The soldier caste is responsible for defending and protecting the colony from enemies (which are mainly ants). They have protruding jaws and larger, armored heads than the workers, which are often a shade of yellow, orange, brown, or red. The soldiers of some species have snouts instead of jaws in which they squirt a repellent liquid at invading ants. Termite soldiers may be either male or female.
Unlike ants which are all capable of fighting, termites have the soldier caste who’s purpose is solely that, as the worker termites do not fight. The percentage of soldiers vs workers in a colony varies from species to species; it may range from 10-30%. Whenever there is a breach in the walls or tunnels of the nest or feeding sites, soldier termites will head to the breach once they detect a change in the temperature and proceed to block the gap, often by forming a phalanx. In many species, they will also rattle their heads against the ground to alert the other termites of the danger. I’ve heard this sound many times, and it may be quite elaborate, like a synchronized crescendo at times.
The higher families of termites often have soldiers in large and small sizes (major and minor soldiers); otherwise known as dimorphism. The large (major) soldiers are relatively slow moving due to their large size, and mainly do “heavy duty” defense duties. The small (minor) soldiers have added duties of directing the worker traffic, and are suited to defend the colony against small species of ants, which the large soldiers typically have problems against.
Soldiers are unable to feed themselves due to their elongated jaws, and need the workers to feed them constantly. Some species have soldiers which (in my opinion) seem ineffective in their role of defending the colony. For example, the Pericapritermes have jaws that are designed to flick ants away, but it also frequently ends up flicking the soldier away too! Other species have soldiers which have poor aggressive qualities, even appearing meek, and appear to be largely ineffective in their defense duties.
In some species of termites, the soldiers not only bite, but also release a fluid from their stomachs when they bite. I’ve observed this is in Odontotermes and also Coptotermes. In Coptotermes formosanus (Formosan termites) and other species of Coptotermes, the soldiers release a white sticky liquid identified as naphthalene from their gullet, when they bite. It quickly depletes them of energy, and their jaws often get locked up afterwards. They normally do not release their grip once they have bitten, but if they do release, they become really weak and likely die soon after if not attended to by any workers. Such “suicides” are also observed in the Globitermes sulphureus soldiers, which “pop” themselves to release sticky liquid after biting their targets. Picture below shows a pair of Coptotermes curvignathus soldiers, similar to Formosan termites (Coptotermes formosanus), with a pair of sharp mandibles.
The ranges of defense methods employed by the myriad species of termites are fascinating, and sometimes seem highly ingenious. Some species of termites have soldiers which resort to a passive defense by blocking tunnels with their odd shaped heads. Such defense is called phragmosis. They just use their heads to plug up tunnels. If one soldier falls, another soldier takes its place.
Termites generally have a highly evolved use of chemicals and pheromones. The nasute species resort to chemical warfare by squirting either a repellent or sticky liquid from a snout on their heads, which ants find unpleasant. Other species of termites even go to the extent of being able to determine the threat level of certain ant species based on the semiochemicals or “smell” that they release. Some ants with “friendly” chemicals do not elicit an aggressive response. The advantage of this is that some ants and termites actually co-exist together in a semi-symbiotic relationship, and thus are able to avoid “friendly fire.” Such chemical defense methods of Nasutitermes termites have been highly successful, so much so that many species are able to openly forage during the daytime in the open, and from my observations, ants seem to avoid them.