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.
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.