1. Wood-boring insects may be grouped conveniently into those which damage: 1) standing trees or newly felled
logs; 2) sawn timber and wood products during seasoning or storage; and 3) wood in use. They may also be
further grouped as to whether they attack hardwoods or softwoods or attack heartwood or sapwood. Certain
insect species attack more than one of these groups.
Three things are necessary for insect attack - a source from which the infestation spreads, susceptible wood,
and suitable conditions of temperature and humidity. Relatively little is known about some factors which make
certain woods more attractive to insects than others, but insects are often quite selective. Fungal decay in wood
often renders it more susceptible to infestation, but may also repel insects. Some insects may tolerate wide
ranges of physical conditions; others cannot survive great fluctuations in temperature or humidity. Prevention of
attack by insects is sometimes closely related to the proper handling of lumber during milling and storage,
Signs of damage. Insect attack is generally characterized by tunnels or cavities (often containing wood powder
or fecal pellets) within the wood. In many cases there are holes of various shapes and sizes on the surface. The
wood powder (frass) may be pushed out through the holes, forming small piles beneath or on the surface of
infested wood, indicating that adults have emerged recently or that live insects are working inside the wood.
Sometimes, when attack is severe, the wood may be reduced to a hollow shell or to a powdery condition. In
other cases, there may be very little external evidence of attack, and the interior condition of the wood can only
be determined by probing with a sharp instrument or by striking or pounding the surface (sounding) to detect
hollows by sound differences.
No part of the United States is completely free from wood-destroying insects. The problem in Alaska is so small
as not to warrant concern. The problems in tropical and semi-tropical areas are at the opposite end of the
spectrum.
Potential economic losses and significance of the damage inflicted, as well as appropriate control measures,
depend upon the type of pest involved. It is therefore essential to accurately identify the cause of the damage
and to distinguish insect damage from other factors involved in the deterioration of wood. Failure to appreciate
these points often results in unnecessary treatments.
2. The subterranean termite, (see example), the drywood termite, (see example), and the dampwood termite, (see
example) are the three types of termites common in California. Different types are more prevalent in different
areas. Example, i.e., dampwood termites in northern coastal area, drywood termites in southern California. Pest
control operators must have knowledge of all types and should be aware that rare infestations of other types of
termites can occur in their area.
Subterranean termites are the smallest in size but the most destructive and numerous. Drywoods are mid sized
and probably the most costly to control. Dampwoods are the largest and probably the easiest to control.
Termites have incomplete metamorphosis. They hatch from eggs as “nymphs” and need the adults to attend to
the eggs. They go through seven instar molts. Some then change to soldiers or swarmers “alates”. There is no
worker class in the drywood or dampwood termites. All of the nymphs become soldiers or swarmers and the
nymphs do the work of the workers in the colony.
All termites convert cellulose to starch by protozoa in the gut. They must get protozoa from other members of
the colony. When the colony gets larger, the food supply is short, or conditions change, swarming occurs. This
swarming usually occurs in the spring or fall for subs and dampwoods after a rain or on a bright clear day.
Drywood termites normally swarm mid day in the fall, Sept. to Nov. Termite swarmers are poor fliers and usually
travel a very short distance. On landing, they shed their wings, mate and start a new colony.
Termite workers are cream colored with no wings and no mandibles. Subterranean termite swarmers are black.
Drywood termites and dampwood termites are reddish brown and either have wings or wing pads. Dampwood
termite wings are much longer than the body of the termite. Soldiers can be identified by the big head and
mandibles. Drywood termites can exist in wood with a moisture content as low as 3%.
The genus of drywood termites were recently split off. The western termite formally called kalotermes are now
called incisitermes minor hagen. Termites work around the clock. Subterranean termite workers live from 3 to 5
years. Queens and supplemental reproductives live longer.
3. TERMITE BIOLOGY
Several reasons that termites are destructive:
1. The individuals are long lived.
2. The colony is self-perpetuating.
3. They have a constant source of food.
4. They are social insects and thus cooperate.
5.They are protected from extremes of heat and cold and from their enemies by their cryptobiotic mode of life:
all of which results in constant increase in destructive powers. A termite is an insect with three body segments,
head, thorax and abdomen; four equalized wings, with six legs attached to the thorax and with a pair of beaded
antennae. Of the major constituents of wood, cellulose is readily digested by the enzymes of protozoa living in
the digestive tracts of termites, whereas lignin is entirely indigestible, so that wood with high lignin contents is
invariable avoided. Sapwood is more attractive than heartwood. The lower intestine of the termite contains a
swarming mass of one celled protozoa. These minute protozoa contain enzymes which digest the wood
fragments. If their protozoa are removed, the termites die of starvation. The highly specialized king, queen,
soldiers and the first instars depend upon nymphs and workers for their feeding. If these dependent individuals
are isolated, they starve since they are unable to feed themselves.
Termites aid in the dissemination of fungi by providing shelter and humid atmosphere necessary to fungi growth.
Fungi renders certain services to the termites:
1. The fungus provides moisture for the termite when consumed.
2. Fungi may be of some value to termites in the preliminary softening of wood.
3. Fungi provide a supply of protein and vitamins for the termite.
Termites clean themselves by licking or grooming one another. This results in each termite consuming the
secretions of the other. While the grooming is going on, the termites exchange nourishment by mouth. This
exchange of nourishment is known as trophallaxis.
Termites have a caste system in their colonies. Subterranean termites have reproductives, workers and soldiers
and swarmers whereas dampwood and drywood termites lack a true worker caste, their immature nymphs do
the work of the colony. The reproductive caste consists of male and female. The male termite mates throughout
his life with the queen. These reproductives swarm at certain times of the year. Subterranean termites swarm
both in the spring and the fall whereas the main swarming of drywoods occurs in the fall. Swarming usually
occurs just after a rain when the sun shines brightly.
4. The average soldier or worker lives only two or three years but queens may live much longer.
There may be several supplementary queens in each colony. These supplementary queens readily replace the
primary queens when the latter die or are injured. The supplementary reproductives are important because they
rapidly increase the termite population. Termites as a rule avoid light and seek narrow cracks and crevices. The
winged reproductives may wait three months or more for correct atmospheric conditions before swarming,
especially as far as temperature and humidity are concerned. The alates or winged reproductives then
completely reverse their instincts and seek light and open spaces. The flight is short and weak. The termite
wings break off at a fracture point, the termites pair off, mate, and form a new colony.
The worker is the form which does all of the work of the colony such as constructing tunnels, excavating
chambers, cultivating fungus gardens, obtaining food, feeding the young, the soldiers, and the king and queen.
The sole purpose of the soldier termite is that of defense of the colony particularly against their arch enemy, the
ant.
Termites are world wide in distribution but are absent from the arctic and antarctic areas. Some 1,800 species of
termites have been identified. There are approximately 45 species in the United States.
Termites have broad waists and bead-like antennae. Ants have narrow, pinched waists and elbowed antennae.
5. THE WESTERN SUBTERRANEAN TERMITE
(RETICULITERMES HESPERUS)
The subterranean termites are ground dwelling termites which nest in the soil, or in the wood or vegetable
material in contact with the ground. They are able to reach wood or cellulose material above the ground level by
means of earthen tubes which they build. Since these termites are dependent on soil moisture, they must
usually have a ground connection. There are rare exceptions where they have been able to maintain
themselves in damp wood with moisture at or greater than 14% even after the ground connection was broken.
Unlike drywood and dampwood termites, their feces consist of liquid drops, not pellets, which characteristically
spot their excavations in wood. In their galleries frass is also characteristic. The frass consists of masticated
wood and earth cemented together with saliva and liquid feces to form a mud-like cement.
The sexually mature reproductives, known commonly as swarmers, bunch up inside to the nest near the exit
hole. When the right combination of moisture, temperature, and light intensity is present, they swarm out of the
colony and fly away to form a new colony. Swarmers are not given off from a western subterranean termite
colony until after the colony is at least 2 to 3 years old.
After the male and female reproductives (Alates) have swarmed from a colony, they pair off and attempt to
establish a colony of their own. The successful pairs manage to excavate a cell. They seal the exit with bits of
debris cemented together with the liquid fecal material. Copulation takes place only after this cell is prepared
and sealed closed. The male (king) cohabits with the female (queen) throughout the life of the colony.
When a subterranean termite is hatched from the egg, it is called the First Instar Nymph. When it molts (sheds
its exoskeleton) for the first time, it becomes a second instar nymph. If the individual is destined to become a
reproductive (alate), it will shed its skeleton six separate times to finally become a seventh instar stage which is
the fully developed reproductive stage (swarmer or alate). After the fourth instar stage has been reached, those
nymphs that are destined to become reproductives start to grow wing pads and otherwise differentiate from the
worker caste. At each succeeding instar stage, the wings become more fully developed until they are quite well
developed. Another molt and this individual will be a fully developed swarmer capable of mating and forming a
new colony. A new colony does not produce swarmers until after its third year. In an older colony, the transition
from egg to adult usually takes from one to two years. Termites will eat anything made of cellulose. In addition to
wooden members of the house, this includes books, other paper products, and furniture. Any structure can be
easily invaded by subterranean termites.
6. THE DRY-WOOD TERMITE
Incisitermes minor (Hagen)
Termites are called social insects because they live together in colonies. Drywood termite colonies contain three
types of individuals, each of which has its own characteristic appearance and its own duties to perform within
the colony. The colony prospers as a whole because each of the “castes” (type of individuals) contributes to the
welfare of the colony by performing its own duties.
The first types of individuals are the Alates or Swarmers. These are the mature males and females ready to
swarm out to start new colonies.
The second type of individual is the soldier. The main function of the soldier termite is defense of the colony
against intrusion by ants and other enemies.
All the rest of the individuals are nymphs. They perform most of the work of the colony other than reproduction
and defense.
Drywood termites do very well in Douglas fir and all kinds of pine as well as most other woods used in the
structure of houses. They do well in redwood, contrary to popular superstition. They are frequently found “in
nature” in English walnut, eucalyptus, and citrus trees, just to name a few of the ornamental and fruit trees they
infest.
Drywood termites are completely independent of the soil and thus do not have tubes extending to and from the
soil. They can thrive readily in the dry timbers of a structure without requiring any additional moisture. Drywood
termites move with and across the grain of wood.
Drywood termite pellets have longitudinal grooves. These are characteristic of drywood termite pellets and may
be used in identification to differentiate them from beetle pellets which are “smooth”, having no grooves.
7. DAMPWOOD TERMITES
(ZOOTERMOPSIS ANGUSTICOLLIS)
This is the largest species (in size) of termites we will be concerned with. It sometimes will reach a length of one
inch. It is also of the least economic importance of the three termites we are discussing.
In their role as wood destroyers, dampwood termites are associated with excessive moisture conditions. Their
environment is enhanced by the presence of excessive moisture, whether derived directly from the ground as in
a forest situation, from the ground due to faulty construction in the case of a residence, or from a leaking pipe,
clogged roof drain, inadequately engineered cooling system run-off, faulty grade level condition, or other man
made moisture conditions.
Dampwood termites are found along the Pacific Coast from Canada down through California to Mexico.
Infestations are found all the way from sea level to six thousand feet in elevation. Dampwood termite colonies in
the understructures of houses are found in the structural timbers that are, for one reason or another, exposed to
excessive moisture conditions. These conditions might be caused by a simple earth to wood contact as might be
found where a supporting post for an outside porch extends directly into the soil or when a structural beam
underneath the house is directly in contact with the soil of an earth filled porch. Sometimes these colonies are
found under the bathroom area where a leaky bathtub or toilet produces a continuous or frequent source of
moisture. An excessive moisture condition under the house may even be caused by inadequate ventilation due
to lack of or insufficient number of foundation vents to allow free circulation of air.
Dampwood termites, like drywood termites, do not have a true worker caste in their colonies. The work of the
colony is performed by nymphs which later become either soldiers or swarmers (male or female). Swarming
occurs from July through October, usually occurring around September.
The queen will lay from 6 to 22 eggs at a time, averaging 12. The second lot is laid the next spring. Although the
queen of this species is not a great egg layer, some colonies are known to have up to 4,000 individuals. This is
probably due to a large number of supplementary reproductives being present in the colony.
The tunnels of these insects are of many sizes and shapes, having a velvety appearance in the runways. This
surface may be covered with dried liquid feces. The pellets are deposited in dumps or clusters in the galleries
usually and may have a slightly hexagonal shape. The color of the pellets will vary with the type of wood being
eaten. The pellets have a great resemblance to dried coffee grounds. This insect will eat sound wood as well as
damp wood.
