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ANTS
Communication, Pheromones,
Behavior and Organization
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Ants have been around for a long time, all the way to the Cretaceous period with the dinosaurs. Today we have roughly 10,000 described species, but there may be more like 15,000.
Ants are very successful insects. Their combined worldwide biomass is probably equal to the human race. In the tropics of Brazil, their biomass is roughly four times the biomass of all other vertebrates in the jungle. They live and thrive in a variety of habitats from boreal forest, to jungle and desert. Ant colonies can have tremendous populations. The number of workers in established colonies can match or surpass the number of people in greater Los Angeles. A super-colony of Formica genus ants in Japan may number close to the population of the United States!
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harvester ant mound
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Ants aren't so successful by accident. They utilize division of labor to effectively feed their colonies, and modify the surrounding environment for their benefit. Leafcutter ants are farmers that grow fungi crops on leaves they harvest, while weaver ants sew leaves into homes. Many ants are well developed foragers, such as the harvester ants, Pogonomyrmex genus, who are hunter gatherers. Further aiding the harvester ant is its venomous sting, which the author has experienced first hand.
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harvester ants hunting prey
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harvester ants, Pogonomyrmex
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While many ants are hunter gatherers, some tend, or "milk", aphids for their honeydew. Ants accomplish this by stroking the aphids' rear ends with their antennae until they produce a drop of sugary liquid. Ants defend the herd from outside invaders and enemies such as spiders and ladybugs. They even transport their slow moving cows to new feeding locations, and in some instances back to the ant colony where the aphids can survive the winter months.
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ant milking aphids
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Nearly all ants are eusocial, having reproduction dominated by few of the colony members, cooperative care of their brood, and an overlap of adult generations. A benefit of this structure is that colonies are well-defended against enemies by a well established worker class. Because of this, ant colonies are able to control resources and prosper for long periods of time. Ant queens can live up to 100 times the life span of solitary insects the same size due to this stability.
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One reason for the success of ants is their division of labor. Sometimes this manifests in physical differences among worker class, or physical polymorphism. A good example is the African army ant where the smallest workers are only 1% the mass of the soldiers. Some well known polymorphic ants would include the leafcutters, Atta genus, and carpenter ants, Camponotus genus. Physical polymorphism is actually in the minority of species though, only accounting for 20% of them. Most ants exhibit monomorphism within the worker class, but there are still divisions of labor and assignments. One species of monomorphic ant typically lives in a small space, so small that a worker could cover it all in about a minute. Yet, workers will remain in set spots or zones within the nest, working on specific segregated tasks. They're so dedicated to this structure that in the event the nest is destroyed, the workers can reconstruct their own work zone organization.
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Myrmicinae ant carrying dead carpenter ant
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In many ant species, younger workers spend their time at the center of the nest where it's safest, tending to the queen and eggs. As the ants age, they take up tasks further out. The oldest ants carry out the most dangerous work, foraging for food outside the nest where they are more likely to meet their doom. However, it has been determined that in many ants, the correlation between age and task is not so strong, where the division of labor is quite flexible. Age may influence what a worker does, but they may revert to old tasks if needed. Therefore, age isn't the organizing principle in division of labor for many species.
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carpenter ants with pupae
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carpenter ant with prey
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Ants communicate with one another in a variety of ways, but the most important medium used for signaling would be chemicals called pheromones. Often used to mark trails to food, pheromones can be very effective. Spread for maximum efficiency, just one milligram of the pheromone used by Atta texana, a leafcutter ant, would allow the ants to follow one other around the world three times!
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A good deal of ant pheromones are complex mixtures of many chemical compounds. Ants need to know that they're working for their home colony, and need to be able to recognize intruders. Recognizing nestmates is another function of ant produced chemicals. These compounds are spread around the colony by grooming and the sharing of liquid food. Some ants obtain slaves from other colonies by capturing them as larvae or pupae. When the kidnapped ants emerge in adult form, they imprint on the scent of the enslaving colony, tricked into thinking it's their home. Despite the use of these chemicals to determine friend or foe, there are a number of infiltrating arthropods that survive within ant colonies. There are types of mites and rove beetles that thrive among their ant hosts.
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harvester ants attacking beetle
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In summary, the family Formicidae are one of the most successful inhabitants of our planet. We would do well to continue in their study.
Andrew Williams / CritterZone.com
Literature cited
Carde, Ring T. 2003 Encyclopedia of Insects Academic Press pgs.29-32
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