National Formosan Subterranean Termite Program

Technical Info > Foraging

ABSTRACT

Fig. 1.—Typical area of C. formosanus infestation in Lake Charles, La. Note dead baldcypress trees that are infested with these termites.

Subterranean foraging galleries of a colony of C. formosanus Shiraki (Isoptera: Rhinotermitidae) were excavated in a filled, swampy area about 2 miles west of Lake Charles. Branches from 3 main galleries radiating from a dead baldcypress tree ramified over about 1.4 acres. These galleries were connected with food sources more than 200 feet from the original starting point. Species of trees attacked included dead baldcypress, dead pine, live wax myrtle, and live Chinese tallow. Live pine was not attacked by this termite. Most of the galleries were lined with carton material that varied in thickness and the galleries ranged from 2 to 46 inches deep. Vertical galleries branched from horizontal galleries and extended to the water table. A subterranean carton nest that contained 6 supplementary queens was found 19 inches below the soil surface and 25 feet from the nearest food source. Based on the date the swampy area was filled, it was apparent that this gallery system was less than 10 years old.

The Formosan subterranean termite, Coptotermes formosanus Shiraki, was first discovered at New Orleans and Lake Charles, La., in 1966. It was found infesting a warehouse in Houston, Tex., in 1965, but was believed to have been eradicated after the warehouse was fumigated with methyl bromide. It was found in Houston again in 1966, as well as in Galveston, Tex. In 1967 it was reported in Charleston, S.C.

Species of Coptotermes are widely distributed throughout the tropical and sub-tropical regions of the world. Lechleitner reported at the national Pest Control Association Convention in New Orleans in Oct. 1966 that species of this genus are considered the most economically important of all termites.

Several authors have reported on the gallery systems of various species of the genus Coptotermes. Ratcliffe and Greaves (1940) excavated galleries of C. lacteus (Froggatt) and found them ramifying from a central mound over about 1.5 acres and connecting with food sources up to 50 yd away. Gay (1946) traced a gallery of C. frenchi Hill from a nest in a dead tree to an infested house 70 ft away. Greaves (1959) traced a gallery of C. acinaciformis (Froggatt) which ran between 2 living trees. Erhorn (1934) reported on an infestation of C. formosanus at a sugar mill in Waipohu, Oahu, in which he found a foraging gallery 165 ft long and from 1 to 10 ft deep. Kalshoven (1941) reported that C. javanicus (Kemmer) often utilized roots as galleries.

Nests of C. formosanus have been found above and/or below the soil surface, in the base of living trees, in dead tree stumps, at the base of utility poles, and in other food sources in Louisiana. These nests consisted of soil and masticated wood that had been cemented together by saliva and excrement of the termites. This material is referred to as "carton" in the literature.

To obtain a better understanding of the subterranean foraging gallery system of C. formosanus, studies were initiated in Nov. 1966, on a site on the west bank of the Calcasieu River, about 2 miles NW of Lake Charles. The study areas was formerly a low-lying, water-covered swamp, populated by baldcypress trees, Taxodium distichum. Salt water intrusion after the excavation of a deep-water channel in the river and pollution from an adjoining industrial area beginning in 1930 were reported to be instrumental in killing the cypress trees (fig. 1). In 1956 the area was filled to a depth of 5-10 ft with soil pumped from the river bottom adjacent to the property. The top layer of fill consisted of a soft, dark gray clay, 0-18 in. deep. Below the clay layer a loose tan sand extended down to and below the water table. The level of the water table averaged about 31 in. throughout the excavated area during the period Nov. 1966 to May 1967. A reddish-brown transition zone, caused by oxidation, occurred between the clay and the sand. In 1956 a sand levee, about 40 in. high and 12 ft wide, was constructed parallel to the river. A drainage ditch opening into the river paralleled the southern boundary of the excavation site. The river on the east and the drainage ditch on the south were effective barriers to further gallery penetration in these directions.

Some pine, Pinus taeda; Chinese tallow saplings, Sapium sebiferum; wax myrtle bushes, Myrica cerifera; and broom sedge Andropogon virginicus, became established on the site after the fill work was completed in 1958.

Fig. 3.—Exposed flooring of C. formosanus gallery.

METHODS AND PROCEDURE

An encircling trench 18 in. wide and extending down to the water table was excavated 3-4 ft from the base of a dead baldcypress tree which was known to contain C. formosanus (Fig. 2) [Not shown]. Talc dyed with carmine red was then blown into each exposed gallery opening with a hand puff duster fitted with a tapered glass tube. Gallery openings were marked with stakes. Each gallery in turn was then traced outward from the trench. Branches from these various galleries were also marked with stakes for future excavation. With a shovel the soil was removed to within 1 in. above the gallery. A hand trowel was used to scrape the remaining soil from the top of the gallery and then a scalpel was inserted into the cartonous opening and the roof of the gallery was removed, leaving the floor exposed (Fig. 3). It was necessary to repeat this process for each foot of gallery exposed because of the constant horizontal and vertical turnings of the galleries.

The gallery positions were plotted on paper as they were being exposed in the soil. Locations of all curvatures and branches were fixed by compass and measuring tape. Gallery depths were measured at intervals as work progressed.

Fig. 4.—Subterranean foraging gallery system of c. formosanus. Lake Charles, LA., 1967. (Click image for full-size view.)

RESULTS

Gallery System.—The complete gallery system covered about 1.4 acres and is shown in Fig. 4. About 1900 ft of galleries were excavated. Enlarged drawings of those areas designated as A and B in Fig. 4 are shown in Fig. 5, 6 respectively [For Fig. 5, see Areas A; for Fig. 6, see Area B in Fig. 4]. However, a straight section of gallery 146 ft long shown in fig. 4 is not shown in fig. 5.

Five galleries were intercepted at the starting trench and of these 2 were small and could be traced only a few feet. The 3 remaining galleries were large and are designated as I, II, and III in Fig. 4, 5. Gallery I split into 6 branches about 3 ft from the trench. These branches extended to several food sources and 1 of them extended 108 ft SE of the starting point to a pine stump situated in the sand levee. The stump was trenched and galleries radiating from it were traced. Several of these galleries were traced to a subterranean carton nest 27 ft south of the stump. The nest was exposed and galleries radiating from it were located and traced (Fig. 7).

Gallery II was traced to a cypress log where it branched, the larger branches were traced to terminating points.

Gallery III was traced to several cypress stumps and logs about 130 ft north of the starting point. Galleries from these food sources extended northward for 55 ft through a sandy area, where they narrowed and branched into smaller galleries.

Description of Galleries.—The gallery system is depicted by lines of varying widths in Fig. 4, 5, and 6 to indicated the relative diameter of the gallery. The depth of galleries is indicated in Fig. 5 and 6 by Arabic numerals. Most galleries were lined with a reddish-brown carton material varying in thickness from a narrow strand of color to 1/4 in. The carton material was thicker in galleries running through sand where the clay surface layer was absent and it was of much darker color in these sandy areas. Galleries, excluding those in the sand levee, were constructed as horizontal slits not more than 1/8 in. high and ranging from 1/8 to 1 1/2 in. diam. Galleries in the sand levee were elliptical and ranged from 1/4 to 3/4 in. high.

The diameter of a gallery was apparently determined by its proximity to a food source or nesting site. Wide galleries that branched to various food sources were found radiating from the subterranean termite nest. Near major food sources galleries were found to merge and form a wider gallery. The width of galleries remained relatively constant between branch galleries—thus a widening of a gallery was indicative of a near branch gallery. Galleries 1/4-1/2 in. diam were found interconnecting main foraging galleries and running to food supplies containing little termite activity. Galleries 1/8 in. diam branched from larger galleries, food supply sites, and primary gallery termination points. These galleries were not lined and were very difficult to trace more than 5 or 6 ft.

When primary or large galleries terminated, many smaller galleries branched off in all directions and at varying depths. The southernmost gallery, which extended from the subterranean nest to a cypress log, branched into 4 smaller galleries in this manner. Gallery II also ended in several small galleries that ran immediately below the soil surface (surface galleries, Fig. 5). When galleries merged large triangular junctions were formed with a base of 5-11 in. and a median up to 9 in.

The depth of galleries ranged from 2 to 46 in. The shallowest galleries occurred in the area northwest of the starting point where the clay layer narrowed to less than 1 in. deep and finally disappeared as the galleries entered the sandy area (Fig. 4). Galleries running at depths greater than 20 in. were found only in the sand levee. The average depth of galleries in areas other than the sand levee was 9-10 in. In areas where a clay layer occurred the galleries were usually found in the transition area between the sand and clay. In areas where there was a deep clay layer the galleries penetrated the clay but followed the fissures in the clay rather than running a straight course. In 1 area the termites tunneled beneath a shale layer to a depth of 19 in.

Many galleries were found running through dead and living roots. In some cases galleries did not enter living roots but ran just beneath them. Roots containing termites are shown as broken lines in Fig. 6. These galleries were found primarily in the vicinity of the pine stump (Fig. 6). Frequently, where a gallery was found running through a root, another gallery would run directly beneath it and the two would be linked by numerous connecting shafts. Galleries in roots usually did not extend the entire length of the roots but branched at various distances. One gallery in a root from the pine stump was traced 27 ft to a point directly above the subterranean nest where the vertical shafts 1/4-1/2 in. diam led down to the nest. In some instances, when 1 gallery crossed over another, a vertical shaft connected the two. Other galleries from the pine stump to the nest ranged from 5 to 34 in. deep and were also connected with vertical shafts. However, in 1 instance where Gallery II crossed about 2 in. above a branch of Gallery III no vertical shaft connects were found.

At various points along the gallery systems, vertical shafts from 1/16 in. diam, had been constructed down into wet sand immediately above the water table. These shafts were most numerous in the sand levee and in Gallery II, just prior to its termination. The position of these shafts, represented by black dots, are shown in Fig. 5, 6. The shaft openings were encircled by a layer of carton material and were usually found at the edge of the gallery. In larger galleries, the openings of the vertical shafts were centered in the gallery floor but many of these shafts were filled with soil and appeared to be nonfunctional. Some smaller roots extending downward from lateral root galleries to the water table were found to be hollow and were presumed to be vertical shafts also.

Interwoven strands of cemented sand spaced every 1-2 in. were found extending, rafterlike, transversely across the concave roof of 1 gallery, that extended south from the subterranean nest. The gallery measured 1 1/2 in. wide and 1/4 in. high. The strands of cemented sand were found in the 1st 20 ft of the gallery and were not found in any other part of the gallery system.

Fig. 7.—Subterranean carton nest of C. formosanus.

Termite Nests.—An abandoned carton nest was found 41 ft from the ground in the baldcypress tree from which the excavations were started. the tree was 1 1/2 ft diam and 68 ft high. Carton material was found also encircling the base of the tree 1 ft below soil level. Carton material was found in several other locations in the gallery system but did no appear to be nesting areas.

The primary nest of the gallery system was found in the sand levee 135 ft southeast of the starting point (Fig. 7). The nest was situated 19 in. below the soil surface and consisted of a carton structure 21 in. wide by 19 in. high. The nest rested on a layer of cemented carton and sand. No wood was found near the nest except for some roots of a Chinese tallow sapling which had evidently grown through the nest after it had been constructed. No damage was apparent to either the roots or the tree.

The nest was encased within a cemented-sand covering which was about 1/4 in. in thick. The cemented-sand covering and carton material of the nest were flaked away with a scalpel. The outer 1-2 in. crumbled easily, but the carton was found to be harder as we progressed toward the center of the nest. The nest was in concentrically arranged cartonous layers. Small cavities were found throughout the nest, separated by thin cartonous walls.

Tree Species Attacked.—Wood from 4 species of trees, dead baldcypress, dead pine, live wax myrtle, and live Chinese tallow were found infested with C. formosanus. Although some pine saplings were growing in the same area, none was found infested with termites. Food sources are shown in solid black or in outline if heavily damaged (Fig. 4, 5, 6). Wood nearest the subterranean nest was the most heavily damaged. The logs had been reduced to shells and the wood was eaten away to a series of thin parallel sheets. The pine stump and its root system in the sand levee were severely damaged above the water table. No carton material was found in the stump. The cypress tree used as the starting point for excavations was only moderately damaged. The damage occurred in the core of the tree and extended up to the abandoned nest 41 ft above the ground. The cypress stumps 370 ft northwest of the nest also contained moderate damage in their cores.

The live wax myrtle plants received heavy damage in the roots, at the bases, and up into the trunks. The roots of the live Chinese tallow sapling were slightly damaged.

Activity Within the Gallery System.—Termite activity was found in the gallery throughout the period of escavations. Activity decreased on cold days when temperatures averaged about 4.4° C and on days when heavy rains occurred. Activity in shallow galleries was most affected by these changes.

Soldiers and workers were the only forms found in the galleries. When the galleries were first uncovered, soldiers were most conspicuous. However, as escavations progressed and galleries neared food sources, the subterranean termite nest, or terminating points, workers became more numerous. Many workers were uncovered when the trench around the subterranean nest was excavated. A positive correlation existed between the size of the gallery and the termite activity in it.

Six physogastric supplementary queens were found in the center of the subterranean carton nest. Five of these queens were situated together in a slitlike cavity 2 in. wide and 1/4 in. high. The 6th queen was situated in a similiar, adjacent cavity. All the queens were about 14 mm long. No primary king or queen was found in the nest. Several batches of eggs were found in cavities near the queens. Soldiers were the dominant form in the outer layers of the nest, but workers became more numerous toward the center of the nest. Various nymphal instars were found throughout the nest, but the younger nymphs were more numerous near the center.

A small group of workers and soldiers was found with a large number of brachypterous nymphs 15 ft above the ground in the cypress tree at the starting point of the escavations. A few soldiers were found in the carton material at the base of the tree.

The pine stump in the sand levee contained a large concentration of termites. Workers, soldiers, and many brachypterous nymphs were found in this location. Workers and soldiers were found also in other food sources associated with the gallery system, including the living trees.

Other Insects Associated with Gallery System.—Reticulitermes Flavipes Kollar was found throughout the excavated area. Its galleries consisted of small circular tunnels which ran through the clay layer. These tunnels were never found in the sand. The tunnels measured from 1/16 to 1/8 in. diam and usually were found several inches closer to the soil surface than were most of the galleries of C. formosanus. These galleries connected with wood lying close to the soil surface. At 1 point a series of 3x4-in. cavities, about 6 in. apart which contained nymphs of various instars was found connected by galleries in close association with C. formosanus galleries. However, the R. flavipes was never found in the same galleries with C. formosanus. On 1 occasion 2 small C. formosanus galleries were traced to within 1/8 in. of a R. flavipes gallery. On another occasion a C. formosanus gallery passed within 1/2 in. of a series of R. flavipes cavities. both species were found in a hollow root that extended southwest from the pine stump, but they were separated from each other by a section of the root that contained free water. C. formosanus termites were found in that portion of the root closest to the stump. The soldiers of R. flavipes were less numerous than those of C. formosanus, and they appeared to be less aggressive when disturbed.

Drywood termites, Incisitermes snyderi Light, were found in the outer 1—3 in. of the cypress tree where excavation was started. They were found also existing with C. formosanus in the cypress logs about 140 ft north of the starting point. However, there was no evidence that they were occupying the same gallery system.

Ants, Iridomyrmex pruinosus (Rogers); Collembola, Pseudosinella spp.; Zoraptera, Zorotypus hubbardi Caudel; and a fly Bradysia trifurca (Pettey), were also found in close association with C. formosanus.

C. formosanus Primary Nest.—A small nest containing a primary king and queen, workers, and soldiers was discovered 200 ft south of the starting point in a small piece of cypress wood. The queen measured 17.5 mm. long and 4.5 mm diam at the widest portion of the abdomen. Galleries from this nest were traced to small pieces of wood near the nest. Most galleries were small, the largest being 1/2 in. wide and 1/8 in. high. In 1 piece of wood situated 3 ft from that containing the king and queen, eggs and nymphs wre found in a small carton structure. All the galleries were traced to their terminating points and there appeared to be no connection with the main gallery system.

DISCUSSION

The age of the gallery system can be inferred by correlation with the fill data. The pumping of fill from the river continued from July 1956 until 1958. The fill used for construction of the sand levee was probably the 1st soil pumped from the river. Thus, the termite subterranean nest and galleries could have existed for openly about 10 years, or less. It is possible that primary reproductives infested a food source above the water level and once the fill was placed in the area, galleries could then have been extended into the soil. Although it was impossible to determine the conditions under which the supplementary queens were produced, the subterranean nest is believed to have been the central nesting area of this gallery system. The largest concentration of galleries radiated from this nest and all the food supplies found within 100 ft of the nest had received heavy damage. It seems plausible to assume that as food supplies nearest the nest were consumed, the termites extended their galleries to new food sources.

The vertical shafts branching from horizontal galleries probably were used to maintain a constant high humidity in the gallery system. Ratcliffe and Greaves (1940) reported shafts of this description in galleries of C. Lacteus. Greaves (1962) also reported finding shafts associated with C. acinaciformis and C. bruneus Gay. However, none of these species was reported to construct as many shafts as were found in the gallery system excavated in our study.

The largest concentrations of shafts wre foundd in areas consisting primarily of sand which lacked a clay covering. This circumstance was especially true of the more shallow galleries. Since loose, porous sand has a high surface evaporation rate, the shafts probably served to constantly infuse moisture into the horizontal galleries. In areas where a clay covering was present, there were fewer vertical shafts. In these areas, the clay apparently served as a "lid," slowing the surface evaporation rate.

Greaves (1962) reported that galleries of C. brunneus in sand were constructed as slits in tubes of cemented sand. He surmized that by cementing the sand around each gallery the termites might aid in preserving a high humidity within the galleries. The thick cartonous lining around the C. formosanus galleries running through loose sand also probably served this same function. In addition, the thick lining and elliptical shape of the galleries probably added strength to the gallery structure.

The gallery depth varied with the thickness of the clay cover. Where no clay layer was present, the galleries ran deep. Galleries were seldom constructed in clay. In forming galleries in soil, termites do not remove the soil to a great extent but compress it away from a central starting point, forming a compact layer around each gallery (Greaves and Florence 1966). Ebeling and Pence (1957) reported that in moist sand termites excavate by pushing their heads forward, then pressing the sand particles to either side. The smaller particles are taken into the buccal cavity and placed along the walls of the tunnel to form a smooth and titly sealed surface. The fact that termites do not necessarily remove the soil in gallery construction but compress it to the side by pushing their heads forward could, in part, explain why C. formosanus rarely extended its galleries into the clay. However, galleries of R. flavipes were found running not in the sand but through the clay.

Depth, size, and shape of C. formosanus galleries, as well as the number of vertical shafts extending to the water table, probably depend on edaphic factors such as soil moisture, soil gases, and soil temperature.

We believe that the small, unlined galleries branching from the larger galleries, were for explorations. Indications are that the entire gallery area was explored by subterranean tunneling. Several times during gallery excavation, traces of smaller galleries were found running through larger operative galleries. Probably when contact had been made with a new food supply a larger gallery was directed through the smaller gallery. A succession of consumed food supplies encircled the subterranean termite nest. From these food sources radiated other galleries, including numerous exploratory galleries. This fact indicates that C. Formosanus expand their gallery system by moving from 1 food supply to another; first by means of smaller galleries to locate food supplies then enlarging them to accomodate increased activity. Ratcliffe and Greaves (1940) and Gay (1946) have suggested the possibility that surface scouting plays some part in the discovery of food by C. lacteus and C. frenchi.

The most conspicuous form in the galleries when they were first uncovered was the soldier caste, probably because of the defensive function of this caste. Large numbers of workers were later found as galleries terminated, neared food sources, or the subterranean nest. It is postulated that the workers were probably retreating as gallery excavation advanced.

ACKNOWLEDGMENTS

We thank R.J. Gagne and A.B. Gurney, Entomology Research Division, USDA, Washington, D.C., and M. Kyle, Entomology Department, Louisiana State University for determining insect species; J. H. Roberts, Entomology Department, Louisiana State University and Stanley McKenzie, McKenzie Pest Control, Lake Charles, LA., for photography: and William Iglinsky, Biology Department, McNeese State College for his assistance during this investigation in Lake Charles.

REFERENCES CITED

Ebeling, W., and R. J. Pence. 1957. Relation of particle size to the penetration of subterranean termites through barries of sand or cinders. J. Econ. Entomol. 50: 690-2.
Ehrhorn, E. M. 1934. The termites of Hawaii, their economic significance and control and the distribution of termites by commerce, p. 321-33. In Kofoid et al. [ed.] Termites and Termite Control. 2nd ed. University of California Press, Berkely. 1946. A case of house infestation by a tree dwelling colony of Coptotermes frenchi Hill. J. Counc. Sci. Ind. Res. Aust. 19: 330-4.Greaves, T. 1959. Termites as forest pests. Aust. Forest. 23: 114-20.
1962. Studies of foraging galleries and the invasion of living trees by Coptotermes acinaciformis and C. brunneus (Isoptera). Aust. J. Zool. 10: 630-51.Greaves, T., and R. C. Florence. 1966. Incidence of termites in black-butt regrowth. Aust. Forest. 30:153-61.
Kalshoven, L. G. E. 1941. Groundplans of termite nests. Entomol. Med. Ned.-Indie. 7:30-34.
Ratcliffe, F. N. and T. Greaves. 1940. The subterranean foraging galleries of Coptotermes lacteus (Froggatt). J. Counc. Sci. Ind. Res. Aust. 13: 150-61.

Reprinted from the
ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA
Volume 62, Number 3, pp. 536-542,

¹ Isoptera: Rhinotermitidae [Return to top]
² A portion of a thesis by the senior author to be submitted to the Graduate Faculty of Louisiana State University, Baton Rouge, in partial fulfillment of the requirements of the degree of Master of Science in Entomology. This study was supported in part under a study plan FS-50- 2201-0.504 with the Wood Products Insect Laboratory, Southern Forest Experiment Station, United States Forest Service, Gulfport, Miss. Accepted for publication June 3, 1968. [Return to top]
³ Research Assistant and Professor of Entomology, respectively, Entomology Department, Louisiana State University, Baton Rouge. [Return to top]