How Tunsian Desert Ants Smell in Stereo

Cataglyphis ant in the Ebro Depression in Spain

Biological Strategy

Desert ant

Anika Hazra

Image: José María Escolano / Flickr / CC BY NC SA - Creative Commons Attribution + Noncommercial + ShareAlike

Sense Light (Visible Spectrum) From the Environment

Living systems constantly receive signals from their environment that help them survive. Light (in the visible spectrum) can come from other living systems (such as fireflies) or from non-living sources (such as the sun). Survival often depends on sensing and responding to challenges like low light conditions or light that has been altered in some way. Because basic survival is at stake, living systems must excel at meeting those challenges. A well-known phenomenon is how water bends light. A stork trying to catch a fish underwater can compensate for this bending effect so that when it strikes at the fish, it has a good chance of catching it.

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Sense Chemicals (Odor, Taste, etc.) From the Environment

Chemicals are important for signaling and communication among living systems, either intentionally (such as when two living systems try to find one another) or unintentionally (such as when a plant emits a chemical signal that an herbivore can use to find a tasty bite). They are also important for other uses, such as navigating or finding sources for minerals. But chemical signals are often relatively weak and disperse when moving through water or gases. Therefore, detecting them requires specialized abilities, including a way to determine where they are coming from. A well known example of sensing chemicals can be seen in ants following a pheromone trail laid down by others in their colony to locate a quality and abundant food source.

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Navigate Over Land

Organisms that navigate over land must avoid obstacles and find their way from one point to another. Because land lies at the interface of the ground and air, these organisms have the opportunity to use signals transmitted through both the ground or air, rather than relying on one potential source. To take advantage of this opportunity, these organisms must have strategies attuned to diverse signals, which may travel through multiple media. An example of an organism that navigates over land is a desert ant in Tunisia that senses smells from two different directions at once, forming a “mental map” of its surroundings.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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The antennae of the Tunisian desert ant create a detailed olfactory map by detecting smells in left and right channels.

Introduction

A species of desert ant in Tunisia, Cataglyphis fortis, travels long distances through the country’s saltpans in search of food. Returning ants orient themselves to their nest entrance using both visual and scent-based landmarks. A desert ant knows it has found its way back home by remembering the scent around its nest entrance, with its two antennae acting as its homing device.

Close-up of Cataglyphis fortis head and antennae

Image: Estella Ortega / AntWiki / CC BY SA - Creative Commons Attribution + ShareAlike

Frontal view of a Cataglyphis fortis ant’s head, including its simple and compound eyes and antennae

The Strategy

This desert ant needs the extra help to find its way back to its nest after a foraging trip because it can travel more than 100 meters (328 feet) away from its nest in search of food. While visual landmarks may be useful in directing an ant back toward the general vicinity of its nest entrance, the entrance itself is inconspicuous without its scent marker.

In addition to visual landmarks, these ants use path integration, which is a mental map that tracks the direction and distance of the ant’s travels, and results in an estimate of the path the ant needs to take to get back to its starting point from its current location. This map can be thought of as a series of paths an ant knows to follow to find its way back home—even without any landmarks or points of reference—and they are constantly being updated while an ant is out foraging.

Path integration is not always the fastest way to get home since it doesn’t involve exploring more efficient routes, but it is reliable.

Perhaps even more fascinating than path integration is the map of smells the ants create and commit to memory. Odors are memorized according to whether they come from the left or the right of the ant throughout its previous return journeys from foraging. It has been experimentally proven that ants lacking use of one of their antennae are incapable of following their map of smells to return home. This means that the antennae are working together to pinpoint the source of a scent, much like how separate left- and right-channel speakers allow us to better determine the apparent source of a sound.

The Potential

Olfactory detection could be useful in homing devices, such as those in self-driving vehicles or vehicles that are operated remotely and which might lose access to other navigational cues. Building the ability to create and remember olfactory maps into homing devices, in addition to their use of visual landmarks, would improve their effectiveness and efficiency in finding targets.

Path integration offers a model for navigation. This could be particularly significant for rescue devices searching through unmapped and potentially dynamic environments such as wreckage and rubble.

Last Updated January 1, 2022

References

“The ants memorize the olfactory topography, that is, which odours are positioned on the right or the left side during the ants’ home-bound runs.” (Steck et al. 2010:943)

“Unilaterally antennectomized ants could not pinpoint the nest within a two-dimensional array. Hence, this kind of orientation depends on the simultaneous input of both antennae, that is, on a stereo sense of smell.” (Steck et al. 2010:939)

Journal article

Do desert ants smell the scenery in stereo?

Animal Behaviour | 2010 | Kathrin Steck, Markus Knaden & Bill S. Hansson

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