Rewilding My Lot

Converting a new developer lot into a nature ecosystem — my journey

Giant Swallowtail Caterpillars Have A “Back Off!” Signal

During one of my regular wanderings of the garden I spotted a Giant Swallowtail (Papilio cresphontes) caterpillar on a Common Rue (Ruta graveolens), which is one of its host plants. Given the size of this caterpillar (nearing pupation, I think), it must have been there a while and I just hadn’t noticed it before.

As I reached down to move a leaf to get a better look, suddenly the caterpillar popped out a bright orange V-shaped structure from its head. Clearly it was startled, and so was I! After a short time (less than a minute), the structure was retracted. According to Texas A&M AgriLife Extension, “When disturbed, [Giant Swallowtail] caterpillars display a pair of horn-like, orange glands (osmeteria) which emit a foul smell.” I didn’t smell anything from the distance I was away from it.

Giant Swallowtail caterpillars have also been called “bird poop” caterpillars because of their shape and coloration, and presumably this helps with disguise from predators. But I had no idea they had alarm signals as well, which was something new for me to learn!

Below are photos of this caterpillar with and without its osmeteria activated, and the first photo of this post is another picture of the activation.

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One response to “Giant Swallowtail Caterpillars Have A “Back Off!” Signal”

  1. Molting Black Swallowtail Caterpillar – Rewilding My Lot Avatar
    Molting Black Swallowtail Caterpillar – Rewilding My Lot

    […] through an overnight rainstorm. The next morning I touched it to see if it was still alive, and got the “back off” signal that I have observed in other Swallowtail caterpillars, so that was encouraging. When I returned a few hours later, it had moved a little on the stem and […]

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About Me

Nature Lover.
Inquisitive Observer.
Student Gardener.

I invite you to join me on my journey to convert my sterile (from a nature point of view) new house lot to a healthy and diverse ecosystem, as I make discoveries, mistakes, and hopefully progress. I am not an expert or professional. The project started in February 2023 and the location is Seguin, Texas, USA.

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