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September, 2015

The Mystery of the Purple Larvae

by Valerie

When it comes to observations of the natural world, a person might see myriad creatures or circumstances that they don't recognize, understand or manage to successfully place in the overall scheme of things. Much has been published on all manner of phenomena, and now that the internet has made research results more accessible than ever, the tools are often at hand but only if one knows where to look. I spend a lot of time exploring the environment around my central Texas home, and I frequently run across insects, plants, or behaviors that are puzzling. Sometimes I can figure it out; often I can start researching and will discover the answers to my questions; occasionally I contact experts and simply ask them. Rarely does a week go by that I do not find an insect or spider or other invertebrate that I've never seen before. Until I can place a name to a creature, it remains a mystery. And some mysteries last longer than others.

During my formative years, I took a keen interest in everything about nature. I especially liked vertebrates, but also enjoyed watching bugs and other small creatures, finding unusual plants and strange fungi, and even pondering odd fossils and rock formations. Sometimes I learned just what it was that I was seeing, and other times I would just make guesses. This system continues today. If I find something new, I look it up, using my best guess to get started in the correct direction.

After moving from Illinois to Florida and then, over 30 years ago, to Texas, I had more than enough new creatures to keep me wondering. Due to its central location on the continent, Texas has the highest diversity of arthropods in the U.S. There were colorful bugs, grasshopper nymphs, and beetles that were unlike anything I'd seen anywhere else. I first used my film camera and then later switched to digital photography as a tool to studying the fantastic animals I found.

Starting in 2000, I began making websites, and the most natural topics to put onto them had to do with the nature that I photographed in our yard. I not only put my discoveries online, but also my unanswered questions. As the internet was a much smaller community 15 years ago, I sometimes received advice or information via email from people that knew more than I did about what I had illustrated. I learned about owlflies, ant mimicking bugs, and purple sawfly larvae. This last creature was so strange that I did not even know what order to place it in. I simply found what looked like bright purple beetle grubs eating a plant called Velvetleaf Mallow in our garden. I put a photo in an essay about fuzzy plants and somebody wrote to me to tell me that they were probably sawfly larvae. At that time, I knew practically nothing about insects and surmised that they were related to the Elm Sawfly and so must be a Cimbex species. Wild, and totally wrong, guess.

Within a couple of years, I retired from teaching, took up digital photography, and started to study entomology in earnest. The networking made possible through the internet and email, along with frequent trips to the library, helped me learn an incredible amount about many of the animals in our area. Sites like BugGuide were wonderful because they allowed many people to work on identification questions. It was inevitable that the purple sawfly larvae would come to the attention of the BugGuide community.

Unfortunately, nobody seemed to be able to figure out just what those sawflies were. There are several families of these insects, which are related to wasps but do not sting. After studying the chapters on sawflies in a library book about immature insects, I tentatively placed the colorful sawflies in argidae. Then, in 2007, a friend named Dan raised some of the larvae to adulthood. Just like the lepidoptera he usually reared, these pupated after a short time and, when the adult emerged (looking exactly like an argid sawfly), he sent it to the Texas A&M insect collection. Time passed. I found more of the larvae, and discovered that they were green when they were small, only turning purple once they were full size before pupation. Other people reported them too and would ask what they were. All we could say was that they were argid sawflies that seemed to only be found in Texas. I even photographed what I thought was probably an adult on the host plant. It looked like a typical argid sawfly. No help there.

The larvae, although quite distinctive and easily noticed, do not appear all the time, or even every year. At least sightings of them are sporadic. This year, they appeared in several places around Austin, including at the LBJ Wildflower Center where I oversee a program called the Fauna Project. Interest in getting a specific identification was renewed. The volunteers in the Insectary raised some of the insects. Joe, one of the staff at the Wildflower Center, started asking around the professional entomology community. He also contacted a retired researcher who had written a very comprehensive summary on the argid sawflies of North America.

There is a funny aside regarding this researcher. I had, a couple of months before, attempted to find an expert who might be of assistance. I looked up scientific papers on argid sawflies and noted the author's name on the most authoritative, which was David Smith. In the past, I've been able to locate experts at universities or other research institutions this way and then contact them with questions. The number of David Smiths on the internet, though, made it difficult this time around. After some searching, I saw what I thought was an obituary for the person I was seeking, so I figured that was, quite literally, a dead end. It seems that I made a mistake and the David Smith who wrote the paper was not at all dead, but was instead the expert whom Joe contacted.

It turned out that David Smith had described and formally named the sawfly in question in 1971. At that time, he used pinned adults and larvae in alcohol (their purple color completely faded) from Texas. This same person, though retired, had been to Texas A&M a couple of years ago and had identified some pinned adult sawflies in their collection. An entomologist friend here in Austin named Mike knew of the specimen that Dan had sent there, and took the next opportunity to look for it. He found it, along with a label including a name: Neoptilia tora. Whew!

So now we know what the gorgeous purple larvae are called. We also know that there is a related species in the same genus that is found from Arizona into south Texas. That one has bright orange larvae that eat hollyhock, and the adults look pretty much the same except that they have orange abdomens instead of black. After all the time and the efforts of so many people, it is nice to have that little mystery solved. On to the next one.

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