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Thursday, June 28, 2018

Don't put on deodorAnt: How smelly ants communicate

When humans communicate, we usually use words and body language like hand gestures. This helps us work together and make complex group decisions like where to eat, how to win a competition, or how to throw a surprise party. Ant colonies, which often contain hundreds or thousands of individuals, also need to make complex collective decisions. From choosing where to live to finding the next meal, ants constantly need to relay information to each other to keep the colony running smoothly. Compared to humans however, ants are nearly blind and deaf. How then, do they communicate with each other?
Scientists have shown that ants’ main mode of communication is through “smelling” chemical signals called pheromones. While the existence of human pheromones is still being debated, pheromones are used by many animals and insects to communicate with members of their own species. In ants, pheromone use is varied and complex. If you’ve ever observed a trail of ants on the ground, you may have also noticed that they often touch antennae. According to a recent study, antennae can serve as both receptors and sources of information. A type of pheromone called cuticular hydrocarbons (CHCs) on the antennae is unique to each colony and helps members within a colony recognize each other. When researchers cut off the antennae from an ant, ants from other colonies were unable to identify her as someone from an opposing colony.


Oecophylla longinoda workers touch antennae to “smell” each other’s pheromones to determine if they are friend or foe [1]

Apart from CHCs on the antennae, ants can secrete pheromones from many other different places, including glands on their feet, their abdomen, or their thorax. Using combinations of different types of pheromones, ants are able to relay a variety of messages. In some species, individuals secrete a danger pheromone when they die to warn other colony members. In others, larvae that are destined to develop into queens can secrete a “princess pheromone” to ensure that they receive extra care.
Perhaps the most documented use of ant pheromones is trail pheromones that lead to food sources. Since finding and gathering food is energy-intensive and time-consuming but crucial to their survival, many species have evolved a sophisticated set of pheromones to help them in the process. For example, Pharoah’s ants (Monomorium pharaonis) use non-volatile pheromones to organize and remember the trails that are being, or have been, explored. Once they’ve discovered a food source, they use more volatile pheromones to quickly recruit nearby ants. If a trail is non-rewarding, they can also secrete repellent pheromones to prevent other ants from wasting their energy exploring the same trail. Even for ants with less complicated systems, simple pheromones can effectively help them scavenge for food. As more ants go down a rewarding trail, more pheromones are secreted, causing a positive feedback loop that recruits even more ants to a food source. In a similar way, as fewer ants go down a non-rewarding trail, pheromones on the trail eventually dissipate, preventing more ants from going down the same trail. This allows foraging ants to make complex decisions about where to eat and how to feed thousands others in their own colony.
A trail of Odorous House Ants (Tapinoma sessile) [2]

While pheromones have a crucial role in ant communication, ants also use other non-chemical methods of interacting with each other. Some ant species use tandem running instead of pheromone trails to lead other members to food sources. Tandem running is a tactile approach that often starts out with an ant going up to another ant and tapping the other ant very quickly with her antennae, sometimes also touching the other ant with her forelegs. Once the other ant realizes that something is happening, she will follow the first ant and start a very slow game of tag, occasionally touching her to indicate that she is close behind.



Tandem running recruitment [3]


Another tactile mode of communication involves trophallaxis, a process in which two ants exchange regurgitated liquids, essentially throwing up in each other’s mouths. One ant can urge another ant to regurgitate by lightly and repeatedly tapping her lower mouth plate. This method is so efficient that social parasites like Myrmecophilous staphylinid beetles have mimicked it to force ants to feed them regurgitated food.
Trophallaxis between a soldier and a worker of the turtle ant Cephalotes pusillus [4]

Even though ants are nearly deaf to airborne vibrations--what humans perceive as sound--they are very sensitive to vibrations that are carried through substrates. Thus, ants can acoustically “talk” to each other by producing vibrations in two main ways: by drumming directly against a substrate or by rubbing specialized body parts together--a process called stridulation. Ants that live in wooden or carton nests are more likely to use drumming because these substrates are better at carrying vibrations throughout a colony. In species like Camponotus senex, an ant can quickly start an alarm signal by drumming against the nest. As other ants sense the drumming, they also follow suit, producing sounds that are even louder than human speech. This system allows ants to make collective decisions for defending themselves or for evacuating dangerous areas.

 By combining all these types of communication--chemical, tactile, and acoustic--ants are thus able to make complex decisions and work along with thousands of others in their colony, a feat that would be impressive in any society.

 Further Reading

 Jackson, D. E., & Ratnieks, F. L. (2006). Communication in ants. Current biology, 16(15), R570-R574. https://doi.org/10.1016/j.cub.2006.07.015

 Holldobler, B., & Wilson, E. O. (1990) The Ants. Harvard University Press. http://www.antwiki.org/wiki/The_Ants_Chapter_7

 Antkeepers. (2018). How Ants Communicate. Antkeepers. https://www.antkeepers.com/facts/ants/communication/
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