Tag Archives: ants

Miles From Home: How Ants can Navigate Long Distances (and back!) to Forage

Ants are well known for their extraordinary ability to find food, and bring back enough to feed their vast social organisations. Being able to form relationships with other organisms that digest food, carry objects 50 times their weight and achieve great feats of communication and learning all help them forage… but how exactly do they find their way? Recent research from the University of Edinburgh has concluded the fascinating story of how the Formicidae navigate.

Plot a Course! Direction of Travel

Ants can decide on a direction for walking by using the position of the Sun in their visual field, as specialised cells in their compound eyes can detect the UV polarised light emitted by the Sun. Ants can maintain the correct course, whilst decoupling information where their body is an which direction they are travelling in. They also make use of visual landmarks (such as leaf litter), olfactory and tactile cues, and some species use the Earth’s magnetic field for navigation. According to the researchers at the University of Edinburgh, the ants construct a more sophisticated representation than they thought possible from the small size of their ganglia (brains), and can integrate information from different modalities (and from different areas of the brain) into the representation of direction.

How Far? Keeping track of Distance

Day-foraging ants, such as those in the genus Cataglyphis, are able to navigate exceptionally long distance (up to 200 metres and back!) by recording the distance they have travelled as well as the direction. An internal pedometer helps the ant remember the number of steps taken and this information is integrated with the ‘optical flow’ of objects moving around their visual field (which is an illusion- of course it is actually the ant that moves). Rather than each ant randomly roving away from the hive in search of food, the successful ‘pioneer’ must communicate the location to her sisters so they can make a sortie to the high quality patch of forage en masse…

neivamyrmex_army_ants_raiding_trail.jpg

Follow the Leader: Scent Trails

The long line of ants that you are bound to see in tropical forests are formed from scent trails that allow them to navigate back home, even if it is 200 metres away and in the dark! The ability to find the shortest route back is a crucial adaptation for avoiding desiccation in hot and arid environments. However, in army ant species, a group of foragers who become separated from the main marching column can turn back and form a circular ant mill, and run round constantly until they die of exhaustion! Ants have also been recorded to carry each other along a route, if an older and more experience forager notices that an internal nest worker (which are less familiar with the outdoor environment) is off the trail.

Final Word

So ants are able to backtrack to the location of their nest using their memories and the Sun as a reference point, and the way they operate is very similar to a self-driving car. This new research gives a unique insight into how brains of ants (and other insects) operate, and will inspire the next developments in robot system building to mimic their functioning, which would especially be useful for robots that need to navigate in forested areas. Modelling the neural circuits in the ant brain will also be useful to simply understanding more about the complex behaviours of the fascinating family of insects.

Further Reading

http://www.cell.com/current-biology/fulltext/S0960-9822(16)31466-X

http://jeb.biologists.org/content/209/1/26

http://science.sciencemag.org/content/353/6304/1155

How do Social Insects make Decisions?

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Using information passed on by others can greatly improve individual fitness, and has been the fundamental mechanism underlying the evolution of social insects such as bees, wasps, ants and termites. However in some situations it is better to ignore social information and for an individual to use its own prior knowledge and experience. So how do these colony-forming insects tailor their reliance on social information for the benefit of the ‘superorganism’? Scientists have recently reviewed the literature and made theories as to the nature of decision making in insects.

Social information is relatively ‘cheap’ to obtain for hymenopteran foragers, because they can bypass the costs associated with exploration and food sources obtained socially are likely to be better quality. In the truly eusocial western honeybee, Apis mellifera, generations overlap so information passed on by the ‘waggle dance’ (movements conveying location and quality of food sources) increases the fitness of that colony. Foraging choice are further refined by chemical cues (pheromone trails) and simply presence of other foragers.

Relying on social information may also incur costs and may not lend an evolutionary advantage. In the case of the ant forager, if she ignores social information she may find a novel food source that will benefit the colony as a whole, whilst a well-used food source is depleted (I.e. exploration produces more up-to-date information). Honeybees that rely on dance information may take time to find a dancer and may need multiple viewing and excursions to find the communicated food source.

A trade-off between these advantages and disadvantages will adjust how often (and what proportion of) social insects rely on social information. All animals tend to display the most profitable information they know, so relying on social information may be more profitable than exploration. For example honeybees only communicate their dance after finding high quality food sources. ‘Social learning strategies’ in animals are genetically determined in response to environmental and social cues. One such approach is the ‘copy if dissatisfied’ strategy, where animals will use social information if their current information is below a fitness ‘threshold’. These optimum social learning strategies can also be acquired (ironically) through social learning.

Grüter, C., & Leadbeater, E. (2014). Insights from insects about adaptive social information use. Trends in ecology & evolution, 29(3), 177-184.