Prometheas – third and fourth instars

This is what they looked like a week ago, on 8/31:

This is the third instar; the thoracic tubercules are spiky, but not actually very sharp, and they’re bright yellow.


Most of the time, this happens on a twig, and it’s very difficult to see – I’m lucky that this time, a couple of the caterpillars spun their silk pads on the side of the plastic container, and I could see what was happening!


If you look just in front of the caterpillar’s head, you can see the swirls of silk that it lays on the surface.  It will then hook its feet into this silk, to help it peel out of its skin.


This is the same thing, viewed through the clear plastic. The silk pad covers the whole area that the caterpillar is standing on.


I didn’t see any in the process of changing, but this is what you get afterward – the shed skin is attached to the silk, and the caterpillar has walked out in its fancy new suit.


This is the fourth instar, with bright orange tubercules.  I *love* the smiley face!


The knob at the back is still yellow.


Some of the larvae appear to be skipping the fourth instar, and going directly to the red-knobbed fifth instar skin. There are just enough that I can’t be absolutely certain these aren’t just a little ahead of the others – but they’re not all that much larger.  We’ll see if they change again!



6 replies
  1. Carla
    Carla says:

    Great pictures of the transformation. The later instars are almost surreal – can’t help wondering why the turburcules change from yellow to orange. I didn’t know that they spin some silk to help them moult the old skin. Thanks for the education!

  2. Spinfoolish
    Spinfoolish says:

    I can’t tell you how much I am enjoying this! I don’t know much about silk worms, just what I learn in my master spinning classes from Old’s College, but your website is fascinating!! Watching these little guys evolve has been such a joy! Thank you so much for sharing this!

  3. Sugel
    Sugel says:

    Actias luna fifth instar courtesy of Gregory Synstelien..I frequently get asked What is the easiest Saturniidae species for .beginners to rear? .My response has always been Actias luna. Where there had been a single .one-and-a-half .inch caterpillar on a single leaf in a small jar there are now two.caterpillars one just a bit smaller than the other. I reply that the .single caterpillar has shed its skin..Luna caterpillars are said to be in their first instar stage when.they hatch from the eggs.

  4. Judy
    Judy says:

    Love your blog & your site. Have raised silkworms in my classroom for many years & have many peace cocoons in a bag, but have never processed them. Didn’t realize there were different species of silkworms that ate plants besides mulberries. Raising them has become more difficult since they’ve changed the school year to end before June & out here in San Francisco, the trees often don’t leaf out until late April or May. The kids have been missing the whole process. Will definitely be showing your sites to my kids.

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