Monthly Archives: March 2013
I have determined that a friend of mine, who works in another lab, has access to materials I could use for inflating caterpillars. I can’t wait until the collecting season starts and I can start on my own specimens.
While some inflated caterpillars are curated within the main collection, and some of them are grouped by family in the larval cabinets, there are many “miscellaneous” drawers with arrangements like this.
All sorts of caterpillars! The nice green color of the swallowtail caterpillars (bottom right-ish) was not preserved though. This seems to be one limitation of caterpillar inflation – patterns remain, but colors become lost or distorted. Most inflated caterpillars are some shade of tan/brown. This could be due to the heating process or simply by fading over time due to light exposure.
One thing I did not expect to see – everted osmeterium! Swallowtail caterpillars (Papilio) have an eversible gland called the osmeterium which is normally held inside the body. When threatened, the caterpillar sticks out the two forks and tries to touch the attacker – wiping them with smelly defensive chemicals. Just the smell could be enough to deter a would-be predator, but I’m sure the taste is pretty bad too.
Many of the geometrid caterpillars were preserved in their usual hunched position. I wonder if this was induced somehow during the heating process, or if they simply inflated into the most natural position?
I couldn’t help but include a photo of the megalopygids (fuzzy guys on the right). Preserving them must have been a delicate task, hopefully carried out with gloves – they can give quite a vicious sting! They look more like little mice than insects, and each hair can leave a welt on your skin. I was tempted to test whether old preserved specimens would still sting, but decided not to try.
Have any of you ever inflated a caterpillar specimen before? If yes, do you have any advice?
One of the great things about being an entomology graduate student is that going behind the scenes at natural history museums is not only a perk – it is virtually required. Visiting a museum collection means new professional contacts, new collaborations and inspiration, examining specimens, and sometimes borrowing specimens to study at home.
Last week, during “spring break” (grad students might get breaks from classes, but never a real break from work) some members of our lab took a trip to the Smithsonian National Museum of Natural History. We drove from CT to DC, stayed overnight at a cheap hotel, and spent the next two days frolicking amongst the insect cabinets. Well, maybe I was the only one frolicking.
Plenty of room to frolic. Carefully.
I actually only spent about an hour, on the second day, exploring the public exhibitions. It was much more fun being behind the scenes, especially with the vast amount of specimens available to explore.
The Smithsonian NMNH holds over 35 million insect specimens in drawers, vials of alcohol, and slides – making it one of the largest insect collections in the world. You can read about the History of the United States Entomology Collections here.
I went to the museum with one major purpose – to see which caterpillars in the genus Acronicta they have preserved in alcohol, and if there are any species I have not yet examined and could borrow for further morphological study. Caterpillars are not often kept in collections (at least not in the same numbers as the more popular adult butterflies and moths) but luckily, the NMNH had what I was looking for.
There were 24 jars of ethanol holding Acronicta caterpillars, each jar containing up to a few dozen small vials with preserved specimens. I looked at every single vial, feeling the familiarity of old friends and the excitement of species I had not yet seen. Some specimens were collected by the authors of a seminal work on Acronicta published in 1898, Smith and Dyar. How cool is it to examine specimens collected by your heroes? I was amazed by the dates on some specimen labels – the oldest I found was collected in 1886.
This caterpillar is 127 years old.
With a spot to sit and look at specimens, the first day absolutely flew by. The entire evening of dinner and sight-seeing in DC felt like wasted time – I wished I could have stayed at the collection. Maybe if I had curled up to sleep under a desk, no one would have noticed?
Science is happening here.
The caterpillars were not just in jars, though. There were also a few drawers of inflated Acronicta larvae from around the world. I took lots of photos, but the memory card from my good camera is currently misbehaving. Hopefully I can recover the photos, though I could always retake the photos on another visit.
Some of the inflated Acronicta caterpillars.
I also met some wonderful people at the museum, and caught up with colleagues I have not seen for months or years. We had some great conversations about field collecting and project ideas. I learned a lot about collecting cave insects while walking through mountains of bat guano – did you know that rabies can be spread through the air? Sometimes entomology can be quite hazardous.
At one point I noticed a toy caterpillar on a shelf in the work room, and gushed over its accuracy and adorable-ness. Later in the day when I returned to my work station, I noticed it sitting on my laptop. My lab members told me I was given a new friend!
Cerura vinula, the puss-moth caterpillar, family Notodontidae. It now happily lives in my office.
The second day was as wonderful and short-lived as the first. I took many more photos of inflated caterpillars, which I will detail in another post. I felt so honored to be allowed to visit and explore such a historic institution, and hopefully will have many more visits over the course of my career.
Here is a treasury I made on Etsy, featuring girls who like bugs. Lots of cool art prints and greeting cards. I wish I had seen artwork like this when I was a kid, would have been encouraging to know I wasn’t quite alone.
Click here or click the photo to go to the treasury and see the individual listings.
Searching for “caterpillar art” on Etsy brings some interesting results. Check out MadebyMischief for more cool collages, often featuring bits of insects.
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.
I created this treasury on Etsy today, with works of art that feature collections of insects. Some are originals, prints, photographs, there’s even a t-shirt! Click the image below to go to the treasury and investigate individual listings.
You have four days left to listen to this fun program on BBC Radio 4. It is 30 minutes about naming insects, led by Dr. George McGavin, including interviews with several entomologists, even a member of the ICZN (International Commission on Zoological Nomenclature)! Some of them explain their justification for creating silly scientific names, like Pieza rhea Evenhuis, 2002 (say it out loud).
I particularly like the point at the end, about teaching children scientific names. We already do that with dinosaurs, why not with insects? If a child can learn how to say Pachycephalosaurus, surely they can learn Danaus plexippus (the monarch butterfly). The next time I do outreach with kids, I’m going to make an attempt at teaching scientific names and see how well it catches on.
Continuing the theme of “ok, some insects do come out during the winter”, a couple weeks ago our lab conducted our yearly boreid hunt. Once again, we achieved success!
Boreids are the winter scorpionflies, in the family Boreidae. They are primarily found as adults in late winter/early spring, when snow is still on the ground but the weather is warming up. They are uncommon in collections because not too many people go hunting for them.
We have experimented with various techniques for finding them. We have seen them jumping from moss at the base of trees onto the snow where they become visible. So we went outside and started looking at trees…
The boreids were elusive at first, despite the perfect conditions. We scraped bark and moss, dug through leaf litter, and scanned the snow around (almost) every tree in the area.
We kept getting distracted by other little creatures, the winter stoneflies, family Capniidae. They hurried to and fro across the snow, I wonder what they were looking for?
Finally – the prize!
A cute little female winter scorpionfly.
Piotr Naskrecki has also found some boreids in his neck of the woods, check out his blog to see much better photos than mine.
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
Winter is a slow time for caterpillar news in the Northeast. Most lepidopterans overwinter as eggs or pupae, and any overwintering caterpillars are usually hiding in the leaf litter. As a child I never liked winter very much, because there are very few insects to find. What’s the point in going outside if you can’t catch bugs?
However I still get some caterpillar identification questions from around the world. If you have a question of your own, send along a photo, I enjoy a challenge!
I nearly squealed when I saw this cute caterpillar in my inbox:
Photo courtesy of Katie Roller, Johannesburg, South Africa
This caterpillar hails from South Africa, a country I would love to visit someday (and some of my Acronicta caterpillars can be found there!). It appears to be Hippotion celerio, in the family Sphingidae, the hawk moths. Sphingid caterpillars are large and often have a “tail” at the end of their bodies. If you live in the US you are probably familiar with the tomato and tobacco hornworms, genus Manduca – they are fat green caterpillars, and big garden pests.
I found this video of Hippotion celerio in action. It’s pretty cool how the body can stretch out, and then retract to look more like a snake-mimic. If you want to learn more about caterpillar eyespots, check out Tom Hossie’s blog about his research!