The termite queen is one of the few creatures of the animal kingdom that demonstrate extreme physogastry or the expansion of the abdomen to an extreme size. This phenomenal growth is largely due to distended ovaries and fat deposits inside her abdomen. Some ant queens also display physogastry, but I can’t think of any creature that rivals the termite queen, in terms of size to body ratio.
Not all termite species develop such an extreme form of physogastry; for example, drywood termite queens only have minimal enlargement of their abdomens. It mostly depends on the age of the nest and its size; the larger the nest, the larger the queen.
In Macrotermes natalensis (in Africa), the queen is possibly the largest among termites (6 inches or more long), but all of the larger Macrotermes species can attain huge size as well (roughly 4 inches upwards). It is believed that in some species, the queen can have a lifespan of 10-50 years – NB: Personally, I doubt anyone has ever studied and monitored the lifespan of a long lived termite queen from start to finish!
Both king and queen termites start out the same size - at swarming time, when they are called alates or swarmers. However, after they have shed their wings, excavated themselves a chamber (sometimes called the copularium) and mated, the queen slowly starts to increase in size.
This increase in size will eventually result in the queen termite transforming into a veritable egg laying machine, capable of laying hundreds, and even thousands of eggs a day, although this only applies for those species that typically develop into very large colonies. Unlike ants, termites need to mate periodically, and this (fertilizing the queen every now and then) seems to be the only role of the termite king.
The sole queen and king termites are the heart of the colony, although some species may have secondary queens and kings as well. Most species house the queen and king in a special cell called the royal chamber/cell, usually located in the central part of the nest. The royal chamber is a special cell with thicker walls on all sides, and has many outlets to allow a steady stream of workers to move in and out to tend to the queen, and also carry off her eggs the moment they are laid.
At all times, there is always an army of workers tending to the queen, feeding her, carrying off her eggs to be deposited in the nurseries, and licking her, mainly for the purpose of maintaining the delicate pheromone balance within the colony. Basically, the queen and king “rule” over their nest via pheromone signals. The king is also well taken care off by the workers, but he is confined to the royal chamber all his life.
Some species do not seem to have very well defined royal chambers, and this trait is often seen in species which do not develop large nests, have multiple queens, or have a widely spread and loosely defined “nest” consisting of smaller sub-nests all over an area.
In countries where termites are abundant, termite queens are occasionally eaten as a delicacy and aphrodisiac. This mistaken belief probably stems from the size of the queen and indeed, the queen is most probably highly nutritious; all the same, there is likely no scientific basis for its supposed aphrodisiac properties (in much the same way as rhino horn being an aphrodisiac).