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Ants

ants

There are over 8,800 species of ants in the family Formicidae -- all of them are eusocial (although some "slavemaking" species no longer have a worker caste).  There are more species of ants than all other social insects combined.  They are also the most ecologically diverse group in terms of distribution, life history, feeding strategies, and specialized adaptations.  As a group, ants consume a wide variety of food, but individual species usually tend to specialize:  some are primarily carnivores, some gather seeds and grains, while others concentrate on sweets (nectar and honeydew).

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Reproductive
Caste

Queen  -  Fertile adult female and foundress of the colony.

Drone  -  Fertile adult male - develops from an unfertilized egg.

Worker
Caste

Adult females, wingless and unmated - generally the daughters of the queen. Some individuals may exhibit morphological specialization for certain tasks within the colony (e.g. soldiers, honey pots, etc.).

Although we usually think of an ant nest as an underground labyrinth of interconnecting chambers and tunnels, there are also many species that live above ground in shrubs, trees, or dead wood.  Pharoah ants will nest in the corner of a desk drawer and fire ants will nest inside electrical utility boxes.  A typical nest contains at least one fertile egg-laying queen, hundreds or thousands of adult female workers, a nursery for rearing eggs, larvae, and pupae, a storage area for food reserves, and a disposal site for waste and dead bodies.

Most new colonies are founded in late spring or early fall after an annual "swarming" event in which hundreds or thousands of winged ants (virgin males and females) emerge from their nests and fly into the air for the purpose of mating.  After returning to earth from this nuptial flight, the male wanders off and dies.  The new queen sheds her wings and scouts around for a suitable homesite.  She lays a small clutch of eggs and cares for them until they mature into her first batch of workers (all females).  Thereafter, the queen devotes herself to laying eggs while the workers forage for food, care for the young, and enlarge the nest.

queenant

In some species, each nest contains only a single queen (monogyny) while other species may have several queens living together peacefully in the same nest and sharing in egg production (polygyny).  In single-queen colonies, all of the workers are sisters so there is a selective advantage for mutual cooperation.  Death of the queen, however, will result in death of the colony because the workers have no way to replace their queen.  In multiple-queen colonies, the death of a single queen has less impact.  New queens may be adopted or adjacent colonies may join together.  Colony survival is maximized at the expense of individual queens who gain no selective advantage if their own daughters are rearing the offspring of another queen.

In some ants, all workers are similar in size and appearance.  But in other species, workers may vary in size and some individuals may have physical characteristics that make them more suited for some jobs than for others.  The smallest individuals, sometimes called minors (or minims), generally work inside the nest caring for the queen or feeding the larvae.  Larger individuals may forage for food or enlarge the nest.  The largest ants, called majors (or maxims), often have huge mandibles and powerful jaw muscles.  They often serve as soldiers, standing guard at the nest entrance, protecting foragers from predation, or defending the colony from raids by other ants.

Pheromones play an important role in the social organization of an ant colony.  Alarm, appeasement, social cohesion, recruitment, and trail marking pheromones are among the list of semiochemicals that have been reported in ants.  Each colony also has a distinctive taste or odor which members use to identify nestmates and exclude invaders.  Regulation of caste is not well-understood.  Apparently, all female eggs are identical when laid.  Whether they mature into minors, majors, soldiers, or new queens depends on the care and feeding they receive as they grow and mature.  To some extent, this may depend on the needs of the colony as manifested through feedback loops involving photoperiod, food supply, temperature, and many other variables.

Types of ants.   With more than 8,800 described species, ants are the most ecologically diverse of all social insects.  The following list includes some of the more common groups.

leafcutters
  • Harvester ants usually live in arid environments and feed primarily on seeds.  Many species build elaborate underground nests that may reach depths of six feet or more.
  • Army ants are nomadic predators that do not have permanent nests.  They include legionary ants which live in South America, and driver ants which live in Africa.
  • Slave-maker ants raid the colonies of other species and steal worker larvae and pupae.  Once the slaves mature, they work for their "owners" until they die.
  • Leafcutter ants (also known as parasol ants) are gardeners.  They chew up plant leaves into a pulp and use it to fertilize a fungus they grow for food in underground gardens.
  • Weaver ants build nests in trees.  Workers interlink their bodies, pull branches into position, and tie the leaves together with silk spun by their larvae.
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  • Honey-pot ants feed on honeydew excreted by aphids.  Some workers engorge themselves with food reserves until their abdomens swell to the size of marbles.
  • Fire ants are an invasive species with a very painful sting.  They respond aggressively to any disturbance of their nest.
  • Thief ants are very small.  They raid the food supplies of larger ants and then escape through tunnels that are too small for the bigger ants to enter.
  • Carpenter ants build their nests in wood.  Unlike termites, they do not eat the wood but they may still cause serious damage to homes and other wooden structures.

Social Insects

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