ARMY ANT

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Here I am on another plane, writing blog posts when I should really be planning how I’m going to be spending my next few days in primatology nirvana. We’re on our way to Chicago for the joint meeting of the International Primatological Society and American Society of Primatologists (ooh err), the program is 82 pages long, and I want to go to every talk which is physically not possible. So, in order to shirk the responsibility for a little longer, let us travel back to the rainforest for the last of this round of Payamino posts.

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Army ants were one of those species which, like the bullet ants, I was both excited and alarmed to see. For the uninitiated, they are a type of ant that are renown for their hunting raids, which involve hundreds of thousands of individuals swarming over an area and eating everything in their path- grasshoppers, scorpions, tarantulas, lizards, you name it (there’s some cool videos here showing them at work). Because they wreak such havoc on the areas which they raid they are also nomadic- moving from site to site every 20 days or so, and making camps in bivouacs that are made from the living bodies of the ants themselves. The figures for single colonies are insane- the raiding columns can be over 100m long, and they can capture and kill over 30,000 prey items in a single day. Even though its the smaller castes of ant that do the voracious hunting, the soldiers (also known as majors) have some of the most intimidating mandibles in the animal kingdom. Everything about army ants says the same thing: don’t mess. They are one of the icons of the jungles of South America, and I was apprehensively hoping to see some in action.

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By far, the largest bivouacs I saw on the move were up in the montane rainforests of Sumaco National Park- the largest were 2m thick. These photos however were taken just behind the research station in moist lowland forest, when for a couple of days we were lucky enough to have a colony passing over the path that led from the station to the trails leading to deeper jungle. There isn’t many I’m afraid, but in my defence I was trying to catch individuals that were constantly on the move (which is why almost every photo here of soldier ants, which stood relatively still standing guard compared to the frenetic workers) while at the same time making sure I was maintaining enough distance not to be worthy of their notice (I think the size of those mandibles explains why). Even though they were essentially just moving from A to B, there were tonnes of different behaviours going on. When these guys move, they move everything– even the pupae, which were carefully being ferried from one location to the next by the workers. Ocassionally a piece of their latest victim would also make its way across the path- a grasshopper leg here, a caterpillar there. Individuals were constantly going up to each other and stroking together their antennae (I presume to read pheromones), which would either result in a amicable parting or start a tussle.

Something like 300 other species are known to be dependent in some way or another on the activities of these ants, from birds that follow the swarms as they hunt, to wasps that parasitise the larvae, to beetles that live incognito within the bivouacs themselves. There is still so much we don’t know about them, but it’s clear that they are an endlessly fascinating cornerstone of the forest ecosystem. In my opinion, one of the biological wonders of the world.

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NB. I got my army ant facts and figures from this wonderful article by Rettenmeyer et al. Sadly it’s paywalled, but well worth a read if you have journal access. I could have happily quoted the whole thing.

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