Polyergus breviceps facts for kids
Quick facts for kids Polyergus breviceps |
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Polyergus
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P. breviceps
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| Polyergus breviceps (Emery, 1893)
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The Polyergus breviceps is a special type of ant found only in the United States. It's known as a "slave-making" ant because it depends on other ant species to survive. These other ants are usually from the Formica group, like Formica gnava, Formica occulta, and Formica argentea.
Polyergus ants are called "social parasites." This means they have lost the ability to do many basic tasks for themselves. For example, Polyergus workers don't look for food, feed their young, or even clean their own nests. To live, they raid Formica nests and steal their young ants (called pupae). Once these stolen pupae grow up, they become workers in the Polyergus nest, taking care of everything. This kind of relationship is not super rare in the ant world, but what makes Polyergus special is how a new queen can take over a Formica nest all by herself to start a new colony.
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Ant Raids: How Polyergus Takes Over
Polyergus ants are famous for their "slave raids." These raids start when Polyergus workers leave their mixed nest (where Formica workers are already helping out) to find a new target. They are looking for another Formica nest to raid.
Finding a New Home
When scouts find a good Formica nest, they go back to their own nest. They gather other Polyergus ants, and then they all march out in a raiding line. When they attack a Formica nest, the Polyergus ants release a chemical called formic acid. This acid makes the Formica ants panic and run away. The Polyergus ants then grab the Formica pupae and carry them back to their own nest. These pupae will grow up to be new "slave" workers.
Sometimes, a new Polyergus queen joins these raids. After she mates, she leaves the raiding group and searches for a Formica nest on her own. Scientists like Howard Topoff have studied how these queens take over a colony.
Queen's Clever Takeover
When a Polyergus queen finds a Formica nest, she goes inside. The Formica workers immediately attack her. But the Polyergus queen has a trick! She bites them with her sharp jaws (called mandibles) and releases a special scent (a pheromone) from a gland in her body. This scent actually calms the Formica workers down.
The queen quickly searches for the Formica queen. Once she finds her, the Polyergus queen bites and licks the Formica queen for about 25 minutes. As soon as the Formica queen dies, something amazing happens. The Formica workers stop being aggressive towards the Polyergus queen. Instead, they start to groom her, treating her like she is their own queen!
With the takeover complete, the Polyergus queen now has a new home and a whole group of workers to help her. She then lays her eggs, and the cycle of "slave-making" continues.
How the Queen Tricks the Formica Ants
Almost all slave-making ants, including Polyergus, have special jaws that help them attack other ants. For Polyergus queens, when they first enter a Formica nest, they release that special calming scent. This scent helps them take over the colony by making the Formica workers less aggressive.
Scientists did tests to show how important this scent is. They took the glands from Polyergus queens and made a solution. They dipped other ants (that Formica ants naturally attack) into these solutions. They found that when the ants were dipped in the solution from the Polyergus queen's special gland, the Formica ants attacked them for much less time. This shows that Polyergus queens developed a way to make colony takeovers easier over time.
Scientists also found that the Polyergus queen "tricks" the Formica colony by getting chemicals from the Formica queen while she is killing her. In one test, they killed a Formica queen before the Polyergus queen even touched her. Even though the Formica queen was dead, the Polyergus queen still bit and licked her as if she were alive. After this, the Polyergus queen was accepted by the colony!
Another test showed that if there was no Formica queen present at all, the Polyergus queen had a very hard time taking over the nest. This proves that the Formica queen gives some kind of chemical to the Polyergus queen, even if it's not on purpose. The Polyergus queen only needs to kill one Formica queen to be accepted. If a colony has many queens, the Polyergus queen will slowly find and kill every single one of them, sometimes taking weeks to finish the job.
How Polyergus Ants Evolved
Scientists have studied a lot about how "slave-making" ants like Polyergus came to be. One important observation is that almost all raiding ant species have special jaws that are big or sharp, or both. It makes sense that the very thing that helps an ant be a better raider also makes it depend on others, because it can't use its jaws for regular work anymore.
A scientist named Carlo Emery noticed about 100 years ago that "slave-making" ants usually come from ant groups that are closely related to the ants they enslave. This idea is now known as Emery's Rule. Modern scientists have used genetic tests to show that this rule is mostly true. They found that host and parasite ants are often very similar genetically.
A Theory of Evolution for Polyergus
Any idea about how Polyergus ants evolved needs to explain two things: how they started raiding in groups to capture young, and how their queens learned to start new colonies without help.
Howard Topoff has a good idea that combines three things: queen takeover, learning scents, and fighting over territory. Here are his main points:
- Early Ancestors: Long ago, the ancestors of Polyergus were free-living ants that scavenged for food. They would team up to fight other ants of their own kind over territory.
- First Takeovers: Sometimes, a queen from these early Polyergus ancestors would invade a Formica colony. At first, the queen might have just chased away the Formica queen and workers and taken their young. (Some Formica queens do this today!)
- Evolving Tricks: Over time, the Polyergus queens developed special traits:
* Sharp jaws for killing the Formica queen. * A calming scent that reduces aggression from the Formica workers. * A habit of holding onto the dead Formica queen long enough to absorb her scents.
- Learning Scents: The next step was "olfactory imprinting," which means learning scents. Because Polyergus ants grew up surrounded by both their own kind and Formica ants, they learned to recognize both their scents.
- Raids as Territory Fights: Topoff suggests that the raiding behavior of Polyergus comes from their ancestors' territorial fights. A Polyergus worker, raised by Formica ants, might think that Formica ants are part of its own species. So, when it finds a Formica nest, it starts a "territorial raid" just like its ancestors would have. The captured young ants also learn these scents and become workers in the original nest.
Over a long time, these early Polyergus ants slowly became more dependent on others. Eventually, they lost the ability to take care of themselves completely, becoming the "slave-making" Polyergus ants we see today.
