Graveyard or High Rise?
When the first European explorers travelled overland to the top end of Australia they were astounded when they were confronted with the extraordinary structures. These elongated termite mounds are all aligned on a north-south axis. Hence the name of their inhabitants, the ‘magnetic’ termites (Amitermes meridionalis). It has long been a mystery just how and why these insects align their homes with the poles of the Earth, but there are some explanations.
Termites are often referred to as ‘white ants’ because their skin is so thin you can see through it. This also means they are extremely vulnerable to drying out. For such a delicate insect the magnetic termites live in a pretty tough environment, with temperatures soaring during the day and plummeting at night, on top of that everything gets sodden during the wet season. Other termite species will escape the heat by burrowing down but this is not an option for the magnetic termites. They require a home above ground, safe from the annual floods associated with the wet season. The structure of the mounds keeps the termites’ feet dry on rainy days and provides sufficient space for well-ventilated food storage.
North to South
Living in a wedge shaped tower may be great for food storage but if the tower is orientated to catch the suns heat it will turn into a solar cooker. The right architecture helps the termites to keep their homes comfortable, at a constant temperature and moisture level. Around noon, the sun is strongest. But since the mounds are long and skinny and pointed north-south, just the edge of the mound faces the sun at that hour. That gives the mound a narrow profile to the sun at that particular time of day and keeps the termites from getting overheated.
So how do these little termites know how to build north to south?
As the termites are completely blind it’s pretty sure they do not use the position of the sun to guide them in building their mound in a north-south alignment. Scientist suspected that the termites have a build-in compass to guide them. To test this theory researchers artificially changed the direction of the magnetic field by using magnets and voila! The termites dutifully followed and built their mound in the alignment of these magnets instead of the Earth’s magnetic field. It has been suggested that they do this by means of magnetite in their tissues, as has been shown in other animals, such as dolphins and pigeons that orient themselves without access to visual guides.
The termite mound houses the colony and provides a protected place to breed, care for the young and store food. Individual termites are not all the same, but belong to different castes that have specific roles. At the entrance you find the Soldier termites with their large jaws and heavy armour which they use to protect the colony against invaders, most likely ants. Then there are the Worker termites, the labourers of the colony that form the bulk of the termite population. They build the mound, care for the young or gather food. Amongst the workers you’ll also find Nymphs; these are the reproductive termites before they become sexually mature. At the base of the mound you will find the King and Queen in the ‘royal chamber’. The Queen, with her expanded abdomen is enormous compared to the other termites. Her every need is being met by the Worker termites as she is producing eggs for the colony. The King is less flashy and hard to distinguish from the other Nymphs.
One night at the build up towards the wet season, between October and December, you may also encounter termites with wings. These are the reproductive termites called Alates. Once a year they launch a massive armada as they fly out from the colony looking for a mate. Only a small percentage of the Alates will actually manage to pair and they’ll return to the ground, shed their wings and become king and queen of their own colony. Most of the Alates will be consumed by hungry birds, reptiles, mammals or even fish. In fact, many native animals’ reproductive cycles coincide with this yearly feast meal. By the following morning only the wings blowing over the planes are testimony of last night’s massacre. Perhaps I am looking at a graveyard after all…