Category Archives: Noctuidae
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.
Ok, I lied a little bit. Sometimes caterpillars come out in the winter.
If you live in the US or Canada and see a fat brown caterpillar sauntering across the snow, it is probably Noctua pronuba, the Large Yellow-Winged Dart. It is an introduced species from Europe which has spread across much of North America. The caterpillars feed on all sorts of grasses and forbs, so they can be found just about anywhere (and if you find one, you can feed it just about anything). When we rear these caterpillars in the lab, we simply step outside the building and grab a handful of grass.
Why these caterpillars frolic in the snow remains a mystery. Many species in the same subfamily (Noctuinae) overwinter as larvae, and emerge to feed on warm days in early spring. However this species takes it a step farther, crawling and foraging on bitter cold days when no sensible caterpillar would be out and about. While most caterpillars wait until April or May to emerge, this species can be seen as early as January! Sometimes they even emerge en masse, hundreds of caterpillars wriggling on the snow.
Photo courtesy of Stan Malcolm
This strategy does not appear to hinder the species, as Noctua pronuba is one of the most abundant moths in many parts of its range. The caterpillars appear to be stimulated into action by one or two “warm” days, which may be just above freezing. Perhaps they have become overly sensitive to temperature changes, causing them to emerge in the snow instead of waiting until spring?
While it might not seem like there would be food available to a caterpillar in January in the Northeast, these caterpillars are not picky. Many of them attack roots of plants. As an agricultural pest, Noctua pronuba may feed on exposed annual plants if they are not covered by snow. This might provide enough of an advantage to the caterpillars that it balances out potential mortality due to the cold and predation (a brown caterpillar is pretty obvious on white snow). But studies would have to be done in order to say for certain.
Have you seen any caterpillars on the snow? Have you seen any that are notNoctua pronuba?
And does anyone know if they also appear on the snow in Europe, or is it a behavior expressed only in North America?
Further reading: _______________________________________________
-Wagner, D. 2011. Owlet Caterpillars of Eastern North America, Princeton University Press, pg. 538.
-Diagnostic Services at Michigan State University
Life is getting more exciting here in the Wagner lab – moths are emerging! Every year we raise hundreds and hundreds of caterpillars for various projects. I am only directly involved in rearing my own specimens, but we have an army of undergraduates who help Dave rear caterpillars for his books and research. We have a “rearing room” in the lab where they are kept as caterpillars during the summer, and as pupae during the winter. Lately we have been increasing the photoperiod, heat, and humidity in order to encourage the moths to emerge a bit early. We are going to kill them to become specimens, and it’s nice to get all the pinning done before the field collecting season starts.
Today some lab members alerted me to this moth, a cute fuzzy species in the genus Cucullia (family Noctuidae). It had created its pupal chamber directly against the bottom of the plastic container amidst some paper towel. We thought this would make it easier for it to emerge, but it couldn’t seem to figure out what to do.
Its head appeared to be stuck, and it could not manage to break apart any other section of the pupal shell. We were about to cut it open to help, when…
Hurray! It emerged! It had to do some interesting yoga moves to flip around, but it got out of there in the end. It then took a few minutes to inflate its wings with hemolymph, and after a short time started looking like a regular moth.
Usually moths emerge at night in order to fluff up their wings out of sight of birds… so we had never seen a dramatic emergence such as this. Maybe it just needed some encouragement.
My schedule this semester actually allows me to spend long chunks of time looking at caterpillars. Finally! It’s really difficult for me to work on my morphological datasets in small bits of time (like one hour between classes/seminars). But three to five hours at a time with no interruption… glorious.
Aaaand we’re off – to see if some of my caterpillars are chemically protected.
This is my arm right now:
I’m about to go rub some caterpillars on another lab member.
(It’s ok, we’ve filled out the human testing protocol paperwork.)
So far I’m intrigued that these three species have all given me the same type of reaction in terms of timing, appearance, and sensation (it burns, and then itches). Other people in the lab have reacted to them as well, but I want to document this in a systematic fashion. It could be an important phylogenetic character. So far we’re pretty sure two of them are in the same clade, and the other we are going to add to our molecular dataset soon.
Here I am with some caterpillars (Acronicta impleta)… that I am about to start testing for chemical defenses by rubbing them on my arm. From a few reactions I’ve had, it seems there is one clade within the genus Acronicta which are chemically protected. I am still sporting a rash from a caterpillar I rubbed on my arm a week ago. For science!
Harrisimemna trisignata is an unusual animal. It has so many bizarre adaptations it’s difficult to know where to start. So, I’ll start with some pictures and a video, then give my thoughts. It is in the subfamily Acronictinae (family Noctuidae), which is why I am rearing it.
Harrisimemna trisignata appears to be a bird dropping mimic. Its coloration is beautiful to us, yet probably looks disgusting to a bird. It even looks like it has runny uric acid dropping down the sides of its body. However… it does not sit like a bird dropping mimic. Instead it arches its back, almost reaching its last segment with its head. Every time I look at my caterpillars, they are in that pose. They also have a bizarrely shaped pair of third thoracic legs. Not sure why?
Also, they have a habit of attaching their shed head capsules to the hairs just behind their head. As you can see in the video, they appear to use this head capsule as a mace to ward off attackers. Sometimes these capsules will stack on top of each other in a chain, though they usually fall off and they just have one at a time.
And they shake! They shake when I open the container, when I breathe on them, when I talk to them, when I touch them, when I look at them the wrong way. I can just imagine a potential parasitoid, like a tiny wasp, trying to land on that caterpillar… between the shaking and the head capsule whipping, I doubt it would stick around.
And of course the jumping spider mimic butt. Doesn’t it look like it has a few pairs of eyes on the back? In the last instar (the above photos are second to last) the appearance of a crouched jumping spider is even more dramatic.
They are also ball rollers. When they did their pupal chambers in wood, instead of just chewing up the wood like most caterpillars, they roll it up into neat little balls, then throw them aside. A few genera in the subfamily Acronictinae have this behavior. So far our molecular work has placed them at the base of the tree.
What does this all mean? This caterpillar is a remarkable animal which still has many more surprises in store, I am sure. I am really hoping to rear it again next year to study its behaviors.
For further reading:
I am so excited!!!
I just purchased a custom order from CaterpillarArts on Etsy. She opened up her shop a week ago, featuring beautiful little caterpillar pendants. When I saw her work I had to ask for my favorite species, Acronicta funeralis. I know it’s a tricky one, but AJ blew me away with how accurately she was able to re-create this caterpillar.
I can’t wait to get this little guy in the mail next week!
For comparison, here is a photo I took of a real Acronicta funeralis last summer:
Please check out her shop, more goodies are being added frequently – I just saw she has a few crystalids as well!