Among the many hundreds of thousands of astonishing organisms with which we must share this earth, there is one seemingly ordinary group of specimens which fascinates many people beyond all others. There is nothing too extraordinary in the proportions or appearance of ants, but it is their history and culture that induces a second look. These insects are about as different from us mammals as two organisms can be, yet it appears that of all the known animals their way of life appears closest to our human way of life. The similarities in the ways in which we organize our lives are astounding. Ants are doubtlessly the most successful of all the social insects of the Hymenoptera, an order also including wasps and bees.
The earliest known specimens are found entombed in the Scandinavian Baltic Amber samples which scientists date in upwards of 100 million years old (The Ant Colony Œ89). These primitive samples have evolved into the 5000 to 10000 species known today which vary amongst themselves as widely as the numbers suggest (Social Insects Œ68). These remarkably adaptive creatures are found in some form on all continents and all habitats but the extreme arctics. Their success is manifested in the claim that at any time there are at least 1 quadrillion living ants on earth(Groliers Œ93).
All species of ants are social. They live in organized communities or colonies, which may contain anywhere from a few hundred to more than 20 million individuals. These are organized into a complex system which may contain two or more castes and sub castes which can be roughly organized into three groups. Queens, males and workers.
The queen is much larger than the other ants, and has wings until mating. Her primary task is to lay eggs for the colony. Some colonies have one queen; others have up to 5000. Queens develop from fertilized ordinary eggs, nobody is exactly certain what causes these to develop into queens but it is generally thought that the process comes from an altered diet in the pupae and larvae stages and as a pheremone response, which will later be discussed. Queens have an extended life span of up to 25 years and can lay millions of eggs in that time (Ant Colony Œ89).
Male ants are winged as well; their sole purpose is to mate with the queens. For this reason they are the shortest lived ants in the colony. Hatching in the spring, they mate in the summer and upon completion of this task promptly die. As in all Hymenoptera, they are formed from non-fertilized eggs (Social Insects Œ65).
The majority of the ants in the colony are wingless females who are generally non-reproductive. These ³workers² must perform the tasks of sustaining the colony and all life therein. They are responsible for building, repairing, and defending the nest, and for caring for the queen and the brood. They also generate a source of nutrition and feed all the members of the colony. Some will perform a single task for their whole lives, while others change constantly.
In polymorphic species, where the workers vary in size, the worker sub casts are most distinguishable. Here there is found a larger or major worker often referred to as a soldier. Her function is often associated with specialization such as guarding the colony, carrying heavy loads, or in species where necessary, foraging for food. While the minima or smaller workers tend the larvae and queen.
Once or twice each year, commonly on a warm summer day, every ant colony becomes the source of great excitement. Well rested and cared for young alates begin to make for the escapes and exits from deep within the colony. Large soldiers guard the door as the young winged members are escorted to the open by hordes of workers. Suddenly, yet unbeknownst to man nature gives a signal. Soldiers retreat, and workers make space and assemble on the ground as the males and queens are hustled to the sky. Hastening into the air they often meet with winged¹s from other colonies with the same objective. For the first and only time in their lives they will mate, often in mid-air or settling on leaves and branches. Now the queen is equipped with a lifetime supply of sperm. After a brief hour or two of this nuptial flight they return to the ground. Males having accomplished their duty die, while the queen’s task has only begun. She will return to her original colony, inhabit another established colony or form her own.
Not all queens will survive this lonely dangerous task. Her first objective is to shed her wings, for she will never fly again. She breaks them off herself, or is aided by worker ants. If she is to form her own colony she goes about finding a spot. Depending on her species any wide number of sights may be chosen. In the majority of cases a queen will tunnel a cell underground. She uses her jaws and forelegs to move the earth. Alone and unprotected she seals herself into her new home. Then, following a variable gestation period she lays her eggs. It may be nine months before the first workers hatch (A closer Look Œ75). She must find food in this time when she is all alone busily laying eggs. Her body is able to break down her no longer needed wing muscles from which she may gain nutrition. Often she must eat some of her eggs to survive (Groliers Œ93).
The first ants that hatch are workers. This first group is consistently smaller than workers to come. As you will find out they did not receive the same nurturing that will become standard for the brood in a fully functioning ant colony. They instinctively venture out to find a way to feed their feeble mother. From now on, she will be cared for as true royalty, licked and fed by the nurse workers, her only job, to lay a lot of eggs. Once she has been attended to, these busy workers will go about the task of enlarging and enhancing the anthill. First they will provide a place for the brood. Those that live in the earth tunnel chambers in the soil, these are logically referred to as nurseries. Here the eggs and smaller larvae are cared for.
Insect development consists of three stages. The first of which is the egg. These are carried to nurseries as soon as they are laid. Each chamber differs in temperature and humidity. In order for the eggs to develop properly the eggs must have a temperature of 77 digrees F(Colony Œ89). Nurses move the eggs from room to room. These chambers are often found in the deepest recesses of the colony. By licking them the sticky ant saliva causes the eggs to cluster together, for easier carrying. After 14 days this first stage is complete as the tiny larvae hatch (Colony Œ89). These larvae lack legs and eyes and hardly resemble adult ants. The helpless infants rely on the nurses to feed and clean them. This developmental stage requires a temperature of 82 degrees F with a high humidity, as a result the larvae are stuck together and carried about just as the eggs are(Colony Œ89). They receive a special diet as well. For the next 8 to 20 days the larvae grow quickly (Colony Œ89). So quickly, in fact, that they will grow right out of their skin. ³Bursting at the seams,² they slither out as do snakes. When this has taken place four or five times they enter into the third stage and pupate. The larvae excrete a white solution which quickly solidifies upon contact with the air. This is spun into a protective cocoon, which looks very much like a large egg. For an unknown reason, there are a number of larvae which go through pupation without a cocoon. Their colorless legs and antennas are pushed helplessly to their bodies, giving the same appearance as their counterparts within cocoons. In a dry location of 86 degrees F, they finish up their childhood near the surface of the anthill where they may be seen from the outside. After two to three weeks in the cocoon the transformation is complete. Gnawing a hole from the inside, the nurses are alerted of their condition and aid them in escape. For the first few days the exoskeleton has not hardened so the young ant’s body is soft. It¹s chest (thorax) is light brown, legs are pale, and heads and abdomen are gray. Still vulnerable, if they are in danger, they are swept to safety by nurses.
The body of an ant is divided into three segments which are the head, thorax, and abdomen. On the head are antennae, eyes, and mouth parts. The tiny feeler like antennae are perhaps the Swiss Army Knife of the insect world as they enable the ant to touch, taste, smell and sense vibrations. These antennae are also used to help the ants communicate with each other.
All worker ants have two compound eyes, these sense organs are made of many lenses set close together, each lens seeing a tiny part of what the creature is looking at , the combined effect is a fragmented picture of the whole object. This means of vision is beneficial to the ant because it enables them to very easily see movement. Males and queens do not, however, need such a complex system. They have three simple eyes on the top of their heads called ocelli which distinguish between light and dark(Groliers Œ93). The two primary mouth parts are mandibles and maxillae. Mandibles are a moving jaw like apparatus. These are used for fighting, digging and carrying objects. The smaller maxillae reside behind the mandibles and chew food. On the front of the maxillae is a row of tiny hairs which operate like a comb to clean the legs and antennae.
The middle section is called the thorax, here the heart is located, as are three pairs of legs. The wings of unmated queens are attached here as well. Two tiny hooks on each leg enable the ant to climb vertically and upside down. Some, use the front claws to tunnel underground. A tiny row of hairs on the front legs serve the same purpose as those on the maxillae.
There are two pieces which make up the abdomen, the waist like petiole and an enlarged segment which is called a gaster. The petiole is made up of one or two movable segments with humps on top and connects the gaster to the thorax. An ant’s gaster contains a crop and intestine. Some varieties may also contain a poison gland, filled with formic acid that can be sprayed at a moment’s notice. This substance has proven very useful to people as it may be used as an insecticide, antibiotic, preservative, and disinfectant. Ants were originally the sole industrial source but it can now be artificially produced. Contact with minimal doses of the ants product is not harmful to humans but the mass doses of thousands can suffocate a person (Colony Œ89).
Ants digest liquids only. Chewed food is moved to a pouch just below the mouth, contractions squeeze the juices out and they are swallowed. Solids are regurgitated, and liquids are stored in the crop. Now when the ant is hungry, food from the crop will travel through a small valve to the intestine where it can nourish the body. The crop lies just within the gaster and has thin elastic walls. A full crop is large enough that this process can happen several times before the food supply is seriously depleted.
Due to the many specialized roles in the ant community not all members are in charge of the important task of gathering food. As a result these gatherers must feed the other members of their community. The means employed to accomplish this task are unique and intriguing. A hungry ant uses its antennae and legs to tap and stroke a food gatherer on the head. Following this signal the two ants will put their mouths together and food is passed from the crop of the gatherer to the hungry member, this is called mutual feeding or trophallaxis. An ant with a full crop can be distributed food to 8-10 others in this way. And as they share their supplies one ant can feed up to 80 others (Groliers Œ93).
Ants have an elaborate system of communication, which includes visual, auditory, tactile, gustatory and olfactory signals (Groliers Œ93). While eating, many animals socialize and communicate. Few, however, are able to learn so much from their meals. Modern science has discovered the importance of this method of feeding. While people used to believe that ants were able to work together as they do because they were highly intelligent insects. We now know that this is not the case. Although they are capable of learning, ants as individuals are not particularly intelligent at all. Secretions received from the food share tell the ant what to do. These substances come from secretions the ants have picked up by licking the body of the queen and her brood. Nest mates constantly feed, lick and touch each other so these secretions are passed all around the colony. These vital secretions act as memos in a large office building. Because each colony has its own individual scent, they help ants to identify each ot
her by smell and touch. They tell an ant everything from what jobs need doing in the nest, to communicating excitement and danger. Special glands enable various ants to give off an alarm secretion, lay trails and attract sister workers to a new food source, this Olfactory communication is made possible through the release of chemicals called pheromones. So it is not special intelligence which enables ants to communicate as they do but the passing of and ability to react to secretions, which keep up a bond between colony members and helps them work together.
Across the many different species there are various specialized colonies and means of nesting. While in the majority of cases ants live in the soil or wood or any number of natural cavities. Some nomadic army ants may form temporary nests, or bivouacs, consisting entirely of ants themselves a living suspended ball (A Closer Look Œ75). Other ants build ³carton nests² of plant tissue. African weaver ants make their nests of living leaves bound by larval silk. Others form a symbiotic relationship with Acatia trees eating from the plants and guarding against other destructive insects and competitive vegetation.
Many ants also have specialized ways of obtaining food. Nomadic army ants raid and retrieve in groups, these large species live predominantly on other organisms. They forage en mass and are therefore able to overtake much larger prey.
Fungus growing ants are highly specialized herbivores that ³ cultivate subterranean fungus gardens on fecal or plant-derived substrates.² These ants live solely on fungus. ³Leaf cutters² gather green leaves, which they chew and grow fungus on.
Harvester Ants feed on seeds. Living in hot dry climates they construct elaborate nests up to 2m below the earth devoting massive chambers entirely to the storage of seeds, which are often topped off with a layer of gravel and sand, as the ancient Egyptians protected their grain supplies. Harvesters often husk collected seeds before storing(Groliers Œ93).
Gatherers and herders, gather plant liquids directly from wounds and nectaries. Others collect honeydew, a substance excreted by aphids which feed on plant juices. The aphids are unable to digest many of the nutrients from these juices which are beneficial to the diets of the ants. Thus, in exchange for protection from enemies the ³cow² allows the ant to feed off of its excretions.
Perhaps the most interesting however the parasitic are and slave making ants. Two or more species may form joint nests in which the broods are separated, and the parasitic species obtains food from the host species. In another category called mixed colonies, the broods are mixed and cared for as one. Some parasitic ants are permanent residents of the host colony and are so specialized that they have lost the work caste. Here slave making may result. But perhaps the most blatant exploitation made by one species over another found in nature aside from we humans is the slave-making species. These raid other colonies and steal worker pupae that they enslave to carry out the work of their colonies. Some species, such as the ants of the Amazon are so specialized for capturing slaves that they cannot forage for food or care for their young. Without slaves they quickly perish.
Ants are often called the most fascinating insects of all. While they can be vastly destructive, stripping valuable trees bare in the tropics, and a general nuisance marching through kitchens and pantries they are extremely helpful to man as they help to clear the earth of pests like termites. Wood ants clear forests of millions of tree-destroying insects over a single summer. They have been here for approximately 53 million years, and 56 percent of genera represented among the extensive Baltic amber are living today, and show no sign of dying out soon. In our great pursuit of knowledge it is my hope that we can derive something of value from studying the culture and life-style of the hardest working organisms in the world. (With the exception, of course, of the Villanova biology teachers)