Another way to see termites is to break open their
tunnels. Workers are blind and follow chemical trails
laid down by other workers. They will continue to pass
en masse along an opened tunnel, though some will
eventually repair it. The termite queen (or queens—
some species have multiple queens) is located deep
within the nest and cannot be seen unless the entire
nest is dissected. Queens are immense compared with
workers and soldiers. Virtually immobile, weighed
down by an enlarged, gourd- like abdomen, the queens
pass their lives producing the colony’s eggs, while
workers attend to their needs.
Termite species typically digest the cellulose in wood
with the aid of the collective metabolism of mutualistic
flagellate protozoans and bacteria inhabiting their
hindguts. Once cellulose is reduced to simple sugar
molecules, termites gain nutrition from the process of
gut faunal and floral metabolism (much as ruminant
mammals do). Removal of the protozoans will prevent
a termite from digesting cellulose and other large
molecules of wood. The termite, the bacteria, and
the protozoans are obligate symbionts, an example
of a complex coevolutionary mutualism (chapter 10).
The flagellate protozoans gain fitness by inhabiting
the termite, which provides continuous food, shelter,
and a means of dispersal. The very hard wood we
find in many tropical trees is perhaps an evolutionary
response to selection pressures posed by continuous
termite herbivory.
Termites do not feed just on wood. Many species
are essential decomposers of forest- floor litter. A study
in Amazonia by Christopher Martius showed that
termites, which collectively attain a biomass of 2,000
kg per hectare (1,800 lb/ac) and number in excess of
1,000 individuals per square meter (10.75 ft^2 ) of forest
floor, feed on somewhere between 20 and 50% of the
forest’s fallen leaves. Termites chew up leaves as they
pass them through their digestive systems. This action
increases leaf surface area and enhances the microbial
film, facilitating continued decomposition.
Termitaria, the termite nests, form patches of
high nutrient concentrations in otherwise nutrient-
poor tropical soils. A study conducted along the
Río Negro in Venezuela by J. Salick and colleagues
showed that termites consumed between 3 and 5% of
the annual litter production, transporting it to their
termitaria. Termitaria contained more nutrients than
litter, and litter was more nutrient- rich than the soil.
When termites abandon termitaria, which they doregularly— nest rate abandonment averaged 165 nests
per hectare (65/ac) per year— these sites form patches
of high nutrient level ideal for many tree species.
Termite activity has a potentially important influence
on nutrient cycling and tree establishment in this area
of nutrient- deficient soils.
Many termites feed on soil, including in their intake
various soil- inhabiting fungi. The actions of soil-
feeding termites are believed to help release nitrogen
and phosphorus, contribute to humification, improve
soil drainage, and help aerate soil, as well as increase
exchangeable cations such as calcium and potassium.
Termites are so abundant in the world’s tropical areas
that they may contribute to global climate warming
by enhancing the greenhouse effect. Their collective
digestive abilities produce significant quantities of
atmospheric methane, carbon dioxide, and molecular
hydrogen. Forest clearance and the conversion of forests
to agricultural ecosystems often result in increased
termite abundance, thus accelerating the production
of these atmospheric gases. On the other hand, some
areas that have experienced forest clearance or have
been converted to uses such as banana plantations
appear to have lost termite diversity and biomass.
In any case, when you happen upon a termite nest or
mound, pause, look at it, and consider what a remarkable
and venerable group of insects termites happen to be.Plate 6- 18. A Rufescent Tiger- Heron (Tigrisoma lineatum)
perched atop a termite mound in southern Brazil. Photo by
John Kricher.chapter 6 essential dirt: soils and cycling 93