A Pogonomyrmex badius queen (left) and worker. Queens across species tend to be larger than workers, and have especially large abdomens. Photo by Alex Wild [1]
One reason the queens of this particular species needs frequent access to the brood is because they drink the brood’s saliva. Ants across many species make sacrifices to feed their queens. Since queens rarely leave the nest, this servility often comes in the form of workers either bringing her whatever they eat or regurgitating their food to feed her. However, sometimes more of a sacrifice is required. Some queens subsist entirely off of brood’s hemolymph, the ants’ equivalent of blood. In this case, the queen will use her mandibles to bite or pierce the abdomen (the back-most segment of the ant’s body) of the brood. She will then drink the hemolymph. Larvae that donate are usually scarred but unharmed from this. By giving up bodily fluids, these workers begin serving the queen before they can even walk.
Stigmatomma oregonensis workers piercing larvae with their mandibles so that they can drink the hemolymph. Photo by Alex Wild [2]
Because queens rely on workers for most things, they need to be able to communicate with and control their workers. Many queens accomplish this with the queen pheromone. All ants excrete pheromones, chemicals whose different odors allow individuals to communicate. The queen pheromone is exclusive to queens, and it attracts workers to queens and motivates them to care for her. Because of this pheromone, workers perform tasks such as bringing brood to the queen and if she is outside, escorting her into the nest. Not all queens use just pheromones. Myrmica schencki queens are able to make a sound to alert workers that they are in distress. In one study, worker ants gathered around a speaker playing the queen’s distress noises and assume a specific “on-guard attendance” posture. Butterfly larvae from the species Maculinea rebeli have picked up this trick. These parasitic larvae are placed into ant colonies by their mothers so that they will get food and protection. Thinking they are queens, the workers pay special attention to the butterfly larvae. If there isn’t enough food to go around, the workers will even kill their own brood and feed it to the butterfly larvae.
Colonies can be monogynous, having just one queen, or polygynous, having multiple queens. Though most ant species are exclusively monogynous, polygynous colonies can have up to millions of queens. Though many species of ants are polygynous, queens don’t always get along. Queens don’t want to lose reproductive power; after all, queens are more related to their daughters than to their nieces born from sister queens. Because of this, many polygynous colonies actually practice oligogyny, where all of the queens stay far away from each other and rarely interact.
Because of the tension and competition that comes from having multiple queens, mature queens tend not to view queen larvae favorably. As such, queens have a measurable impact on the growth of larvae. When a queen is present, workers work faster in collecting and feeding larvae at first, but feed them less as the larvae grow bigger. Thus, the larvae stop growing as much, and become smaller ants. In this way, queens assist in the growth of smaller larvae, but suppress the growth of larger larvae. This suppression of larger larvae happens whether or not there are smaller larvae present. Not only do workers feed the larger larvae less, they even compress the larger larvae with their mandibles, leaving scars. Sometimes the queens themselves engage in this. Myrmica schencki queens, the ones who can make distress calls, have been known to bite and sting the butterfly larvae that pretends to be rival queen larvae.
Harpegnathos saltator workers bite a larvae. This suppresses the larvae’s growth. [3]
In contrast, without a strong queen to direct them, workers value larger larvae that can become new queens. When a queen is old or sick but still fertile, she is still able to boost the feeding of little larvae, but no longer able to hold the larger larvae’s growth in check. In addition, workers themselves start to lay more eggs. When no queen is present, larger larvae are favored. Even if there are enough workers to care for all the larvae, the smaller larvae are still somewhat neglected. Workers are able to make their own decisions, even defying the will of the queen if it means the good of the colony.
Workers tend to prefer one queen, as the amount of brood that can be raised is usually constrained by the number of workers that can care for the brood, not by the number of queens producing brood. Thus, the same number of brood can be raised by one or ten queens. Extra queens are a waste of energy, as they don’t really contribute to the nest. When a colony becomes overstuffed with queens, the workers will either kill off unnecessary queens or the colony will undergo fission, where some queens will split off and a few workers will follow each one to start a new colony. So how do workers choose which queens they prefer? According to kin selection theory, workers ought to prefer queens that they are most closely related to. For example, they should prefer a mother queen to a sister queen, as they will be raising their sisters, not their nieces. Or, if queens in a species mate more than once in a lifetime, workers ought to prefer their full sisters as opposed to half sisters. However, it is unclear whether ants can detect how related they are to other ants. The most important factors in a worker’s decision is how fertile and healthy a queen is, although it can still be a tough decision. It may be safer to stay with an older queen who has shown that she can produce offspring rather than staying with a new one who may not be able to. But, the older queen will most likely die sooner. So how do workers decide?
A Monomorium sydneyense queen with her workers and brood. Photo by Alex Wild [4]
In most colonies, queen larvae are kept far from each other. Each queen larvae has a group of “satellite workers” attending to her. Sometimes, these groups fight. This is not out of aggression, but is more a test of loyalty. By fighting, these workers assess each other’s support of their larvae. This is how workers determine which new queens are the most attractive. Often, the queens that emerge first are found to be the most favored, as they have had the most time to develop their queen pheromone and attract workers to their cause. To survive, queens need to maintain support throughout their lives. An experiment was performed in which the dominant queen was removed from the colony, then given back. If she is first greeted by workers who were affiliated with her, then she will be let back into the colony. However, if the first workers to notice her have no special bond with her, then they will gather around her to separate her from the rest of the colony and then abandon her. Sometimes the reverse happens. If a colony doesn’t have a queen, they may be able to fuse with another colony of the same species. There are rules to this interaction, though. Many colonies will only accept new workers if they haven’t been around their queen for several days.
Though small, ants can have huge, complex colonies and networks. Along with this comes its own set of tensions and politics. Queens seek to establish dominance, or at least accumulate power and followers so that they aren’t exiled or killed. Workers choose a queen to follow and battle to test their loyalty. Queens even direct their workers to starve larvae who have a chance of becoming a fellow queen. Next to these schemes and power plays, our elections seem tame.
Further Reading:
Barbero, F., et al. “Queen Ants Make Distinctive Sounds That Are Mimicked by a Butterfly Social Parasite.” Science, vol. 323, no. 5915, 2009, pp. 782–785., https://science.sciencemag.org/content/323/5915/782.
Brian, M. V., and J. Hibble. “Larval Size and the Influence of the Queen on Growth in Myrmica.” Insectes Sociaux, vol. 10, no. 1, 1963, pp. 71–82., https://link.springer.com/article/10.1007/BF02223523.
Glancey, B. Michael, and Clifford S. Lofgren. “Adoption of Newly-Mated Queens: A Mechanism for Proliferation and Perpetuation of Polygynous Red Imported Fire Ants, Solenopsis Invicta Buren.” The Florida Entomologist, vol. 71, no. 4, Dec. 1988, pp. 581–587., https://www.semanticscholar.org/paper/Adoption-of-Newly-Mated-Queens%3A-A-Mechanism-for-and-Glancey-Lofgren/f3fbc05fb5a813e693cbcbafc2f31427f3df5af1.
Hölldobler, Bert, and Edward O. Wilson. The Ants. Springer-Verlag, 1990.
Media Credits:
[1] Photo by Alex Wild: https://www.alexanderwild.com/Ants/Taxonomic-List-of-Ant-Genera/Pogonomyrmex/i-Lsv4S7q/A
[2] Photo by Alex Wild: https://www.alexanderwild.com/Ants/Taxonomic-List-of-Ant-Genera/Stigmatomma/i-s6WmgLf
[3] Video by clint penick: https://vimeo.com/user1351533
[4] Photo by Alex Wild: https://www.alexanderwild.com/Ants/Regional-Ant-Faunas/Australian-Ants/i-zHmndZK
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