There are several ways to preserve caterpillars for study. You can boil them and drop them into a jar of alcohol, you can freeze dry them, or you can inflate them.
The photos in this post are all of inflated caterpillars, in the genus Acronicta, found at the Cornell University Insect Collection (CUIC).
Inflating (or “blowing”) caterpillars is a traditional technique that is no longer taught or commonly used, however it can produce fabulous results. The caterpillar remains dry and can be kept in a drawer along with adults, which makes them easier to study than specimens in alcohol. Their external features are usually well maintained – specimens from the early 1900s don’t look much different from modern specimens.
However they are lacking their internal organs, and the last couple of segments are destroyed in the preparation process. The technique is also quite labor intensive and requires unusual equipment. So how does it work?
I have talked to a few entomologists who have inflated caterpillars, but not since their undergraduate or graduate school days. I have found a few resources which describe the process. Here is a description from the University of Minnesota Agricultural Experiment Station:
Basically you cut a slit into the posterior end of the caterpillar, and using a pencil, roll out the guts (starting at the head end). You must be careful to not destroy the hairs and other features of the exterior. Then you insert a glass tube and inflate the caterpillar, and keep the caterpillar inflated as you heat it in a small make-shift oven. One colleague described using a coffee can over a bunsen burner for this purpose.
Once the caterpillar is dry, the glass tube is removed and the caterpillar can be prepared for pinning. Either a wire or stick can be inserted, or the caterpillar can be glued onto the wire or stick by its prolegs underneath the body.
A box of Acronicta americana adults, caterpillars, and pupae
Late (above) and early (below) instars of Acronicta morula
Another benefit of inflating caterpillars is that the body shapes are extended and not distorted by being kept in a liquid. The important bumps and hair positions are kept as their were in life. However the body may be a bit overextended depending on how well it was squished and inflated.
One reason I particularly enjoy the inflated caterpillars is that they are easy to transport and trade – so there are many European species in collections here in the USA. Caterpillars are not often kept in collections to begin with, so to have these specimens available to me for study is quite exciting.
As you can probably guess, I’m going to set up my very own caterpillar inflating oven as soon as I can! And I’ll have another post soon on even more inflated caterpillars I have found at other collections.
University of Minnesota, 1908. 16th Annual Report of the Agricultural Experiment Station. Bulletin #105. How to Collect and Preserve Insects. Pages 119-146.