Answer to the Monday Night Mystery

What was that tentacular crown of wonders?

Oecophylla longinoda, the African weaver ant

Tucker got there first, for all ten points: it was the acidopore of a formicine ant. Júlio Chaul picks up two bonus points for getting the genus: Oecophylla.

Rather than explain the acidopore myself, I’ll point you to Roberto Keller:

It is popular knowledge that ants secrete formic acid. What most people don’t know is that only a well-defined subgroup of species have this capacity. Female ants in the subfamily Formicinae have an acid producing gland that sprays its content through a special opening at the rear end of their abdomens, aptly called the acidopore.

It is a beautiful structure when seen under high magnification. It is not a hole in the ant’s plated skeleton, but rather the ventral last external segment folds upwards into itself like a paper funnel (see the smooth area above the opening). Surrounding the acidopore is an inner rim of pointed hairs and a outer rim of flat cuticular projections.

This structure is probably the best synapomorphy we have in ants. It evolved once and, as far as we know, it was never lost during the diversification of this subgroup. It is easy to see and its presence is unambiguous: you see an ant with an acidopore and you know it belongs to the subfamily Formicinae.

9 thoughts on “Answer to the Monday Night Mystery”

  1. I got one right and didn’t have to look it up or anything. I knew right off. Probably helped that I have been identifying a lot of formicines lately. Hey, I might make some kind of myrmecologist yet.

    Way to go Tucker!

  2. Striking image, makes me wonder; what is contained inside the abdomen, it doesnt look like its taken up by a stomach or fatty tissue… more like an extra-cellular fluid of some sort. Or is the flash so powerfull it simply punches through the tissues?

  3. Jim, I will email an illustration to Alex showing the gaster apex of three Camponotus and two Polyrhachis, on only one is there a visible circular opening. Perhaps he will be kind enough to post it on Myrmecos.

  4. I hope he will and I look forward to seeing that. Thanks for sending. The New World and temperate Eurasian species (my experience) have relatively visible ones. I learned something today!
    James (preferably not Jim)

  5. Any case in that the acidopore has changed in evolutionary time to a new fuction with different compounds being secreted? I know this had happened with the metapleural gland in Crematogaster inflata..

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