormosan termite reproductives or “swarmers” areyellowish-brown in color and 12 to 15 mm long

(0.5 to 0.6 inch) (Fig. 3). They swarm at night andare attracted to lights. They have a dense coveringof hair on their wings, as do other species of ter-mites native to Texas. (Some drywood termites arealso a honey-brown color and are about the samesize as Formosan termites. They, too, swarm atnight and are attracted to artificial lights.) The twospecies can, however, be distinguished by otheridentifying features, such as veins in the wingsand characteristics of the head (Fig. 4). If indoubt, have the termites identified by theDepartment of Entomology at Texas A&MUniversity (979) 458-0852 or (979) 458-0853.

Samples for identification may be mailed toCenter for Urban and Structural Entomology,Department of Entomology, MS 2475, Texas A&MUniversity, College Station, TX 77843-2475.

2Figure 2. Life cycle.

Figure 3. Swarmer.

Figure 4. How ot distinguish Formosan and Drywood termits.

Forewing of Drywood termite

Three or moreveins at frontmargin

Forewing of Formosan termite

Two veins atfront margin

Head of Drywood Swarmer

Clypeus notdivided

No fontanelle

Head of Formosan Swarmer

Dividedclypeus

Fontanelle

Workers: Workers of Formosan termites arewhite to off-white in color and are difficult to dis-tinguish from other termite species (Fig. 6). Al-though ants often swarm at the same time of yearas termites, it is easy to distinguish ants from ter-mites by body, wing, and antenna shape (Fig. 7).

Biology and habitsFormosan subterranean termites belong to the

same family as native subterranean termites (fam-ily Rhinotermitidae). They construct their primarynests in the soil of a material called “carton” (Fig.8). When they infest a human-made structure,they can form this carton in the wall spaces (Fig.9). Formosan termites often live for months oreven years on the moisture in the carton materialwhile they feed on wood in the above-ground por-tions of a structure. If the colony is separatedfrom its subterranean nest, this aerial nest canstill survive, and the termites can continue todamage the structure.

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Figure 8. Carton nest.

Soldiers: Formosan termite soldiers have tear-dropped or egg-shaped heads compared to themore parallel-sided head of native subterraneantermites (Fig. 5). Formosan termite soldiers aremore aggressive than native subterranean termitesoldiers and, when disturbed, exude a smallamount of a white, defensive secretion from thefontanelle, a gland located on the front of thehead.

Figure 5. Soldiers.

Figure 6. Workers

Figure 7. Distingush ants from termites.

When new nests and foraging areas are estab-lished, the colony can expand rapidly. Like othertermites, Formosan termites feed on cellulose,including living plants. They have been known toattack more than 47 plant species, including cit-rus, wild cherry, cherry laurel, sweet gum, pecan,cedar, willow, wax myrtle, Chinese elm and whiteoak (Fig. 10). While native subterranean termitesgenerally feed on the softer wood produced dur-ing spring growth and avoid the harder summergrowth wood, Formosan termites eat both (Fig.11). The damage resembles that of drywood ter-mites but lacks the fecal pellets in the feeding gal-leries. Like other subterranean termites, they mayalso chew through non-cellulose material, such asasphalt, plaster, creosote, rubber, and plastic,searching for food and moisture.

Signs of infestationThe presence of swarmers, shed wings or dam-

aged wood signals that termites are infesting astructure.

Swarmers: The first sign of an infestation gen-erally noticed by homeowners is the presence ofswarming reproductives on window sills or nearindoor lights. Because Formosan termites swarmat night and are attracted to lights, a homeownermay first notice the swarmers around porch lightsor during a night-time backyard party. The pres-ence of swarmers warns that termites are nearand possibly attacking a nearby building.Swarmers inside a house almost always indicatean active infestation in the structure.

Shelter tubes: Shelter tubes constructed of soiland ascending from the soil up the side of a foun-dation are sure indications of a subterranean ter-mite infestation (Fig. 12). When broken open, theactive tubes will be filled with termite workersand soldiers.

Figure 9. Carton in wall.

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Figure 10. Damage to tree.

Figure 11. Damage in wood.

Figure 12. Shelter tube.

Damaged wood: Wood damage often is notdiscovered initially but definitely indicates thepast or present presence of termites. Frequently,damaged wood may be hidden under a coat ofpaint; this wood will yield a dull sound whentapped with a hard object. Wood damaged byFormosan termites resembles wood damaged byother subterranean termites in that it will containdeposits of soil.

Nests: Formosan termites often make aerialnests of chewed wood, soil, saliva, and fecal mate-rial. These nests can be as large as several cubicfeet and can be found both in the soil and aboveground level in buildings.

ManagementControl measures include reducing the potential

for subterranean termite infestation, preventingtermite entry, and applying residual chemicals forremedial treatment.

Inspection Thorough inspections can determine whether

infestations and damage are present, whetherremedial control measures are needed, and dis-cover any conditions that can encourage termiteattack. Inspections can be performed by anyonewho knows the basic construction elements, theenvironmental requirements for termite survivaland the behavior of subterranean termites.

Tools and equipment needed for an inspectioninclude a flashlight, ice pick or sharp-pointedscrewdriver, ladder and protective clothing (bumpcap, coverall, rubber knee pads). A clipboard,graph paper and floor plan or sketch help recordinspection findings and ensure that the entirestructure has been examined. A moisture metercan often detect increased moisture levels in theshelter tubes hidden behind walls as well as highmoisture conditions that encourage Formosan ter-mite infestations.

Where to check outside. Examine the founda-tion of the house, garage and other structures forshelter tubes coming from the soil (Fig. 12). Payparticular attention to attached porches, connect-ing patios, sidewalks, areas near kitchens or bath-rooms and narrowly confined or hard-to-seeplaces. Check the soil moisture around or underthe foundation to determine if faulty grade con-struction creates moist areas next to the structure.Check for termite infestation or wood decayaround window and door frames and where utili-

ties (air conditioning pipes, gas and electric ser-vices) enter the structure.

Observe roof eaves and gutters for defects thatmight cause leaks and eventual wood rot. Inspectbehind closely planted, dense shrubbery orfoliage. Note particularly any earth-to-wood con-tact such as fences, stair carriages or trellises.

Where to check inside. Check the inside wallsfor shelter tubes (Fig. 13). A moisture meter isextremely helpful in locating nests hidden in wallspaces and ceilings. Probe or sound exteriorporches, doors and window facings, baseboards,and hardwood flooring, being careful not todeface finished wood when probing. Examine anyattached earth-filled porches, known or suspectedjoints, cracks or expansion joints in the foundationand unusual blistering in paint or wallboard sur-faces. Discoloration or staining on walls or ceil-ings may indicate water leaks that can decaywood and aid termite infestation. Especiallyinspect where plumbing or utility pipes enter thefoundation or flooring.

Check the floor covering for raised or splitareas. Examine the plumbing, particularly in bath-rooms on slab construction. There should beaccess to the bath trap area. If none exists, build aremovable plumbing hatch for periodic inspec-tion. Examine the attic for shelter tubes, waterleakage, wood rot or damaged wood. If the houseis of pier and beam construction, inspect the areabetween the floor and the underlying soil (crawlspace). Crawl space should have a minimum of 18inches between floor joists and the underlying soiland at least 12 inches between floor beams andthe soil.

Examine the inside of beams, chimney bases,hearths or piers for shelter tubes. Look at areasunderneath or close to earth-filled porches, patios,

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Figure 13. Shelter tubes on interior walls.

planters and bathrooms for water leakage and ter-mite damage. Remedial action may be required tocontrol moisture if water stands underneath thehouse. Observe the top of the foundation wallwhere the floor and the wall intersect. Closelyinspect plumbing and utility lines passing throughthe floor of foundation walls.

Preventive managementPrevention is the best management tool against

Formosan termites. The best time to protectagainst any termite species is before and duringconstruction. At that time, treat the soil under andaround the foundation with the recommendedinsecticides.

After the foundation is completed, remove allwooden form boards and reinforcing stakes.During construction, avoid placing any siding orinsulation material in contact with the soil orbelow grade. There should always be a 4- to 6-inch gap on the foundation between the soil gradeand lower edge of any siding material to permitthorough regular inspections for termite activity.Pressure treated lumber containing ACZA, CCA orDOT will prevent termite infestation. Ask yourbuilder about these materials.

Remedial treatmentSeveral options are available for the remedial

treatment of Formosan termite infestations: barri-er treatments, tent fumigation, and baiting pro-grams. The methods may be used alone or incombination.

Barrier treatments. The purpose of this typeof control measure is to establish a barrier oftreated soil around a foundation’s perimeter andat the point of any penetrations through slab foun-dations. Spot treatments may not stop Formosantermites from gaining access elsewhere in thestructure. Even a thorough treatment around theperimeter of the foundation and all plumbing pen-etrations may not be successful if the termites canenter a structure through hidden cracks in thefoundation. Find and treat all possible entrypoints that termites might use.

Formosan termite colonies are large and persis-tent about gaining access. Also, structures shouldbe thoroughly inspected to discover and eliminatemoisture sources that termites could use to buildaerial nests. The aerial nests, or carton, should belocated and removed. Again, a moisture meter is avaluable tool in locating aerial nests.

Fumigation. Fumigation is the use of a poisongas to penetrate the wooden parts of a structure.Professional pest control operators have thechoice of two fumigants registered for the controlof Formosan termites: Brom-O-Gas® (methyl bro-mide) and Vikane® (sulfuryl fluoride). When fumi-gation is completed and the structure is vented,no residual pesticide remains for future termitecontrol or prevention. The use of fumigationalone, with no soil treatment, does not prevent re-entry of termites from the soil.

When fumigation is used, three steps must beperformed, in this order, to control Formosan ter-mites:

1. Establish a chemical barrier in the soilaround the foundation of the infested struc-ture and at all entry points such as plumbingpenetrations and cracks in the foundation.

2. Remove all carton nest material.

3. Conduct a tent fumigation.

Baits. These products should be called “feedthrough termiticides” rather than baits. The termbait generally is reserved for substances that willattract insects. The termiticide baits presentlyavailable do not attract termites; the substancesare merely palatable to them. These termite baitscontain chemicals that will kill the members ofthe termite colony, similar to the use of baits tocontrol fire ants. Foraging termites feed on thebait and return to the nest to share it with theother termites in the colony.

There are several choices in baiting systems.Above-ground baits are placed in contact withlocations where the termites are actively feedingon wood. Within a few days, the termites willbegin to feed on the bait and transfer it through-out the colony. Baits are also placed in the soilsurrounding the structure. These bait stations pro-vide an additional source of bait; however, thetime required for the termites to begin to feed onthe in-ground baits is several months longer thanrequired for the termites to begin to feed on theabove-ground baits.

Use of such a baiting system requires a pestcontrol operator knowledgeable about termitebiology and behavior to apply the baits correctlyand monitor the process aggressively. Bait systemsare an active form of termite control requiring fre-quent visits by the pest control operator in chargeof the job.

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Due to the higher rate of consumption byFormosan termites, baits must be inspected on abi-weekly basis rather than on a monthly interval,as with native subterranean termites. The baitsstations should always contain fresh bait. Afterseveral months, the interval between bait inspec-tion and replacement can usually be extended tofour weeks as the number of remaining termitesdeclines.

Some baiting systems are used in combinationwith liquid termiticide applications. Other baitingsystems have been designed for use without otherchemicals. In general, baits require several trips toa site for installation and monitoring. Control maytake from a few weeks to more than one year.

Treatment of infested treesA tree infested by Formosan termites also

requires treatment to eliminate the infestation andto prevent further damage to the tree or even thedeath of the tree. Termites in infested trees canspread to other structures. Applying termiticide tothe surface of the bark will not control Formosantermites, which hollow out the center of a treeand construct their carton nests in the void (Fig.10).

To manage a Formosan termite infestation in aliving tree, drill into the tree above the soil lineand locate the void area. This may require severalexploratory drill holes before the space is located.

Then inject an approved termiticide into the void.Foaming termiticide is a valuable tool in thesetreatments—the foam expands within the voidspaces in the tree, allowing a more thorough appli-cation of the chemicals.

Keys to managementFormosan subterranean termites pose signifi-

cant potential for structural damage and expense.It is important, therefore, that a homeowner usethe proper techniques to manage these termites,including:

� Accurate, positive identification of the sol-diers or winged reproductives.

� Thorough knowledge of their biology andbehavior.

� A comprehensive inspection based on thatknowledge.

� A thorough, aggressive treatment program.

� Meticulous annual inspections to detect evi-dence of termite activity.

� Preventive management measures, such asmaintaining a gap between soil grade andbuilding materials.

For further information seehttp://termites.tamu.edu.

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The information given herein is for educational purposes only. Reference to commercial products or trade names is made withthe understanding that no discrimination is intended and no endorsement by Texas Cooperative Extension is implied.

Produced by Agricultural Communications, The Texas A&M University SystemExtension publications can be found on the Web at: http://texaserc.tamu.edu

Educational programs of Texas Cooperative Extension are open to all people without regard to race, color, sex, disability, religion, age or national origin.Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, andJune 30, 1914, in cooperation with the United States Department of Agriculture. Chester P. Fehlis, Deputy Director, Texas Cooperative Extension,The Texas A&M University System.10M, Revision