This simplified model of a termite life cycle indicates the three castes: the reproductives, the soldiers and the workers.
Termites are hemimetabolous insects (insects having the three distinct stages of: egg, nymph, and adult).
The poorly understood concept of caste determination does not seem to be definitive or too rigid. Once the caste of an individual is determined, development into other castes is still possible. Soldiers might turn into workers, or even into reproductives, if there is a shortage of individuals in those castes. This process is controlled by pheromones which are chemical signals that trigger a natural response in another member of the same species.
In the case of the queen, there is a specific ‘queen’ pheromone, preventing other individuals from turning into queens. Only if the queen is removed or dies, does the lack of the specific pheromone promote the development of a new queen.