How Ant Colonies Develop

From birth to death, an ant colony is a female-dominated society. Perhaps that's why they're so successful. It's something to think about.

A man disturbed from a deep sleep by a rumble from his stomach decides an early morning sandwich might provide some relief. Stumbling through a dark house, he makes his way into the kitchen and flips on the light. Rubbing his eyes, he opens the fridge and begins to assemble the necessary ingredients for a "Dagwood-style" sandwich. Pulling slices of bread out of the bag, he notices through a sleepy blur that the bread has black specks on it that move. Ants! Hundreds of them! The drawer where the bread is stored is full of ants and a long, black trail winds its way from under the cabinet and back across the kitchen floor. "I've never seen an ant in my house before," he says aloud. "Where in the heck did all these ants come from?"

Many a homeowner and more than a few pest management professionals have likely asked themselves this same question. Ants are the most numerous multicellular organism on earth, especially in the tropical regions of the world. How are ant colonies formed and how do they develop? This topic is complex and has been studied by many myrmecologists (ant scientists) throughout the centuries. Even so, much is still to be learned because differences are seen among the 10,000 plus species that inhabit the earth. This article will examine, in as much detail as possible, the factors responsible for colony development.

MATRIARCHAL SOCIETY. An ant colony is a female-dominated society, with males appearing only periodically for colony reproduction periods. A colony starts small, usually with only one fertilized queen or a few workers with one to a few queens. At this point, the colony is very vulnerable. It has only a certain amount of available labor and resources to invest in colony growth. The life cycle of an ant colony is a series of "energy investments" depending on the colony's needs. For several years, most of the energy is invested in the production of more workers. More workers result in the acquisition of more resources (energy). At some point, the colony reaches maturity, where it is possible to invest a significant portion of its energy resources toward colony reproduction — the production of winged reproductives in the case of most ants.

An ant colony life cycle can be divided into three stages: (1) the founding stage, (2) the ergonomic stage, and (3) the reproductive stage.

Founding Stage. In this stage, new colonies are started following a nuptial, or mating, flight. These nuptial flights are used to intermix winged males and females from various colonies with the purpose of fertilizing the females (queens). Following fertilization, the queen locates a suitable nesting site, constructs a nest cell, and then raises her first brood or batch of offspring.

In the case of some ant species, founding colonies are created when a few workers and fertilized queens leave an established colony to venture out on their own. This group locates an acceptable nest site and begins the work of colony growth.

Ergonomic Stage. In this stage, all the efforts of the colony are devoted to increasing the size of the colony as quickly as possible. Energy resources are focused on producing more workers, not in producing winged reproductives for colony dispersal. If these reproductives were produced too soon by the colony, the ability of the colony to thrive and survive could be threatened.

Reproductive Stage. This stage occurs when the colony has matured to the point where the increase in workers become more of a drain on energy resources than of benefit to the colony. All animals eventually feel the need to propagate and ant colonies are no different. All the previous work of the colony was focused on reaching the point where enough reproductives could be produced so several would eventually survive mating, nest site selection, and colony foundation to create a successful new colony. Edward O. Wilson and Bert Holldobler stated in their book, The Ants, "Like flowering plants, they (ants) issue a crop of seeds, then return to an interval of purely vegetative (i.e., worker) growth."

COLONY FOUNDATION. Depending on the species, ant colonies may have only one queen (monogyny) or multiple queens (polygyny). A new colony founded by a single fertilized queen is called haplometrosis. Founding by multiple queens is referred to as pleometrosis.

Monogyny can be either primary or secondary. In the case of primary monogynous foundation, one queen starts the colony, but in secondary monogyny, several queens start the colony but only one queen survives. Likewise, polygyny has two forms. With primary polygyny, several queens exist from the beginning to found the new colony. In secondary polygynous foundation, a single queen is the foundress, but new queens are added later by adopting or merging with other colonies. Secondary polygynous foundation is seen with the Argentine ant.

New colonies may be started independently by reproductives only (nuptial flights) or by "swarming." In our industry, the term "swarming" has always been used to describe the nuptial flights of ants (and termites). In myrmecological terms, "swarming" refers to the process commonly called budding, but is also referred to as hesmosis or sociotomy. Two types of swarming are noted in the ant world. Budding occurs when a group of workers leaves the nest with one or more queens. Fission occurs when the colony divides into two or more parts, as seen with the pharaoh ant following treatments with residual insecticides.

NUPTIAL FLIGHTS. The life of a winged female ant reproductive is precarious at best and fraught with danger. In fact, very few of the thousands of winged reproductives produced by ant colonies survive to successfully mate and establish their initial nest cells. Of the successful established nest cells, many — if not most — fail to thrive and eventually mature. The greatest danger to these reproductives lies with predators, particularly insects and especially other ants. Birds, lizards, toads, and other animals also take their toll. Heat, desiccation, and failure to locate suitable nest sites also eliminate some ant reproductives.

Nuptial flights are generally timed to coincide with favorable environmental conditions to enhance the potential success of the fertilized queens. Typically, the temperature will be warm but not too hot, and a significant rainfall will have occurred in the past 24 hours. Soil moistened by rain is easier to excavate for nest cells, and the higher humidity lessens the potential for desiccation.

Mating flights occur at all times of the day, but a few species will take flight during the hottest part of the day. For example, Lasius neoniger, one of the most abundant ants found in open fields in the eastern United States, swarms in late afternoon. Mating flights of the Texas leaf cutter ant, Atta texana, occur during the early morning hours of 3 a.m. to 4 a.m. In both species, these flights will begin shortly after a good rainfall. The Argentine ant, Linepithema humile, times its nuptial flights near dusk during the last rays of available sunlight.

Two recognizable mating flight patterns or "syndromes" occur with ants: (1) the female calling syndrome and (2) the male aggregation syndrome.

Female Calling Syndrome. Winged, and often wingless (in some species), queens crawl from an established nest site along the ground or onto low vegetation and release a pheromone that "calls" prospective males to her location. This behavior is seen most often with species that have small colonies and thus do not have the available energy resources to use in producing numerous winged reproductives. An unusual variation of this syndrome is seen with the Florida harvester ant, Pogo-nomyrmex badius, where the winged females cluster around the nest entrance and call the males to them. After mating, the females fly off to locate suitable nesting sites.

Male Aggregation Syndrome. This syndrome is the most widely used form of propagation seen with ants. Males from many colonies will gather at a specific site and release a pheromone that attracts females to the site. The site is often associated with a landscape feature, such as a clearing, a hilltop, the tops of trees, or even the top of a building.

With many species, the males cruise in swarms of individuals at a certain height above the ground. The females fly into this swarm and a fierce struggle to mate ensues among the males. Males successful in coupling with one female will then reenter the fray to seek additional females. Females, likewise, will often mate with several males. In this manner, the genes of the various colonies are intermixed, thus maintaining the gene pool stability of the species. Interestingly, in some species, such as one species of big-headed ant, Pheidole spp., of the desert southwest, the females gather together in an aerial swarm and the males fly into the swarm to mate.

The height of the mating flight above the ground plays a role in the distance the fertilized females will disperse. Males of the red imported fire ant, Solenopsis invicta, for example, fly at a distance of more than 700 feet above the ground. The females have been reported to land as far away as six miles, but the normal distance is about one mile. Species that swarm less than 50 feet above the ground will disperse only a few hundred feet.

In order to mix the reproductives from different colonies, the nuptial flights of these colonies must be synchronized to some degree. In fact, the colonies within a given area often have an uncanny ability to release their reproductives on the same day, at the same time of day. Such synchronization also ensures mixing of the gene pool by bringing together reproductives from different colonies. This phenomenon is poorly understood but may be related to environmental cues, as well as the instinct of the species.

Pheromones also play a role in synchronization. For example, in the carpenter ant, Camponotus herculeanus, the reproductives gather around the nest opening and mill about waiting for a cue. Workers will even drag back to the group errant reproductives that try to wander off. Eventually, a few males will take flight and will then release a pheromone from their mandibular glands. This pheromone stimulates the others to take flight and most likely may stimulate the alates of nearby colonies to take flight.

COLONY GROWTH. The ergonomic stage comprises the greatest portion of a colony's life cycle, often taking many years to complete. Once a queen has successfully mated, she lands on the ground, in the case of soil-nesting ants, or possibly in a tree, in the case of tree-nesting ants such as the carpenter ant. Once on the ground, the queen sheds her now useless wings and begins seeking a suitable nesting site. Soft, moist soil is preferred, especially underneath an object that affords some protection from the elements, such as a log or stone. A carpenter ant or acrobat ant may seek a tree hole, dead limb, or a log.

The queen excavates a nest cell in which she will raise her initial brood. In most species, the nest cell is sealed and the queen does not venture forth. This behavior is known as claustral and serves to protect the vulnerable queen and her precious first batch of offspring from predators and parasites. The nest cell is only breached by the first batch of workers, who begin expanding the nest and foraging for food. In some species, the queen is partially claustral, meaning she will occasionally leave the nest cell to forage for food. Typically, this behavior is seen in more primitive ant species.

Once the nest cell is constructed, the queen begins metabolizing her useless wing musculature and fatty tissues to produce her first batch of eggs and food for the new larvae. The food often takes the form of trophic eggs that are unfertilized and are produced for the sole purpose of feeding the larvae. Feeding also will occur through specialized salivary secretions produced by the queen. After the first workers begin foraging for food, the queen typically ceases production of trophic eggs and focuses her energies on laying fertilized eggs. In one important structure-infesting species, the white-footed ant, Technomyrmex albipes, trophic eggs play a major role in the colony food cycle throughout the life of the colony.

The workers that emerge from this first batch of larvae are called minims and are usually very small in size. Major workers and other worker sizes (forms) are produced later as the colony grows. Minims are generally timid in nature but perform all the duties required by the colony: nest enlargement, foraging, nursing the new brood, caring for the queen, and even, if necessary, the defense of the colony.

Wilson and Holldobler state, "A newly founded colony should strive to maximize the number of workers and their initial survival rate to the expense of everything else." The minims are small because the queen has a limited amount of food available to produce her first brood. A secondary reason, however, is also at work.

As the above quote emphasizes, the numbers of workers is very important. A certain number of workers is needed to adequately complete each of the tasks necessary for the colony to survive. By producing more — but smaller — workers, the queen enhances the completion of the work necessary for the foundling colony's survival. One study showed that minims are less efficient workers, one to one, than their larger sisters, who are produced later. The same amount of minims, by weight, as larger workers yields more minim workers, and it is found that the same amount of work can be completed. The reduced efficiency of the minims is overcome by numbers.

In pleometrotic situations where multiple queens found the new colony together, the colony often reverts to one queen after the minims have emerged. The queens battle each other until one survives. This behavior is often seen with the red imported fire ant. In one study, when multiple fire ant queens were introduced to a group of queenless fire ant workers, the workers killed all but one queen.

At the point the minims emerge, the queen usually reverts to a strictly egg-laying machine. It is at this point that the ergonomic stage really kicks in. All work is devoted to increasing worker numbers as quickly as possible. Enlarging the nest provides space to rear more and more larvae. More food provides the nutrients needed to raise healthy larvae. More workers also improve nest defense against invaders, especially ants from rival colonies of the same or different species.

Foraging outside the nest is the most dangerous task performed by workers; therefore, this work is usually handled by older workers nearing the end of their lives. Younger workers stay closer to the nest, and the youngest workers typically engage in nursing activities. Some ant species, however, possess specialized worker types that perform specific tasks. These specialized workers are produced when the colony grows larger, and are seen most often with advanced ant species.

A colony's ultimate survival is greatly enhanced once it successfully produces a third worker generation. At this point, there are enough workers to perform all the required tasks and to overcome the unexpected loss of workers to predators or other causes.

In many ant species, the colonies become polygynous and additional queens are produced along with the workers. Many of the structure-infesting species have polygynous colonies including the Argentine, pavement, pharaoh, ghost, odorous house, and crazy ants. In some species, hundreds, even more than one thousand, queens may ultimately be produced.

The multiple queens usually cooperate with each other, and their numbers exponentially increase the ability of the colony to grow. The queens of a few species, however, are not tolerant of each other. For example, a colony of the carpenter ant, C. herculeanus, may have several queens, but each will maintain a separate, widely-spaced territory within the nest. This behavior is known as oliogyny.

The growth of the colony proceeds rapidly and only ceases to slow down when the colony size nears maturity. The pace of this growth depends on the availability of resources and competition from other ant colonies of the same or different species. The ultimate number of workers at maturity is species-dependent.

The length of time to reach maturity is often a function of colony size. It takes a certain length of time to build 100, 1,000, or 100,000 workers. Species with a very small colony size can mature within a year. Structural pest species are often larger and take several years to mature. For example, the red imported fire ant reaches maturity at about 220,000 workers, which takes four to six years to achieve. Some carpenter ant colonies can take six to 10 years to mature.

REPRODUCTIVE STAGE. Once an ant colony has matured, it now has sufficient resources to produce winged males and females and enter the reproductive stage. The numbers of virgin winged reproductives produced depends on the species. Smaller colonies, of course, produce fewer reproductives. At the appropriate time, as discussed earlier, these reproductives leave the colony to find mates and renew the process. To an ant colony, this stage of the colony life cycle is the most important because the perpetuation of the species is at stake. Every egg deposited by the queen, every piece of soil removed, every bit of food gathered, every worker sacrificed in defense of the colony has occurred to reach this point.

Once the winged reproductives leave the nest, the colony does not die. It simply begins preparing to repeat the process the following year. The colony continues in the reproductive stage until its ultimate demise from a competing ant colony, unfavorable environmental conditions, or in the case of structure-infesting species, the treatments of a pest management professional.

Article by Stoy Hedges, Manager of Technical Services for Terminix International, Memphis, Tenn.