Munching the dill

I haven’t seen many butterflies this summer, but they have obviously visited the backyard garden.  Yesterday when I went out to collect some dill for pickle-making, I found these Black Swallowtail caterpillars munching my dill plants.

A female Black Swallowtail must have visited here a couple of weeks ago, because these are almost fully grown fifth instar (last molt) larvae that will soon crawl away to pupate.

A female Black Swallowtail must have visited here a couple of weeks ago, because these are almost fully grown larvae that will soon crawl away to pupate.

I watched while these two devoured stem after stem of the dill, eating their way from the ends of the delicate leaves down to the woody part of the stem.  Every now and then, they stopped to eject a little square packet of excreta.

This one is starting off at the tip of one branch that still has a few leaves.

This one is starting off at the tip of one branch that still has a few leaves.

swallowtail caterpillar

The mouth parts don't look all that massive, but they make short work of this stem.

The mouth parts don’t look all that massive, but they make short work of this stem.

The first three pairs of appendages (thoracic area) will develop into the true legs of the adult.  The fleshy pads in the abdominal region  are stumpy projections that have suction cups to assist locomotion.

The first three pairs of appendages (thoracic area) will develop into the true legs of the adult. The fleshy pads in the abdominal region are stumpy projections that have suction cups to assist locomotion.

Black Swallowtail caterpillars exhibit a variety of color phases during development, as shown in these wonderful photos by Bob Moul.

The first two instars are black, gradually developing spots.  The last instar is black and yellow, gradually becoming greener as it gets larger.  Unlike the Monarch chrysalis, the Black Swallowtail pupa is supported by a silken thread wound around its middle, as well as at the tip of the former abdomen.   The male and female are distinctly different in the markings on their hind wings.

The first two instars are black with a white band around the middle, gradually developing spots. The last instar is black and yellow, gradually becoming greener as it gets larger. Unlike the Monarch chrysalis, the Black Swallowtail pupa is supported by a silken thread wound around its middle, as well as at the tip of the former abdomen. The male and female are distinctly different in the markings on their hind wings.

Black Swallowtails prefer to lay their eggs on plants in the carrot family, especially dill, Queen Anne’s lace, fennel, parsley.  This first generation of butterflies will mate and lay eggs, but then those larvae (second generation) will pupate over the winter, finally emerging when it becomes warm enough again the following summer to complete their metamorphosis and start the life cycle all over again.  This means that the two generations of caterpillars have different programming for development, some completing their metamorphosis quickly within two weeks, but others entering a dormant phase that can last for months.  Interesting control mechanisms at work here.

12 thoughts on “Munching the dill

  1. I haven’t seen any of our Swallowtails (Papilio machaon) yet I had some on the fennel last year and the caterpillars are very similar to your Black Swallowtail caterpillars. I never knew that caterpillars could reproduce is this an unusual case?

    • Sorry, that was very bad editing above. It should have said when the first generation of caterpillars metamorphoses, the butterflies mate, etc. No caterpillars have mature reproductive organs that I know of.

    • I am surprised there is only one caterpillar in the fennel. I actually had two large and six small ones in just two short rows of dill plants. Perhaps a few more will show up later. Thanks for commenting!

  2. Pingback: Munching the dill | Skipping Stars Productions LLC

    • Yes, brightly colored, but not poisonous or distasteful, like the Monarch caterpillars. Maybe, these caterpillars are just mimicking a warning coloration to make predators think they are distasteful?

  3. Beautiful close-up shots of the caterpillars, Sue. I don’t think that I have ever looked that closely at a caterpillar’s mouth. The info that you provided was fascinating too. Metamorphosis is an amazing process. I was not aware that a caterpillar went through so many developmental stages.

    • Did you also notice they seem to have no eyes, or just very small simple eyes. So, all that sophisticated compound eye development must take place during the pupal stage as they metamorphose into adults. Amazing!

  4. Pingback: A different look — for a good reason | Back Yard Biology

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