The Amazing Physics of Fire Ants
14 July 2018
This brown material looks like blob but it's very much alive. It's made of Fire Ants.
And those, are not the hands of a vet or a zoologist. Those are the hands of an engineer. We are in an engineering school. More precisely, at the Georgia Institute of Technology.
What makes Fire Ants interesting to engineers? Fire Ants can build... with their bodies. They are animals, but act like a material that you can test like a gel or fabric.
They have incredible strength, and move very cohesively as a group.
They have learnt to do that because where they come from, South America, the rainy season inundates their underground homes. By linking together, placing their eggs and queen on top, they have more chances to save the colony, and their genes to be passed on. And because evolution IS ALWAYS by natural selection, after thousands of years, those ants not capable of floating and not really hydrophobic, died off, leaving us these strong kickass ants engineers are so into today.
Groups of fire ants are able to flow through a funnel like a thick, syrupy liquid. They are also able to be pressed down and rebound like a rubbery solid.
A colony is considered fluid and solid from the way they react to different pressure situations and researchers are studying them for science.
On a similar note humans also have a tendency to behave like fluid when densely packed... like Japanese people in a train vagon during rush hour LOL Pedestrians walking down a sidewalk in opposite directions usually manage not to bump into each other.
Any single ant has a certain amount of hydrophobia -- the ability to repel water -- and this property is intensified when they link together, weaving their bodies much like a waterproof fabric.
The ant-raft is "self-healing": it's robust enough that if it loses an ant here and there, the overall structure can stay stable and intact.
In short, the ant raft is a super-organism and the ants become a kind of granular medium. Even weirder, when they all link up like that, the ants start exhibiting more fluid-like properties -- so much so, that it's possible to "pour" them from a teapot into a teacup.
To study them, the Georgia Institute has done all sort of experiments. They fed ants iodine, which is radioactive, froze them with liquid nitrogen and even coated them in Gold.
Thank god Dogs cannto do that... this video could have caused an uproar.
All these experiments to create mathematical models to describe the ants behaviour. And they characterized the ant ball as a "viscoelastic material", which means they have properties of both a fluid and a solid.
You can squish the ant ball, and it will give back the energy.
Studying how ants move within their group could help the field of robotics by allowing small pieces to self-assemble into larger structures. Because a disturbed group of ants can also quickly return to their position, they could also influence the next generation of self-healing materials.
Ants communicate with each other using pheromones, sounds, and touch. The use of pheromones as chemical signals is more developed in ants, such as the red harvester ant, than in other hymenopteran groups. Like other insects, ants perceive smells with their long, thin, and mobile antennae.
The paired antennae provide information about the direction and intensity of scents. Since most ants live on the ground, they use the soil surface to leave pheromone trails that may be followed by other ants. In species that forage in groups, a forager that finds food marks a trail on the way back to the colony; this trail is followed by other ants, these ants then reinforce the trail when they head back with food to the colony. When the food source is exhausted, no new trails are marked by returning ants and the scent slowly dissipates.
Camponotus sericeus on Vachellia seyal , Senegal
This behaviour helps ants deal with changes in their environment. For instance, when an established path to a food source is blocked by an obstacle, the foragers leave the path to explore new routes. If an ant is successful, it leaves a new trail marking the shortest route on its return. Successful trails are followed by more ants, reinforcing better routes and gradually identifying the best path.
Ants use pheromones for more than just making trails. A crushed ant emits an alarm pheromone that sends nearby ants into an attack frenzy and attracts more ants from farther away. Several ant species even use "propaganda pheromones" to confuse enemy ants and make them fight among themselves.
Pheromones are produced by a wide range of structures including Dufour's glands, poison glands and glands on the hindgut, pygidium, rectum, sternum, and hind tibia.
Pheromones also are exchanged, mixed with food, and passed by trophallaxis, transferring information within the colony. This allows other ants to detect what task group (e.g., foraging or nest maintenance) other colony members belong to.
In ant species with queen castes, when the dominant queen stops producing a specific pheromone, workers begin to raise new queens in the colony.
Some ants produce sounds by stridulation, using the gaster segments and their mandibles. Sounds may be used to communicate with colony members or with other species.
Many animals can learn behaviours by imitation, but ants may be the only group apart from mammals where interactive teaching has been observed. A knowledgeable forager of Temnothorax albipennis will lead a naive nest-mate to newly discovered food by the process of tandem running. The follower obtains knowledge through its leading tutor. The leader is acutely sensitive to the progress of the follower and slows down when the follower lags and speeds up when the follower gets too close.
Controlled experiments with colonies of Cerapachys biroi suggest that an individual may choose nest roles based on her previous experience. An entire generation of identical workers was divided into two groups whose outcome in food foraging was controlled. One group was continually rewarded with prey, while it was made certain that the other failed. As a result, members of the successful group intensified their foraging attempts while the unsuccessful group ventured out fewer and fewer times. A month later, the successful foragers continued in their role while the others had moved to specialise in brood care.
Cooperation and competition
Not all ants have the same kind of societies. The Australian bulldog ants are among the biggest and most basal of ants. Like virtually all ants, they are eusocial, but their social behaviour is poorly developed compared to other species. Each individual hunts alone, using her large eyes instead of chemical senses to find prey.
Some species (such as Tetramorium caespitum) attack and take over neighbouring ant colonies. Others are less expansionist, but just as aggressive; they invade colonies to steal eggs or larvae, which they either eat or raise as workers or slaves. Extreme specialists among these slave-raiding ants, such as the Amazon ants, are incapable of feeding themselves and need captured workers to survive.
Meat-eater ants (Iridomyrmex purpureus) working cooperatively to devour a cicada (possibly Psaltoda moerens but damage to the victim makes a definite identification difficult to confirm). The cicada is approximately 60-70mm long, the ants are approximately 15mm long. East Gippsland, Victoria, Australia, 11 Nov, 2009.
Captured workers of the enslaved species Temnothorax have evolved a counter strategy, destroying just the female pupae of the slave-making Protomognathus americanus, but sparing the males (who don't take part in slave-raiding as adults).
Ants identify kin and nestmates through their scent, which comes from hydrocarbon-laced secretions that coat their exoskeletons. If an ant is separated from its original colony, it will eventually lose the colony scent. Any ant that enters a colony without a matching scent will be attacked.
Also, the reason why two separate colonies of ants will attack each other even if they are of the same species is because the genes responsible for pheromone production are different between them. The Argentine ant, however, does not have this characteristic, due to lack of genetic diversity, and has become a global pest because of it.
Parasitic ant species enter the colonies of host ants and establish themselves as social parasites; species such as Strumigenys xenos are entirely parasitic and do not have workers, but instead, rely on the food gathered by their Strumigenys perplexa hosts.
This form of parasitism is seen across many ant genera, but the parasitic ant is usually a species that is closely related to its host. A variety of methods are employed to enter the nest of the host ant. A parasitic queen may enter the host nest before the first brood has hatched, establishing herself prior to development of a colony scent. Other species use pheromones to confuse the host ants or to trick them into carrying the parasitic queen into the nest. Some simply fight their way into the nest.
A conflict between the sexes of a species is seen in some species of ants with these reproducers apparently competing to produce offspring that are as closely related to them as possible. The most extreme form involves the production of clonal offspring. An extreme of sexual conflict is seen in Wasmannia auropunctata, where the queens produce diploid daughters by thelytokous parthenogenesis and males produce clones by a process whereby a diploid egg loses its maternal contribution to produce haploid males who are clones of the father.
|Written by: Linda Wallers|