Ants Rely On A Unique Skill To Find Friends Among Trillions of Foes

These insects have some serious olfactory abilities.

by The Conversation, Stephen Ferguson and Laurence Zwiebel
Ants help biting green leaf to build nest - animal behavior.
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Ants can be found in nearly every location on Earth, with rough estimates suggesting there are over ten quadrillion individuals — that is one followed by 16 zeroes, or about 1 million ants per person. Ants are among the most biologically successful animals on the planet.

A surprising part of their evolutionary success is the amazing sense of smell that lets them recognize, communicate, and cooperate with one another.

Ants live in complex colonies, sometimes called nests, home to a wide range of social interactions. Here, one or more queens are responsible for all the reproduction within that colony. Most colony members are female workers — sisters that never mate or reproduce and live only to serve the group.

Ants need to defend their colony, seek food, and take care of offspring. To accomplish these tasks, some ant species domesticate other insects, while others create agricultural systems, harvesting leaves from which they grow edible fungal gardens. Successfully coordinating all these intricate tasks requires reliable and secure communication among nestmates.

We are biologists who study the remarkable sensory abilities of ants. Our recent work shows how their societies depend on the exchange of reliable information which, if disrupted, spells doom for their colonies.

Unique scents

A colony of carpenter ants (Camponotus floridanus) reared in the Zwiebel Lab at Vanderbilt University.

LJ Zwiebel, Vanderbilt University

Human communication relies primarily on verbal and visual cues. We usually identify our friends by the sound of their voices, the appearance of their faces, or the clothes they wear. Ants, however, rely primarily on their acute sense of smell.

An exterior shell, known as an exoskeleton, encases an ant’s body. This greasy coat carries a unique scent that varies from individual to individual and gives each ant a unique odor signature that other ants can detect. This odor signature can communicate important information.

The queen, for example, will smell slightly different from a worker and thus receive special treatment within the colony. Importantly, ants from different colonies will smell slightly different from one another. The detection and decoding of these differences are vital for colony defense and can trigger aggressive turf wars between colonies when ants catch a whiff of intruders.

For ants and other insects, receiving chemical information begins when an odor enters the tiny hairs located along their antennae. These hairs are hollow and contain special receptors, called chemosensory neurons, that sort and send the chemical information to the ant’s brain.

Odors, such as those given off from an ant’s greasy coat, act like chemical “keys.” Ants can smell these odor keys only if they are inserted into the correct set of chemosensory neuron “locks.” A neuronal lock remains shut to any odors except its particular key.

When the correct key binds to the correct neuronal lock, though, the receptor sends a complex message to the brain. The ant’s brain is able to decode this sensory information to make decisions that ultimately lead to cooperation between nestmates — or battles between non-nestmates.

Changing the locks

Scientists messed with ants’ sense of smell to observe how it impacts group behavior.

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To better understand how ants detect and communicate information, we use laboratory tools such as precisely targeted drugs and genetic engineering to manipulate their sense of smell. We are especially interested in what happens when an ant’s sense of smell goes wrong.

For example, when we prevent an odor “key” from opening a chemosensory “lock,” it contains the chemical information from reaching the brain. This would be like plugging your nose or standing in a completely dark room — no scents or sights would register. We can also open all the “locks” simultaneously, which floods the neurons with too many messages. These scenarios dramatically compromise an ant’s ability to detect and receive accurate information.

When we messed with ants’ sense of smell — whether shutting down or flooding their odor receptors — we found they no longer attacked non-nestmates. Instead, they became less aggressive. Without clear information, ants exercised restraint and opted to accept rather than attack their fellow ant. Put another way, ants ask questions first and shoot later.

We believe this social restraint is hard-wired and gives ants an evolutionary advantage. When you live in a colony with tens of thousands of sisters, a simple case of mistaken identity or miscommunication could lead to deadly infighting and societal chaos, which is potentially very costly.

When ants in our experiments lose their sense of smell and their ability to detect accurate information becomes compromised, they no longer stick together in a cohesive colony.

Not only do they fail to recognize and attack foes, but they also stop cooperating with their friends. Without nurses to care for the young or foragers to collect food, the eggs dry up, and the queen goes hungry.

We discovered that without an accurate means of communicating and receiving chemical information, societies collapse, and the colony quickly dies. Miscommunication or the lack of accurate information affects other highly social animals, including humans, as well. For ants, it all depends on their sense of smell.

This article was originally published on The Conversation by Laurence Zwiebel and Stephen Ferguson at Vanderbilt University. Read the original article here.

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