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ANIMAL BEHAVIOUR

The behaviour of harvester ants as they forage for food is much like the TCP that controls Internet traffic. Indeed, ants are social species, establishing new colonies and building homes that can put any HVAC system to shame, observes Antony P U

A collaboration between a Stanford ant biologist and a computer scientist has shown that the behaviour of harvester ants as they forage for food mirrors the protocols (transmission control protocols or TCP) that control traffic on the Internet.

That ants and termites are the oldest social insects with their complex societies dating back at least to the early Cretaceous period (about 144 million years ago) needs no introduction. Each colony includes three groups: workers, soldiers and the reproductives. Each group is assigned a specific job to keep the colony alive. The workers gather food; soldiers build shelter and the reproductives produce and tend to the young. The colony’s king and queen are known as primary reproductives, as they are the original founders of the colony.

Reproductives play a particularly important role in creating new termite colonies. In subterranean termite colonies, the role of primaries or winged kings and queens, is to meet, mate and start new colonies. This process is called swarming. Termites whose role is to back-up the primary queen in their colony by producing extra eggs are called supplementary reproductives. Their role is to help expand the colony’s foraging territory, a process called budding.

Building colonies

These roles allow termite colonies to disperse, establish new colonies in any soil environment, and invade other structures in order to find more wood and thus, ample supply of food. Worker termites are white in appearance and navigate with their antennae rather than their eyes; worker termites are blind. This caste of termites is responsible for bringing food back to the colony, caring for the other castes and constructing the galleries and tunnels that form the physical colony. Subterranean worker termites use a mixture of mud, saliva and faeces to create mud tunnels to and from sources of food. Soldier termites are pale yellow-brown in colour and have enlarged heads and mandibles.

The soldiers’ enlarged jaws prevent them from feeding themselves and they rely upon workers to assist them in this task. The sole function of the warrior termite caste is to defend the colony from attacks. These warriors will occasionally attack other termite colonies, although the primary threat to any termite colony is the ant. Reproductive termites are an integral part of the colony’s structure. These insects go on to form new colonies, within which there will be reproductive kings and queens. Considering that they live in soil and are exposed to a multitude of fungi and possible mycotoxins, termites are great survivors. Studies show that queen termites can live up to decades under ideal conditions. Workers and soldiers live approximately one to two years.

Termite towers

The termite is the acknowledged master architect of the natural world. No other insect or animal approaches the termite in the size and solidity of its building structure. The world’s tallest non-human structures are built by Australian or African termites. If a human being were the size of an average termite, the relative size of a single termite nest is the equivalent of a 180-storey building, almost 2,000 feet high. How is it possible that this tiny creature has the engineering know-how to erect an edifice of this magnitude? This knowledge is innate to the termite.

The building material is usually local soil mixed with saliva. Sometimes dung is mixed in. It becomes so hard and impervious that the native people of the area use it for building their mud and stick shelters. The termite mound, or termitorium, consists of hard, thick walls that seal in moisture and keep heat out. The Australian and African varieties of termite towers are designed for cooling. A system of channels and ducts circulates air through the mound. These passageways run through areas of the mound that have walls that are porous or have tiny ventilation holes.

At the lower core of the termitary are the living and working quarters. This area is the coolest and most insulated zone. The royal chamber, the largest chamber in the nest, houses the queen and king. Below the royal chambers are where the workers store food and care for the young termites or nymphs. In some colonies, the workers tend gardens where tiny mushrooms and fungi are grown. The termites grow fungus inside a comb located in several pockets in the central zone of the inner nest.

The comb, made of termite droppings, provides nourishment for the growing fungus and the termites feed on both the fungus and the comb. Termites live on cellulose, which makes the framework of vegetation, and fungi. Ingress and egress from a termite tower is provided by underground tunnels. The tunnels lead outward and branch into a network of passages that open to the outside. Underground wells supply the termitary with water and a source for cooling the interior.

The peaks and towers of the nest act as lungs that expel rising hot air, generated by the breaking down of the fecal comb by the fungus. The air then rises via a large central air duct, and moves up through the long porous chimneys. The carbon dioxide in the air then diffuses to the outside, while oxygen diffuses into the chimneys. The oxygenated air eventually loses its heat to the cooler outside air and cools sinking down into the cellar. Such an ingenious HVAC system is necessary for the survival of some three million termites to a single colony.

When defending their colony, some termites ‘explode’, releasing chemicals that injure intruders. A previously unknown crystal structure has been discovered that raises the toxicity of their chemical weapons. This newly discovered structure is said to allow ageing workers to better defend their colony. When faced with a threat, many termite species employ a type of altruistic suicide known as autothysis in order to deter attackers.