Kind of gross
Caterpillars are much more fun when they’re alive. But since they can’t live forever, and they don’t tend to sit still for very long when you’re counting setae or crochet hooks, they must be preserved as specimens.
Unfortunately, they cannot simple be pinned like adult moths. As you can imagine, their bodies would quickly rot and you would have a tray of smelly goo.
The most popular method is to quickly boil them alive until they stiffen, and drop them into a vial of 70% or 95% (if you want to preserve DNA) ethanol. This process is somewhat traumatizing when you have raised a caterpillar from an egg, but there are plenty of ways to rationalize the act of betrayal.
“You will be helping science!”
“Don’t worry, I still love you.”
“I realize you have a nervous system, but it’s debatable whether you feel pain.”
“Oh, I know those thrashing motions and vomit were innate responses. Of course it doesn’t look like you’re screaming, that would be silly.”
Their colors quickly fade once in the ethanol, which is sad considering how vibrant many caterpillars are in life.
Here is a bag of caterpillars I recently loaned to work with:
Now, these guys were not terribly exciting when they were alive, but they had many more shades of brown. If you look closely there is a lot of… stuff… floating around the vials along with the caterpillars. Might be gut contents, bits of the caterpillar falling apart… who knows!
And now I must excuse myself to place a few of these into a dish, creating a sort of caterpillar stew, to examine them under the scope.