It's time for another episode of The Termite's Corner! This time we will focus on a small genus from the Macrotermitinae subfamily, the famed fungus growers.
Ancistrotermes is a small termite genus with a marked polymorphism, having two forms of workers and two forms of soldiers (call them "sizes" would be reductive), but none of them reach 5 mm in lenght. They used to be classified under the genus Microtermes, so called in virtue of the small size of its species (contrasting in both a semantic and biological way with the related but much larger Macrotermes), however quite recently they have been reclassified under their current genus. This is due to a few differences when compared to Microtermes: all Microtermes have monomorphic soldiers, while Ancistrotermes have bimorphic ones; Microtermes soldiers have slightly oval or (in the case of some African species) even rectangular head, while Ancistrotermes' have a round one, in addition to sporting more apically curved mandibles. Like all Macrotermitinae they are absent from the new world: the species represented in this post's picture hail from Thailand, whose most notorious Ancistrotermes (though obviously not the only one) is A. pakistanicus, an animal with a very broad distribution, from Pakistan to south-east Asia.
The main castes in Ancistrotermes are primary royals, workers and soldiers. As the name implies, workers are entrusted with all of the colony physical burdens except combat, and as said they come in two forms: the majors and the minors. Aside from a superior overall size, the majors also posses a proportionally much larger head, well suited to chew on plant material or grab large quantities of building soil, and due to this appears much bulkier than their minor colleagues. However, their differences are not just physical but also behavioural: while the major workers routinely exit the nest to forage and also undertake the heavy building, the minors manily remains inside the termitary and care for the brood, royals, soldiers and fungus. The former are also much more present and vigorous in reparing a nest breach, though the latters often help them, for in such an occasion there is no time to spare!
The soldiers posses an hardened orangy head and thin, curved mandibles that they use to defend their colony. Like the workers they are bimorphic, consisting of minor and majors, and again like them these two forms they behave differently, but kinda in reverse: minor soldiers are more active and accompany major workers on their exloring and foraging, while majors mainly remain in the nest, thus someone uncovering foraging Ancistrotermes would be usually confronted with only one form of each caste. This is not a strange thing, for in other Macrotermitinae like many Macrotermes major soldier mainly defend the nest while the minor accompany the foragers outside. The particularity of the Ancistrotermes two soldier forms is another: while in every termite genus with bimorphic soldiers known to me, from Schedorhinotermes to Longipeditermes, there is a clear and evident morphological and/or size difference between the two forms, in Ancistrotermes they are uncannily similar to each other in both factors. In fact, they are so similar that at first glance a layman could not even think that they are actually bimorphic, especially in the field! In addition the major workers in noticeably more imponent than both of the soldiers, a fact considered the norm in nasute termites but quite unique in mandibulated ones.
Like in all termites the primary royals are well sclerotized, equipped with large compund eyes and matured with two pairs of long membraneous wings: they will need them to fly away from the parent colony to try to found their own during. Like in many ants, large quantities of winged royals are periodically released from a mature nest to assure the continuation of the species; but unlike ants, where the male drones mate with the winged female outside the founding chamber and then dies, in Ancistrotermes (like in all termites barring sporadic cases of asexual reproduction) the dealated female will seal herself in a secluded spot along with (usually) a single still very and likewise dealated alive male, and only then mate with him and found along her neo-king.
As we said before Ancistrotermes, like all of its subfamily, rely on the cultivation of symbiotic fungi of the genus Termitomyces to feed; and let me tell you, their fine architectural capacities can account for a very "spoiled" fungus! In fact the fungus require a very specific environement to correctly grow, not only regarding temperature and humidity but also air composition, along with the costant attentions of a multitude termite workers: if devoid of its caretakers, a termite fungus garden will be invaded ad taken over by other saprophytic fungi frighteningly fast. The symbiont fungus is cultivated on special combed structures called fungus combs, made with cellulose and termite excrements, that also house many of the colony's nymphs. These combs are provided with a costant supply of plant matter, and produce tiny white nodules that the termites feeds upon, along parts of the colonized comb itself. Thus, in order to keep their farm productive, Ancistrotermes needs to exit the safety of its nests and forage for suitable cellulose, and do so under the protection of underground tunnels or quite robust above ground shelter tubes; every food source located is likewise quickly covered in soil before harvesting begins. Unlike other fungus growers, Ancistrotermes (and Microtermes too) build many small comb chambers quite isolated from the each others. They seems to be shy termites: in fact, in the case of a large breach occurring in one of their comb chambers they will quickly evacuate it through narrow and quickly sealed tunnels , abandoning their former comb and reliying on the others for substainace while one or more substitutes are under construction.
Now a pic from Doctor Jan Sobotnik, from the University of Prague (CZ):
Here we have all of this Thai Ancistrotermes' castes (except for the primary royals of course): two major workers in the middle, one minor worker on the left, two minor soldiers at the bottom and one major soldier at the top. The soldiers' peculiarity are also clear: note how similar in both morphology and size the minor and majors are, and how the major workers is more imponent than both of them:
