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BLORF
Join Date: Nov 2003
Posts: 77,746
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kinda. I still need to proofread it for errors, and I need to ask my professor if I need an introduction and discussion section (he lists it as part of the guidlines, but I think it's dumb to have a seperate introduction and conclusion since all that information is just a rehash of stuff that's stated within the body of the work.)
I can do all that tomorrow though. Right now: Freedom!  Ended up being just over ten pages double spaced so call it 11 if I have to add a lamo introduction section.
Also, posting it in case anyone cares enough to read it. 
Quote:
AN OVERVIEW OF THE FORMICIDAE FAMILY OF INSECTS.
The purpose of this paper is to provide a generalized zoological overview of the insect family Formicidae. Ants are a hugely diverse family of organisms with many genera that exhibit unique traits and activities. This paper intends to provide a generalized overview of the majority behaviors displayed by most ant species. Harvester ants were chosen as a model due to both their tendency to display behavior and life cycle patterns typical to most ant species, and the abundance of research material available. Topics covered include the caste system, the phases of colony growth and development, worker tasks and interactions with other colonies, and the basics of chemical communication.
THE CASTE SYSTEM
Nearly all species of ants can be divided into one of two classes, known as castes: worker and reproductive. These castes determine an individual’s morphology and function within the hive. (Gotwald, 1995)
Workers make up the bulk of a hive and perform all the necessary non-reproductive functions to ensure its survival. Many ant species have workers are that are divided into major and minor types, with major workers being larger, stronger, and more likely to assume the most dangerous jobs in the colony, while minor workers tend to stay inside the colony or venture outside only when protected by major workers. Still other species have an even more extreme polymorphism with distinct sub-castes. Of these, some army ant species have up to four sub-castes: minim, medium, submajor, and major workers. (Gotwald, 1995) In most species, workers from six weeks to a year. (Gordon, 1999)
The reproductive caste is equally important to the overall function of the hive, and is composed of a single breeding queen, whose function is to lay the eggs that will eventually become worker ants. Many ant queens can live up to twenty years. (Gordon 1999) As well, the reproductive caste includes unmated queens and male ants, which leave the nest during the summer mating season. These ants do no work other then propagating the species.
GROWTH OF A COLONY
The growth of a typical ant colony generally is described as passing through three distinct stages: The colony-founding stage, the ergonomic stage, and the reproductive stage. (Oster and Wilson, 1978)
The colony founding stage begins with the mating of virgin queens in the summer, after the rainy season, when nutrients are plentiful and the climate is conducive to foraging and nest construction. (Gordon, 1999) Two classes of mating behaviors exist: female calling syndrome and male aggregation syndrome. Ants species which reproduce via female calling syndrome, where females on the ground release a sex pheromone to attract males, are much less common then ant species which reproduce via male-aggregation syndrome. (Daly, et al. 1998) In male-aggregation syndrome species, virgin queens and winged males (known as alates) swarm and cluster into large groups which then land and mate with multiple individuals.
Soon after mating, the males die and the queens depart to found new colonies. (Gordon, 1999) Queens from Pleometrotic species group together to share resources when form a new colony, while more common Haplometrotic species form a nest on their own. Regardless, most colonies eventually end up with a single queen. (Pleometrotic queens may die after the colony is founded, or be ejected from the nest by a dominant queen.) (Sudd and Franks, 1987) Newly mated queens are often prey for birds and small reptiles, as well as ants of both the same species and predator species. Consequently, newly mated queens and new colonies have an exceptionally low survival rate, often less than one percent. A swarm of several thousand queens often produce a couple hundred nests, of which only thirty or forty may survive longer then a year. Queens which swarm in an area populated by younger nests (less than four years) have a higher rate of survival then queens which swarm in areas populated by older nests, as the challenges of competition and predation from younger nests are easier to overcome. (Gordon, 1999)
After mating the queen breaks off her wings and works continuously to dig the first chamber of the new nest, often twelve to eighteen inches deep in the soil. Once the new brood chamber is complete, she blocks off the entrance to the nest and begins to lay eggs, using energy from stored fat-bodies and the now-redundant wing muscles. Once the nest is complete, in many species the queen will never travel to the surface again in her lifetime. This is known as claustral colony foundation. (Sudd and Franks, 1987) After six weeks, the first brood of workers is hatched. These workers are called nanitic workers and are much smaller and weaker then ordinary workers. Their small size allows the queen to produce more individuals with her limited stored resources. Once these workers are mature, they immediately begin to forage food to help the queen produce a second generation. (Gordon, 1999)
Once the queen produces the second generation of workers, the colony enters the ergonomic stage where it experiences rapid growth and development. At this phase, increasing the size of the colony, storing food, expanding the territory used for foraging, and developing the interior underground structures of the colony are all paramount to survival. (Oster and Wilson 1978) After two years in this phase, most colonies will have more then a thousand workers, a strong foraging presence, and a well developed nest. After two years, the mortality rate for ant colonies drops to about five percent and survival for the rest of the queen’s natural lifespan is all but assured barring a major catastrophe to the nest. (Gordon, 1999)
After reaching a well established state, the colony enters the reproductive stage and begins to produce males and unmated queens. The timing of this stage is important to the overall well being of the colony, since early production of alates allows the nest to increase it’s genetic footprint earlier, but for every non-working member of the colony produced, resources are being spent that could be used to help ensure the colonies survival. The time at which this phase is entered therefore is highly dependent on seasonal changes in resources and the quantity and rate at which any given colony has been able to gather resources. (Sudd and Franks 1987)
On average, colonies enter the reproductive stage after five years and with a population of about 10,000 individuals. In many species this population remains fairly constant, as the birth rate of workers slows to match the death rate while the difference is made up in the production of reproductive alates, although in others a single colony can have a population of many millions of individuals. Once alates mature, they mate and the cycle begins again with new colonies. This stage may last up to fifteen years until the original queen dies, at which point the colony slowly enters a phase of decline as the population shrinks and eventually disappears due to the lack of reproduction. (Gordon 1999)
Some ant species, such as the argentine ant, reproduce underground and create new colonies solely by a process known as budding, in which new queens leave with workers of the founding colony and form a sub-colony nearby. (Ingram and Gordon 2004)
WORKER FUNCTIONS
The survival of the hive depends as much on the worker caste as much as it does on the queen, if not more so. Worker ants can be divided into two groups: external and internal. This division is often manifested in some species as a form of temporal polyethism. Any time an ant is outside the nest, it is exposed to various degrees of dangers, be they from predators, other ants, or climatological factors such as dehydration. From the perspective of the colony, therefore, it makes sense that the youngest workers who have the longest potential lifespan remain in safety while the older workers who are more likely to die from physiological old age endanger themselves outside the nest. (Porter, 1981)
The generalized order of tasks for a worker ant as performed chronologically is as follows: Attend the queen, attend the eggs and larvae, assist new adults out of their pupal casings, attend pupae, internal nest construction and maintenance, food storage and exchange. There is a fair amount of overlap between the tasks performed by the various age groups, however, so while an ant of a certain age is most likely to be found at a given task, it may also be observed doing other necessary tasks. (Sudd and Franks 1987) Attending the pupae queen and larvae generally involve grooming, carrying, and feeding.
Some species of “honey pot” ants of the genus Myrmecocystus perform the unique task of becoming living food storage devices. These ants are given honey via trophallaxis and store it within their body for the entire hive regurgitating the honey to other ants who require it. They often clinging to a root or branch or residing in a special chamber within the nest and are often fed so much that their body can swell ten times larger then other worker ants. Once an ant becomes a honey pot ant it performs no other tasks within the nest and is cared for by other workers.
Nest construction involves opening new tunnels and chambers within the underground structure of the nest. Unlike other types Hymenoptera such as wasps and bees, the nest is not cellular and eggs and larvae are kept in large piles inside designated chambers. Likewise, food storage and worker barracks are constructed of similar chambers. These are constructed in underground nests by using the mandibles to carve out large chunks of soil, and compacting the walls of the tunnels and chambers with saliva. In some species the workers produce vibration and sound by rubbing their thorax against one another to help loosen soil. (Spangler 1973) The soil removed is often redistributed throughout the nest and used for other constructions, as soil that has been previously worked is easier to handle. (Hubbard 1974) The same technique is used for nests composed of rotting wood. (Sudd and Franks 1987)
At any given time, there are more ants inside the nests than there are tasks that need to be performed. The ants not doing work are “inactive” ants that spend their time resting and conserving resources. As well, these ants function as a “reserve” force that can come out to work as extra foragers should a particularly rich food source be discovered, or to defend the nest should a predator or rival ant colony attack. (Gordon 1999)
External workers compose on average only twenty five percent of the population, but they perform the most vital tasks that make up the backbone of the colony system: Patrolling, foraging, midden work, and maintenance.
Patrol ants, (also called guard ants) are often the first to emerge in the morning and serve to help protect the other ants working outside as well as the nest itself. They walk in zigzagging trajectories, radiating outwards from the nest and defining the area in which the forager ants will search for food. In species with polymorphic worker sub-castes, the patrol ants often have strong, scimitar like mandibles, larger heads or overall larger body size and are well adapted for fighting. In ant species with “major” and “minor” classes of worker, majors are more likely to perform guard duty then any other task. (Carroll and Janzen 1973)
Midden workers are responsible for removing waste from the colony and depositing it in a communal dump site called a midden. Not all species of ants have a midden, but in those that do, he midden often serves a dual purpose: It’s a way of disposing of unwanted trash, such as seed husks, dead ants, feces, and other detritus, and it also serves as a soaking morass of semiochemicals that serve to mark territory and keep other ants away from the nest. (Wagner et al 2000) Harvester ants and other North American ant species have been observed to forage for charcoal, fossils, and other inedible materials and depositing them in the midden. These materials are porous and are likely used to help soak up these semiochemicals. In experiments where charcoal was removed from middens, it was replaced within seven days, and in experiments where the midden itself was entirely removed, the frequency of invasions from neighboring ant colonies increased dramatically. (Gordon 1984)
External maintenance workers build and maintain the external part of the nest, most often represented in a mounded hill that has the appearance of a crater, which is composed of dirt excavated from the interior of the nest. The shape of the mound is highly variable depending on species and the climate in which they live. In general, species which live in warm and tropical climates that are in danger of flash flooding, build heavily on one side of the nest to deflect water around it, while in cooler climates the mound is usually more evenly distributed. Some European ants build large external mounds which function as summer nest chambers, intercepting a greater amount of sunlight then a flat area. Mounds of species that need to contend with greater levels of animal activity in the area often build around grass stems and roots to increase the strength of the structure. (Sudd and Frankes 1987)
Foragers make up the bulk of external ants and are responsible for gathering food and returning it to the nest. Ants are omnivorous and their diet varies tremendously from species to species, being everything from simple foragers of seeds and plants (such as harvester ants) to being active predators (such as army ants). (Gotwald, 1995) Generally, foragers begin to emerge from the nest as patrolling activity reaches its peak, and foragers stay within foraging areas that have been earlier predetermined by patrollers. When a forager finds food, it carries it in its mandibles back to the nest and deposits it just inside where internal workers will find it and store it. (Gordon 1999)
Forager ants must frequently contend with ants from neighboring nests. In general, colonies in their ergonomic stage tend to have violent its interaction with their neighbors while very young colonies and colonies in the reproductive stage tend to avoid conflict with their neighbors. As well, younger ant colony workers are more likely to continue to forage in a “contested” area where rich resources are abundant, but potentially hostile neighboring ants are also more abundant. Older, better established colonies meanwhile tend to avoid these areas, as well as avoiding fights when they do enter them, possibly due to being in a phase of development where the rapid sequestering of resources is no longer as important to colony survival. (Gordon 1999)
This hypothesis is supported by additional experiments performed by Gordon in which ant colonies were isolated from their neighbors by means of aluminum siding buried in the ground that the ants could not climb. She then mapped the foraging areas of various ages and types of ant colonies in certain areas, and discovered that while all ant colonies reacted the same to the disappearance of a neighboring colony (extending their foraging areas into territory previously claimed by the now isolated colony), younger workers from neighboring colonies aged three to four years (in the upper end of the ergonomic phase) tended to be more tenacious in holding their newly acquired territory, even against colonies that are much larger and older. Colonies that were over five years of age tended to return to their former territory, and weaker colonies younger then one year of age tended to actually lose ground. (Gordon 1999)
COMMUNICATION
Communication between ants is more heavily reliant on chemical signals then other Hymenopterans such as bees, which use body language and dancing to communicate. The chemicals used for communication between insects are known as semiochemicals, or pheromones. All ants of a colony poses a unique chemical marker within the waxy layer of the exoskeletal cuticle that’s known as the “hive scent” or “colony odor.” Members of colonies can recognize other members of the same colony and differentiate them from other members of other colonies quickly and easily by smelling this chemical, which is highly useful in situations in which the workers need to quickly cooperate to achieve a goal, such as defending the nest or raiding another nest. As well, ants are capable of producing many other pheromones from specialized glands found throughout their bodies. (Sudd and Frankes 1987) These pheromones can signal a wide variety of information, from alarm and warning signals to marker signals used in navigation to sex pheromones used in reproduction. (Gotwald, 1995)
Chemical communication has many advantages, such as the ability to function equally well in dark underground chambers as it does in light, the ability to send a message quickly and easily to all nearby members of the same species regardless of ambient noise or disturbances, and the unambiguity of the message being received. It also has downsides: the inability to rapidly give off the same signals over and over once the chemical reserves in an individual’s body are consumed, the tendency for pheromones to collect and linger within an area, and an upper limit on the number of chemical compounds available to use for communication.
Carroll C.R. and Janzen D.H. (1973) Ecology of Foraging by Ants. Annu. Rev. Ecol. Syst 4:237-257
George F. Oster and Edward O. Wilson 1978. Caste and ecology in the social insects Princeton, N.J. Princeton University Press
Gordon D.M. 1984. The harvester ant (Pogonomyrmex badius ) midden: Refuse or boundary? Ecological Entomology Vol. 9, no. 4, pp. 403-412.
Gordon D.M. 1999. Ants at work : How an insect society is organized. New York, NY: Free Press. 182 p.
Gotwald WH. 1995. Army ants : The biology of social predation. Ithaca: Comstock Publishing Associates. 302 p.
Ingram, Krista K. and Gordon, Deborah M. 2003. Genetic analysis of dispersal dynamics in an invading population of argentine ants. Ecology 11:2832:2842
Michener C.D. and Michener MH. 1951. American social insects; New York: Van Nostrand.
Porter, S. D. and Jorgensen, C.D. 1981. Foragers of the harvester ant Pogonomyrmex owyheei: A disposable caste? Behavioral Ecological Sociobiology (9):247-256
Spangler, H.G. 1973 Vibration aids soil manipulation in Hymenoptera. J. Jansas Entomol. Soc. (46):157-160
Sudd JH and Franks NR. 1987. The behavioral ecology of ants. Glasgow; New York: Blackie; Chapman and Hall. 206 p.
Taber SW, editor. 2000. Fire ants. 1st ed ed. College Station, TX: Texas A&M University Press. 308 p.
D. Wagner, M. Tissot, W. Cuevas and D.M. Gordon 2000 Harvester Ants Utilize Cuticular Hydrocarbons in Nestmate Recognition
Journal of Chemical Ecology. Springer Netherlands. 10:2245-2257
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12-03-2006, 11:06 PM
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