update on the yellow bear caterpillar

As some of you will remember, back on July 9th, I wrote:

Yesterday, I collected the caterpillar below — what is, in all probability, a Virginian Tiger moth (Spilosoma virginica), often referred to as a Yellow Bear caterpillar. It was found on the tall Sweet Clover plant (Melilotus alba), which is often seen growing along roadsides. I collected a few sprigs to put in the caterpillar’s new home. I’ve recorded the date that the caterpillar was collected, and I’ll try to record the date that it cocoons.

Well, I didn’t have to wait long. The caterpillar that I collected on July 8th (see above – click on all images for a larger view), had cocooned by July 10th. I’ve often found that caterpillars will cocoon soon after they are collected and placed in a container with their food plants. I don’t know if this is really a response to being moved – almost a form of rebellion to being confined – or if it is just coincidental and more related to their life stage when I happen to find them. I believe it’s actually the latter as large final instar caterpillars are generally the most conspicuous, both in size and in the damage that they do to plants while feeding. In all probability, the caterpillars would have pupated within a day or two even if I hadn’t seen and collected them.

The cocoon of the Virginian Tiger Moth (see above) consists of a dark, glossy-shelled pupa, surrounded by a sort of capsule made from the remnants of the caterpillar’s setae (the “hair” on the caterpillar’s body). This caterpillar attached its cocoon to the leaves of the still green Sweet Clover, but as I had clipped these from the plant, they wilted and dried. This had no effect on the caterpillar within its cocoon.

Yesterday, I examined the cocoon and thought to myself that the moth should be emerging soon, or else it’s dead – perhaps parasitized by another insect. However, this morning, Don noticed the moth on the living room window. I checked the cocoon, and sure enough, there was an “escape hole” in one end (you can see that in the cocoon photo). So, it took about 16 days for the caterpillar to become transformed into the above moth.

One of the very neat things about moths is that the forewings often conceal beautifully marked hindwings or bodies. That’s certainly the case with this moth as the body is marked with bright yellow and black.

As for the “moth project” mentioned in my previous post, it’s not progressing quite as hoped. I have seen a few caterpillars around, but always at times when I was carrying two cameras and no collection containers. At the moment, the main caterpillar project is raising part of the colony of larvae found on the Buckthorn bushes (mentioned in another recent post). I’ll post an update on them later this week.

By the way, just a reminder that the next Circus of the Spineless invertebrate carnival is coming up in early August on Roger’s Words & Pictures blog. If you have an invertebrate post that you’d like to submit, email a link to Roger by July 30th.

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13 Responses to “update on the yellow bear caterpillar”

  1. John Says:

    Thanks for the images and the education, Bev! Wonderful photos, as always. It’s amazing to me to see such different creatures, the caterpillar and the moth, and know they are essentially one and the same.

  2. kenju Says:

    The photos are absolutely fabulous! Especially the top one.

  3. bev Says:

    John – Thanks! Regardless of how many times I’ve seen caterpillars transformed into moths and butterflies, it still blows me away that these creatures go from a wormlike larvae to a soaring insect in only a few days. I can’t help wondering what the caterpillars think as they go through the process of metamorphosis.

    kenju – Thank you! I liked that top photo too.

  4. Ontario Wanderer Says:

    Nice series and much faster than the months that I saved a cocoon that I found mid-winter.

  5. DougT Says:

    I have also noticed that caterpillars often pupate very quickly after you bring them inside. I think that the reasons you cited are correct. Also, caterpillars are much more likely to be encountered outside when the are in their wandering phase just prior to pupation. You commented above that the experience of watching metamorphosis isn’t diminished by repeated viewings. Between the work I do running the butterfly exhibit, and the work that I do breeding butterflies for conservation, I’ve probably watched the process many thousands of times now. It still doesn’t get old.

  6. robin andrea Says:

    I would have never guessed that that white moth would emerge from that caterpillar. What a stunning transition.

  7. bev Says:

    OW – For my moth project, I decided to collect only caterpillars of moths that have more than one flight per summer. I may change my mind and collect a few to overwinter, but I’m always hesitant to do so as I’m not sure I can provide the right conditions for success.

    Doug – Yes, you’re quite right about that “wandering phase”. I encounter that a lot with the Monarchs — if they escape from their containers, they will travel very far. In late summer, I occasionally find large Sphinx caterpillars that are on the move away from the vegetation where they are normally well hidden. That’s just about the only way I would find them.
    It’s neat that you still find the butterflies interesting after watching so many. The life cycle of these creatures has always seemed both beautiful and mysterious to me.

    robin – It’s quite fascinating to see how each caterpillar will turn out. Sometimes you can find some little characteristic that suggests a connection — other times, they’re nothing at all the same. It can be a bit exciting to see what emerges from a caterpillar or cocoon that you’ve found.

  8. Cathy Says:

    I only did this once with a monarch caterpillar years ago. I’ll never forget watching as that jade gold-rimmed chrysalis grew dark and translucent as the butterfly prepared to emerge. The feeling of awe – remains. It resonates in these wonderful pictures.

  9. bev Says:

    Cathy – I love watching monarch chyrsalids. They are the ultimate in amazing transformations.

  10. Marnie Says:

    I released my first monarch yesterday. I was lucky enough to catch both the pupation and the eclosing on video. My second chrysalis is starting to darken, so maybe tomorrow’s the big day for it. The whole thing has been fascinating and I’m starting to think about taking it more seriously another time, getting a better habitat, etc.

  11. bev Says:

    Marnie – I think that’s how things start out – you do it as an interesting and fun experiment, and next thing you know, you’re a little keener and turning caterpillar rearing into a small research project. The good thing is that we learn something new along the way.

  12. Betsy Davidson Says:

    I’ve collected and released a few Monarch butterflies, however this is my first experience with the white tiger moth or milkweed tussock moth catepillars. It has increased
    amazingly in size, however I have no idea what will happen upon pupation. Any advice out there?

  13. bev Says:

    Betsy – In my area (eastern Ontario, Canada), the Virginian Tiger Moths will pupate and emerge as moths in about 2 weeks. I don’t know when the last flight of them would occur, but I expect we’re getting close to that now. I think Milkweed Tussock caterpillars just have one flight per year (at least up here), and any that pupate now would probably overwinter in their cocoons and emerge in spring. If anyone knows differently, perhaps they’ll post a comment.