Capitolo La biologia, lo studio della vita

Fire ants have a good defense

Fire ants have a red to reddish-brown color, but even so, they most likely take their name from the ability to sting. Their stinger protrudes from the rear, but in a split second, they can grab the skin of a person with their mandibles and position the stinger between their legs to sting from the front. The stinger injects a toxin into the tiny wound, and the result is a burning sensation. The next day, the person will end up with a white pustule at the site of the sting. The success of this defense mechanism is clear because most animals, including humans, try to stay away from bees, wasps, and ants, and any other animal that can sting.

Living usually in an open, grassy area, fire ants sting in order to defend their home, which is a mound of soil that they have removed from subterranean tunnels. They use the tunnels to travel far afield safely when searching for food, which they bring back to their nest mates. The queen and many worker ants live in chambers within the mound or slightly below it. The queen is much larger than the other members of the colony, and she has only one purpose: to produce many thousands of small, white eggs. The eggs develop into cream-colored, grublike larvae, which are lavishly tended by worker ants to keep them clean and well fed. When the larvae become encased by a hard covering, they are pupae. Inside a pupa, an amazing transformation takes place, and eventually, an adult ant breaks out. Most of these adults are worker ants, but in the spring, a few are winged «sexuals», which are male and female ants with the ability to reproduce. The sexuals remain inside the colony with nothing to do until the weather is cooperative enough for them to fly skyward to mate. A few of the fertilized females manage to survive the perils of an outside existence long enough to start another colony.

All of the ants in a colony have the same mother, namely the queen ant who produces the eggs. The workers are sterile, closely related sister ants. Because of their genetic relationship, we can view the members of a colony as a superorga-nism. The queen serves as the reproductive system, while the workers serve as the digestive, urinary, and, indeed, all the systems that keep the superorganism functioning. What fosters cooperation between the members of the superorganism? The answer is pheromones, chemicals secreted externally that influence the behavior and even the development of other species members. Fire ants, like other ants, produce several different pheromones that send messages when released into the air. The message could be «food is available» or «be alert for possible». The queen even releases pheromones that cause workers to attend her.

Why does it work, in a biological sense, for these sisters to spend their lives working away slavishly, mostly raising more sterile sisters and defending the colony with little regard for their own safety? It works because the few sexual females that survive their temporary existence on the outside pass the co-lony’s joint genes on to future generations in new and different places. Any social system that allows an organism to pass on its genes is a successful one from an evolutionary point of view.

▶ Which is the biological role of the queen in fire ants colonies, as in many other social insects, like bees?
▶ Why can we consider a fire ant colony like a superorganism?
▶ What are the biological advantages of a social organization in fire ants, like in other animals?

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