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Parasites in ant colonies
Parasites in the ant world is very common, but they do not seem to affect their host’s life in a wider sense. One of the more famous parasites is the ”zombie-fungus” that infects its host and makes it climb high above the ground. When reaching the top the ant will hold on until the parasite kills it.
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When discussing ant parasites they might not seem like a good part of the ant-life. But they are important to the ecosystem and contributes as any other to a well-balanced fauna of insects.
A great example where parasites serves as a balancing force is a sort of fly, resembling our regular fruit fly. When the ant species of Pheidole dentala emerges from its nest to defend food supplies from the species of Solenopsis texan, the fly show up and balances out the conflict. They attack the strongest, soldiers of the Pheidole army, and tries to lay their eggs on them. The soldiers, who would usually win the fight, flees the battlefield and let their weaker sisters do the fighting. The flies don’t seem to attack any of the smaller workers of any species, which eventually results in the Solenopsis standing as victors. One interesting thing about this is the timing. The flies are not active during early spring and late autumn, which flips the odds in Pheidole’s favour – giving them free roam during this period. This way the flies servers as weighers in the conflict, making sure the two species can live side by side and not exterminate the other. (1) This was first observed in Texas, but has since been seen in many forests of the world.
Deadly Ant Parasites in the Ant Colony
Individual ants can be targeted by parasites. For example, nematodes (or roundworms) have been found in the abdomen of several different ant species. And during summer days, flocks of flies have been seen flying above ant hills. These do not differ very much from the above mentioned fly, and have the same goal: to lay eggs on the ants. The eggs are put in the back of the neck, eventually killing the ant as the larvae digs its way through the head and body.
Other parasitic flies are the phorid flies (Pseudacteon). They sneak up on ants outside of their nests or on their roads, and when within reach they lash out and plants an egg in the ant’s abdomen. Other flies take advantage of the nuptial flights and lay their eggs in newly mated queens. This stops her from laying her own eggs and will make her, without her knowing it, take care of the flies larvae and pupae. The queen will later die, letting the fly grow into adulthood without her meddling. (2)
Ant Parasites: Fungi
When looking upon the topic of ant parasites, fungi quickly reveals itself as a popular subject. Their ways are vastly different from each other, but many of them have one thing in common: the killing of the host ant. One of them comes from the Cordycep family. It infects an ant and starts growing within its body. Eventually it will push itself out in the form of a sprout (usually somewhere in between the major body segments. Cordycep subdiscoidea in particular sprouts from the neck of the ant, or right behind the head, and can grow up to 10 centimeters tall. The ant will die in a ”living” position, making it look alive – apart from the infestation of fungi on its body, head and mouth.
Other fungi arn’t as nasty. They neither kill nor harm their host ants. Some of them situates themselves on the outside of the ant’s body while others spreads through their mouths, making the spread of the fungi throughout the colony easy.
Despite the fungi’s success of infesting and spreading through ants, the ant colonies themselves do not seem to be much threatened by them. The fungi are thinly spread and do not affect the demography of the ant world in particular. The scientist Wheeler wondered about the phenomena and guessed that the reason for this is the high level of sanitary care the ants tend to have. They tend to themselves and other ants all the time, thereby repelling ant parasites though antibiotic secretion they exude from their glands. (3)
1. Bert Holldobler & Edward O. Wilson (1990) “The Ants” p. 434
2. Per Douwes, Johan Abenius, Björn Cederberg, Urban Wahlstedt (2012) Nationalnyckeln “Steklar: Myror-getingar. Hymenoptera: Formicidae-Vespidae” p. 46 (Swedish)
3. Bert Holldobler & Edward O. Wilson (1990) “The Ants” p. 557