Why Are Army Ant Queens So Odd?

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Consider the gargantuan insect at the heart of this BBC clip, an African Dorylus queen:

She’s a strange beast. All army ant queens are.

Neivamyrmex opacithorax, queen (Arizona, USA)

Let’s contrast these insects with a queen whose robust form is representative of most other ant species:

Proatta queen & worker

Most army ant queens are long and slender, their thorax reduced, and they, like their workers, are either blind or nearly so. Technically, they are dichthadiigyne.

Why?

Army ant queens have two particularly stressful- and diametrically opposite- behaviors. First, they lay eggs. All the eggs. As army ant colonies can be huge (a few tens of thousands to 20 million or so individuals), and since workers don’t live long, queens pump out eggs at an enormous rate. Up to tens of thousands per day when they are in their laying cycle. Consequently, their abdomens must be large accommodate an extensive system of ovaries.

Second, queens have to be able to run in the frequent colony migrations. So they can’t merely be soft ginormous laying machines. They’ve got to be strong and streamlined, with tough walking legs. And unlike most ants whose queens fly to disperse, army ant queens have lost the flight apparatus and redesigned their thorax for dispersal by foot.

Thus, army ant queens are the product of a selective environment pulling in two directions at once: towards bloated egglayer, and towards distance runner. The result is a strangely armored wormy thing.

Aenictus congolensis, from Wheeler (1930): Philippine ants of the genus Aenictus with descriptions of the females of two species. J. New York Ent Soc 38: 193-212.

9 thoughts on “Why Are Army Ant Queens So Odd?”

    1. I’ve got a post in the works on some adult workers I photographed feeding in the field. I don’t think it answers the questions about how soldiers & queens feed, though it might provide a clue or too.

  1. Norma Holly Eslick

    The queens are fed by the workers through a process called tropholaxis — mouth to mouth passing of food. Adult ants can feed only on liquids (plant juices, body fluids) because their digestive tract is narrowed by the tiny “wasp waist” that separates the thorax from the abdomen. After feeding themselves, workers can take in additional fluid and save it in the crop, a second stomach which is used to store food. Solid foods are torn into small pieces and taken to the nest for the larvae who are basically made up of mouthparts and a stomach, so to speak.

    Most ants are omnivores – they feed on plants as well as meat, which usually consists of dead insects. But army ants are carnivores: they feed only on live or freshly killed prey. They suck the body fluids out of prey carcasses and then tear them into smaller pieces. These are carried back to the nest to be crushed into a mushy paste and fed to the larvae.

    Hope this helps,
    Norma

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