Caterpillar feet are scary

Today I had my first session learning to use the SEM (scanning electron microscope). It was a blast! I spent the past week preparing some egg and caterpillar samples. I took an Acronicta afflicta specimen, cut it up (because the caterpillar was too large to fit into the scope whole), and came up with a protocol for fixing, drying, and mounting the pieces. I really enjoy the step-by-step precision and organization in the electron microscopy lab. There is something about wearing gloves and pouring things from one vial to another in a fume hood that feels so… science-y.

This round was just for practice, I will be gathering more critical specimens to image throughout the rest of the semester. Here is one of my favorite views, a caterpillar’s proleg, or “fake foot”. These are the fleshy nubs that look like legs on the abdomen of a caterpillar. They have hooks on the bottom to grab onto the substrate. I think this view is rather creepy.

This is a close-up of the texture of the caterpillar’s skin.

And one of my favorite structures to view under the scope, a spiracle. This is how caterpillars perform gas exchange, or breathe. While on most insects the spiracles are less obvious, they are typically big and bold on caterpillars. All those little fuzzy looking structures really increase the surface area for gas exchange to occur.

I am so grateful for my instructors and the advice of fellow grad students so far, and I’m excited to continue learning. I think the trickiest part with imaging caterpillars is going to be figuring out my collection and fixation protocol so that I don’t distort the body shape too much. We did an ethanol series (since they were already in 70%) up to 100%, then a few changes of HMDS. If you have ever dealt with preparing caterpillars or other soft bodied invertebrates for SEM and have any tips to share, I’m all ears! The eggs I imaged were either collapsed and infertile or just the shells after the caterpillars had hatched (air dried for several months), so the images weren’t that great. That will be another trick, figuring out how to preserve fresh eggs so they can be imaged in their usual shape.

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Posted on February 2, 2012, in Acronicta, Acronictinae, Invertebrates, Lepidoptera, Noctuidae, SEM. Bookmark the permalink. 14 Comments.

  1. Wow! The spiracles are really cool.

  2. Reblogged this on michelledevilliersartandstories and commented:
    Essential footware!

  3. Very cool photos…thanks for sharing!

  4. When I prep belostomatid eggs for the SEM, all I do is an alcohol series to 100% EtOH and then critical point dry them. They shrivel a little, but FAR less than they do when you air dry them. What structures are you looking for specifically? I’m very insterested to see what you come up with!

    • I’m not sure what features will end up being the most important characters, so I’d like to preserve as much as I can. I hadn’t planned on keeping the eggs for imaging (that I had collected last summer), so from now on I think I’ll store them in ethanol or glycerol.

  5. Spiracles on caterpillars = spiracles on old Buicks!

  6. Great photos! The prolegs have always been one of my favorite caterpillar parts, but your picture looks like a monster with a scary grin. And the skin reminds me of the bearded dragons I used to have. It’s just too bad you can’t take the pictures in color. That would be spectacular!

  7. I think the HMDS technique was developed for viewing vertebrate tissues and, in any case, it has given me the best results with soft-bodied arthropods. Hit or miss, though, and I’ve never been able to figure out why some specimens came out and others shrivelled.

    You’d probably have better luck using field emission low temperature scanning electron microscopy. I don’t have access to an appropriate machine, but here’s a link to an open access article that gives an overview:

    http://www1.montpellier.inra.fr/CBGP/acarologia/article.php?id=1981

  8. I’ve never had the chance to look at something under an SEM. I’m so jealous, those are great pictures!

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