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Black Swallowtail Larvae Defending Themselves

7-8-19 black swallowtail larva 0U1A0103Caterpillars, the larval stage of moths and butterflies, are very susceptible to predators (escaping quickly is not an option). Much of their energy in this stage is devoted to defense mechanisms to thwart would-be predators. A partial list of these defenses includes irritating bristles with detachable tips (Tussock Moths), toxic “breath” (Tobacco Hornworms, consumers of tomato plants, tobacco and other plants in the nightshade family, release toxic, bad-smelling nicotine), toxic bodies (Monarchs) and anti-coagulant venom (Giant Silkworm Moths).

Black Swallowtail (Papilio polyxenes) larvae defense mechanism strategies change as they develop. In early stages, or instars, they mimic bird droppings (not an appealing meal for most predators) and older larvae possess bright yellow-orange, horn-like organs behind the head known as osmeteria (see photo inset). When threatened, larvae rear up, extrude the osmeterium, and attempt to smear potential predators with a chemical repellent.

Black Swallowtail larvae are frequently sought after by parasitoids, which can locate their hosts by chemicals in the hosts’ feces (frass). To decrease their chances of being parasitized, Black Swallowtail larvae toss their fecal pellets away from themselves with their mandibles.

To learn much more about both moth and butterfly larvae, go to

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6 responses

  1. Fantastic photos!

    July 8, 2019 at 9:13 am

  2. Alice Pratt

    Awesome photos! You know how much I love BST caterpillars. Haven’t seen any, yet, in the ‘yarden,’ there’s plenty of parsley, rue & dill for them to munch on.

    July 8, 2019 at 11:45 am

  3. Alice Pratt

    I’ve left 2 comments, they aren’t visible, this happened on Eliza’s blog, yesterday.

    July 8, 2019 at 1:26 pm

    • Sorry, Alice. I’m afraid one disadvantage of WordPress is that I have no control whatsoever on that end.

      July 8, 2019 at 3:34 pm

  4. Interesting!

    July 8, 2019 at 7:54 pm

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