The Role of Smell in Ant Societies: Binding Forces and Unity
Ants can be found in almost any place on Earthas rough estimates suggest there is over 10 quadrillion individuals – that’s a 1 followed by 16 zeros, 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 incredible sense of smell that allows them to recognize, communicate and cooperate with each other.
Ants live in complex colonies, sometimes called nests, that are home a wide range of social interactions. Here, one or more queens are responsible for all reproduction in that colony. The majority of colony members are worker sisters who never mate or reproduce and live only to serve the group.
Ants must defend their colony, looking for food and takes care of the offspring. To accomplish these tasks, some species of ants domesticate other insects, while others create agricultural systems, collecting leaves from which grow edible mushroom gardens. Successfully coordinating all these complex tasks requires reliable and secure communication between neighbors.
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 that, if broken, spells doom for their colonies.
Unique aromas
Human communication relies primarily on verbal and visual cues. We usually recognize our friends by the sound of their voice, the look of their face, or the clothes they wear. The ants, however, rely primarily on their keen sense of smell.
An outer shell, known as the exoskeleton, surrounds the body of an ant. This greasy fur carries a unique scent that varies from individual to individual and imparts to each ant a unique odor that other ants can detect. This smell signature can communicate important information.
The queen, for example, will smell a little different than the worker and will therefore receive special treatment in the colony. Importantly, ants from different colonies will smell slightly different from each other. Discovering and decoding these differences is vital to the defense of the colony and can cause aggressive turf wars between colonies when the ants smell the breath of intruders.
VIDEO: Deadly aggression between enemy ants
For ants and other insects, the acquisition of chemical information begins when an odor enters the tiny hairs located along the length of their antennae. These hairs are hollow and contain special receptors called chemosensory neuronswhich sort and send the chemical information to the ant’s brain.
Odors, like those emitted by an ant’s greasy fur, act as chemical ‘keys’..” Ants can smell these odor switches only if they are inserted into the correct set of chemosensory neuron “locks”. The neural lock remains closed to any odors except the specific key. However, when the correct key connects to the correct neural lock, 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 nest neighbors—or fights between unrelated individuals.
A colony of carpenter ants (Camponotus floridanus) reared in the Zwiebel Laboratory at Vanderbilt University. LJ Zwiebel, Vanderbilt University, CC BY-ND
Changing the locks
To better understand how ants detect and transmit information, we use laboratory tools such as precisely targeted drugs and genetic engineering to manipulate their sense of smell. We are particularly interested in what happens when an ant’s sense of smell goes awry.
For example, when we prevent an odor “key” from opening a chemosensory “lock,” this prevents chemical information from reaching the brain. It would be like plugging your nose or standing in a completely dark room – no smells or sights would register. We can also open all the “locks” at the same time, which floods the neurons with too many messages. Both scenarios dramatically compromise the ant’s ability to detect and receive accurate information.
When we messed with ants’ sense of smell—whether by turning off or flooding their smell receptors—we found they no longer attacked out of sync. Instead, they became less aggressive. In the absence of clear information, the ants showed restraint and preferred to accept rather than attack their mates. Put another way, ants ask questions first and shoot later.
We believe that this social constraint is hardwired and gives ants an evolutionary advantage. When living in a colony with tens of thousands of sisters, a simple case of mistaken identity or misunderstanding can lead to deadly infighting and social chaos, potentially very costly.
When the ants in our experiments lose their sense of smell and their ability to detect accurate information is compromised, they no longer stick together in a cohesive colony.
Not only do they fail to recognize and attack enemies, but they also stop cooperating with their friends. With no nurses to care for the young or foragers to gather food, the eggs dry up and the queen goes hungry.
We found that without an accurate means of communicating and receiving chemical information, ant societies disintegrate and the colony quickly dies. Miscommunication or lack of accurate information it affects other highly social animals, including humans, as well. For ants, everything depends on their sense of smell.
Lawrence Zwiebel is a professor of biological sciences and of pharmacology at Vanderbilt University. Stephen Ferguson is a postdoctoral fellow in biological sciences, Vanderbilt University. This article was republished by The conversation under a Creative Commons license. Read on original article.