20 June 2013

Black Swallowtail (Papilio polyxenes) caterpillar. Updated with egg and first instar.

Remember the golden spherical Black Swallowtail egg I posted on the June 8 linkdump?  In due time it hatched and the little fellow has been happily munching away on some bronze fennel and Queen Anne's Lace.  He's living on our screen porch protected from parasitic wasps, so I should be able to document the full life cycle for the blog.

You can click to embiggify, but the image is not quite sharp because when I took this photo a couple days ago I used a long lens to isolate him against a blurred background, and thus didn't get quite enough depth of field to get all of his spectacular body features in focus.

And meanwhile -

-  I spotted another BST hovering over the rue we have planted by the mailbox.  She was oblivious to my approach, intent on ovipositing.  Frankly, if I had not seen her zoom in on this particular inflorescence of the rue, I would never have been able to spot the fiendishly-well-camouflaged greenish-yellow egg on the stamen of the greenish-yellow flowers.

Addendum:  On the sixth day after the above photo was taken, the egg now appears dark:

When I zoom in maximally, I believe I can see three black stripes inside the greyish-black egg, suggesting that it's about ready to hatch.

Update:  Just 3-4 hours after the photo above I looked again, and the first instar had emerged:

I'm always amazed how much bigger first instars look than the eggs they come out of; they must be tremendously compressed in there, or perhaps the new caterpillar is mostly air on the inside.

It probably ate the egg capsule for its first meal; I hope it will be satisfied with the stamen or pollen or a petal for the next day or two, because it's so small I'm reluctant to try to transfer it to a fresher rue blossom on a stem with leaves.  (The annonyingly inappropriate black filament is probably a cat hair; they like to explore the work table).


  1. Click to embiggify?? Love it, Stan, love it!

  2. Me too, I shall have to use embiggify today. lol. You are a good butterfly Dad!

  3. Thanks to you I have been looking for butterfly eggs everytime I go for a walk. I figuerd it would be cool to show my daughter how a caterpillar changes to butterflies. I just cant seem to locate any eggs. Perhaps I do not have a keen eye like you to spot them. Ty for the post. keep it up.

    1. It's very challenging to find eggs (the butterflies have had several millenia of experience in hiding them). The easiest to find are Monarch eggs on the underside of milkweed leaves (use the search box in the right sidebar to find some relevant old posts). Another easy one is to plant a cabbage or broccoli in your yard and wait. It's almost invariable that a Cabbage White will find the plant and lay eggs on it.

      Other than that the best way is to observe a butterfly in the act of ovipositing. One key is that instead of fluttering around the flowers to get nectar, they land on the leaves; and if you watch you can see the abdomen curling down to glue the eggs on to the plant.

  4. Perfect! Thank you for the tip. I searched for monarch eggs on milkweed, & just realized those little green "things" I though were galls, are the actual eggs!

    1. Excellent. Here's what to expect next:



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