question: how ants determine the path they take between their home and food
comment: A trail of formic acid they left behind like breadcrumbs. They use smell to follow the path.
passages: BULLET::::- Dead reckoning, also known as "path integration," is the process of computing one's position by starting from a known location and keeping track of the distances and directions subsequently traveled. Classic experiments have shown that the desert ant keeps track of its position in this way as it wanders for many meters searching for food. Though it travels in a randomly twisted path, it heads straight home when it finds food. However, if the ant is picked up and released some meters to the east, for example, it heads for a location displaced by the same amount to the east of its home nest.
   When workers find food sources, they communicate this information to the rest of the nest. They use biochemical pheromones to mark the shortest path that can be taken from the nest to the source. When a sizable number of workers follows this trail, the strength of the cue increases and a foraging trail is established. This ends when the food source is depleted. The workers will then feed the queen and the larvae by consuming the food they have found, and regurgitating the food at the nest. Foraging trails can either be under or above ground.
   They integrate this information to find the shortest route back to their nest.
  
  Like all ants, they can also make use of visual landmarks when available as well as olfactory and tactile cues to navigate. Some species of ant are able to use the Earth's magnetic field for navigation. The compound eyes of ants have specialised cells that detect polarised light from the Sun, which is used to determine direction.
   Section::::Overview.
  
  In the natural world, ants of some species (initially) wander randomly, and upon finding food return to their colony while laying down pheromone trails. If other ants find such a path, they are likely not to keep travelling at random, but instead to follow the trail, returning and reinforcing it if they eventually find food (see Ant communication).
   Foraging ants travel distances of up to from their nest and scent trails allow them to find their way back even in the dark. In hot and arid regions, day-foraging ants face death by desiccation, so the ability to find the shortest route back to the nest reduces that risk. Diurnal desert ants of the genus "Cataglyphis" such as the Sahara desert ant navigate by keeping track of direction as well as distance travelled. Distances travelled are measured using an internal pedometer that keeps count of the steps taken and also by evaluating the movement of objects in their visual field (optical flow). Directions are measured using the position of the sun.
   BULLET::::- The participants in a flock of birds or a shoal of fish all maintain their relative positions or alter direction simultaneously due to lateral communication.
  
  BULLET::::- Ants, termites and bees coordinate by lateral communication, mediated in the case of ants and termites, for example, by scent trails. The resulting physical structure is an emergent property of the individual entities.
   Section::::Mechanism.
  
  Studies in arthropods, most notably in the Sahara desert ant ("Cataglyphis bicolor"), reveal the existence of highly effective path integration mechanisms that depend on determination of directional heading (by polarized light or sun position) and distance computations (by monitoring leg movement or optical flow).
  
  In mammals, three important discoveries shed light on this issue.
  
  The first, in the early 1970s, is that neurons in the hippocampal formation, called place cells, respond to the position of the animal.
   In another example, McClamrock cites the case of a man driving from one destination to another. On the way, he encounters various external signals and stimuli (street names, direction signs, people who provide information when asked, landmarks, etc..) and all of these help him, in many cases are indispensable to, his successfully finding his way from point A to point B. The path he ends up traveling to get to point B from point A is, in any case, partially determined by his environment. In the case of ants, this is even clearer. When we look at the tracks that ants make as a result of their movements, they seemed to be highly ordered and preplanned. But, in fact, an ant will usually encounter unforeseen and unforeseeable obstacles as it makes its way along from one point to another. At each obstacle, it will be constrained to make a choice that it otherwise wouldn't. The path that it ultimately travels will therefore be heavily determined by its exterior environment, as well its behavior.
   In short, the use of a combination of simple cues makes it possible for red harvester ant colonies to make an accurate and rapid adjustment of foraging activity that corresponds to the current availability of food while using positive feedback for regulation of the process: the faster outgoing foragers meet ants returning with seeds, the more ants go out to forage. Ants then continue to use these local cues in finding food, as they use their olfactory senses to pick up pheromone trails laid by other ants and follow the trail in a descending gradient to the food source. Instead of being directed by other ants or being told as to where the food is, ants rely on their closely coupled action and perception systems to collectively complete the global task.
   Ants communicate with each other using pheromones, sounds, and touch. The use of pheromones as chemical signals is more developed in ants, such as the red harvester ant, than in other hymenopteran groups. Like other insects, ants perceive smells with their long, thin, and mobile antennae. The paired antennae provide information about the direction and intensity of scents. Since most ants live on the ground, they use the soil surface to leave pheromone trails that may be followed by other ants. In species that forage in groups, a forager that finds food marks a trail on the way back to the colony; this trail is followed by other ants, these ants then reinforce the trail when they head back with food to the colony. When the food source is exhausted, no new trails are marked by returning ants and the scent slowly dissipates. This behaviour helps ants deal with changes in their environment. For instance, when an established path to a food source is blocked by an obstacle, the foragers leave the path to explore new routes. If an ant is successful, it leaves a new trail marking the shortest route on its return. Successful trails are followed by more ants, reinforcing better routes and gradually identifying the best path.
   On its outward journey, it zig-zags right and left. Every time it changes direction, it lifts its head and wheels around to take a bearing on the sun. In addition, it has to remember how far it went on each straight run. When it’s time to head for home, it has to sum all this data and come out with the precise direction needed. Some outward journeys take an ant a quarter of an hour, with sun-sightings every few seconds.
   The neotropical ant "Ectatomma ruidum" is also capable of time-place learning. They can learn to visit a feeding site in the morning, another one at midday, and a third one in the afternoon. They follow this spatio-temporal pattern even when food is withheld on test days. They then stay at the feeder for the approximate duration that food was normally available before moving on, at the right time, to the next feeder. This shows that the ants do not rely on direct cues from the food itself, but use instead a learned association between daily time and place.
  
  Section::::Fish.
   Many mechanisms have been proposed for animal navigation: there is evidence for a number of them. Investigators have often been forced to discard the simplest hypotheses - for example, some animals can navigate on a dark and cloudy night, when neither landmarks nor celestial cues like sun, moon, or stars are visible. The major mechanisms known or hypothesized are described in turn below.
  
  Section::::Mechanisms.:Remembered landmarks.
  
  Animals including mammals, birds and insects such as bees and wasps ("Ammophila" and "Sphex"), are capable of learning landmarks in their environment, and of using these in navigation.
  
  Section::::Mechanisms.:Orientation by the sun.
   BULLET::::- "Telotaxis" requires paired receptors. The movement occurs along the direction where the intensity of the stimuli is stronger. Telotaxis is clearly seen in the movement of bees when they leave their hive to look for food. They balance the stimuli from the sun as well as from flowers but land on the flower whose stimulus is most intense for them.
  
  BULLET::::- "Menotaxis" describes organisms' maintenance of a constant angular orientation. A clear demonstration is shown by bees returning to their hive at night and the movement of ants with respect to the sun.
   BULLET::::- Ants are behaviorally unsophisticated; collectively they perform complex tasks. Ants have highly developed sophisticated sign-based communication.
  
  BULLET::::- Ants communicate using pheromones; trails are laid that can be followed by other ants.
  
  BULLET::::- Routing Problem Ants drop different pheromones used to compute the "shortest" path from source to destination(s).
  
  Section::::A review of lateral-computing techniques.:Agent-based systems.
   When searching for food, primary orientation is when ants are exploring a new terrain without the guidance of odor trails. Secondary orientation is when terrain has been explored, and there are pre-existing odor trails which ants use to orient themselves. When "T. sessile" ants are orienting themselves for the first time they often rely on topography. The major types of elements they rely on are bilaterally elevated, bilaterally depressed, unilaterally elevated, and unilaterally depressed. They use these types of surfaces to orient along, and lay the first odor trails, which can then be followed in the future, to the food source, by other ants.
   The ant appears to use an internal pedometer to count its steps in a harsh environment where odors quickly vanish, enabling it to "count back" to its nest. When stilts were glued on to the ants legs, they overshot the distance of their nests, while ants with cut legs traveled short of their nest. It's suspected that while the ants unlikely have the brainpower to literally count steps, they are somehow doing it intuitively.
  
  Section::::Navigation skills and internal pedometer.:Food memory.
   The wood mouse is the first non-human animal to be observed, both in the wild and under laboratory conditions, using movable landmarks to navigate. While foraging, they pick up and distribute visually conspicuous objects, such as leaves and twigs, which they then use as landmarks during exploration, moving the markers when the area has been explored.
  
  Section::::Path integration.
   Desert ants use sun compass as a reference to the amount of walking distance to their specific destination. Ants, like bees, compensate for the sun’s daily movements as it moves and rotates about the Earth. They communicate to other ants who have already been out and base their directions on the direction they should go. In addition to sun compass, insects such as ants also use a tool called azimuthal position of the sun. These are additional cues determined by ants and passed on to other ants when they communicate.
  
  Section::::Studies analyzing sun compass orientation.
   Ants have been observed sending out scouts to patrol for food items, and coming back for other workers if the food found is too large to bring to the nest by the finder alone, for example a dead caterpillar that is too heavy. This again would involve displacement by communicating outside of the here and now. Recruitment has also been observed by the African Weaver Ant "Oecophylla longinoda" for the purpose of communicating new food sources, emigration to new sites, and for defense against intruders. Researchers have described no less than five distinct systems to fulfill these functions in this species. The ants communicate using a system composed of olfactory or scent clues from several glands together with body movements. The animals will use antennation, body jerking, and/or mouth-opening, and will combine these clues with the application of the scent trails or scent release to pass on information regarding resources or intruders.
   Another measure of learning is spatio-temporal learning (also called time-place learning), which refers to an individual's ability to associate the time of an event with the place of that event. This type of learning has been documented in the foraging behaviors of individuals of the stingless bee species "Trigona fulviventris." Studies showed that "T. fulviventris" individuals learned the locations and times of feeding events, and arrived to those locations up to thirty minutes before the feeding event in anticipation of the food reward.
  
  Section::::Factors influencing foraging behavior.:Genetics.
   Studies of inter-nest pheromone trail networks maintained by super-colonies of Argentine ants ("Linepithema humile") have shown that different colonies establish networks with very similar topologies. Insights from these analyses revealed that these networks – which are used to guide workers transporting brood, workers and food between nests – are formed through a pruning process, in which individual ants initially create a complex network of trails, which are then refined to eliminate extraneous edges, resulting in a shorter, more efficient inter-nest network.
   This skill, which has also been observed in the behavior of foraging honey bees, is elemental to the survival of this species of ant under the harsh conditions in which it lives. This behavior allows "Cataglyphis" to travel farther from its nest than any other creature that lives in the Sahara, with respect to size.
  
  Section::::Navigation skills and internal pedometer.:Pedometer.
   Studies by Wehner in the Sahara desert ant ("Cataglyphis bicolor") demonstrate effective path integration to determine directional heading (by polarized light or sun position) and to compute distance (by monitoring leg movement or optical flow).
   BULLET::::- Foraging: Some ant species recruit fellow workers to new food finds by first tapping them with their antennae and forelegs, then leading them to the food source while keeping physical contact. Another example of this is the waggle dance of honey bees.
  