An ant that protects herself with… um… butt foam

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I’ve left you hanging long enough. Here is what Thursday’s mystery ant, an Asian Pachycondyla, does when bothered. She sprays foam from her venom gland.

Pachycondyla defensive foam takes two forms: stringy and clumpy. This ant demonstrates both.

This big tropical ant is a new addition to Andy Suarez’s University of Illinois research bestiary. A colony was collected by the recent multi-institutional Cambodian expedition for studies of ant venom chemistry, among other projects. A 1981 paper by Maschwitz et al describes the unusual defensive behavior:

When disturbed, two species of Malayan Pachycondyla release foam threads more than 10 cm in length or foam piles. The source of the proteinaceous foam is the enlarged venom gland, which is probably frothed up by air from the spiracles of the spiracular plates. The Dufour’s gland normally producing hydrocarbons in stinging ants is atrophied. Therefore, absence of the Dufour’s gland could be essential to the foaming ability, since the lipophilic hydrocarbons inhibit froth production in protein solutions. The release of foam is a mechanically acting defense mechanism, which is very effective against small mass-attacking ants. Pachycondyla species are also able to sting effectively.

I can vouch for their ability to sting effectively, too*.

When I don't let go*, the ant broadcasts more foam.
The froth is ejected so rapidly it gives the impression of silly string.
Close-up of the anal opening in bubble-blowing action.
Not done yet.
The sheer quantity of foam produced in only a few seconds is astounding.

*no ants were harmed in the making of this post, and the colony was rewarded for their participation with several fat crickets. I, on the other hand, discovered that the ants have a more conventional defense, too: a good, old-fashioned stinger.


source: Maschwitz U, Jessen K, Maschwitz E (1981) Foaming in Pachycondyla: a new defense mechanism in ants. Behav Ecol. Sociobiol 9:79-81.

17 thoughts on “An ant that protects herself with… um… butt foam”

  1. Alan N. AntsMania

    It’s totaly amazing! This behavior has been observed to hunt insect? Or is it only deployed for defense?

  2. This is now my favorite blog post of the day… in part because of the title. I secretly have the sense of humor of a twelve-year-old boy. Great photos, as always!

  3. James C Trager

    Butt foam? Anal opening? Produced in the venom gland and appearing to emerge from the sting in picture #4. Still, a great title!

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  5. Henry (Rob) Robison

    Now I have heard everything…..butt foam from an ant! My Ph.D. in zoology never mentioned “butt foam” from ants! How did I miss this? Time to return to school! Loved your photos Alex and the post, as always.

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