• Andy Davis

A couple of cases of curious caterpillars

Hello everyone,

Apologies for the lull in posts - the kids have been sick this past month. But this posting should get your monarch (and queen!) juices flowing! Have you ever seen an odd-looking monarch caterpillar, and thought, I wonder if this is normal? How about a crazy-looking queen caterpillar? Well, today I'm going to tell you about two cases that I've been personally involved in where this happened, and where I helped to get these observations published in scientific journals.

First, take a look at this beauty - a monarch caterpillar. See anything unusual about it?

If you haven't noticed it already, this monarch caterpillar has an extra set of tentacles on its 4th abdominal segment. Technically these tentacles are called tubercles in caterpillars. But whatever they're called, they shouldn't be there! Crazy, right? About 15 years ago, an undergraduate brought this to the lab from her parent's house in Florida. She had been working in the monarch lab for a while so she knew her way around monarch larvae, and what they looked like. Apparently, her parents had milkweed in the yard in Florida (tropical milkweed!) and when she looked for monarch larvae on them she came across this. I recall she eventually found some others (11 in all) and brought them in as well.

So neither Sonia nor I had seen anything like this before. So we raised them all in the lab just to see what happened. I recall they all ate pretty normally, and eventually they formed normal-looking chrysalises, then turned into normal-looking adult monarchs - no extra legs or anything. They were a little on the small side for monarchs but otherwise pretty normal. We didn't conduct any other tests on them, because I recall we were busy with other projects at the time. But I later helped to get the story published in a scientific journal - the Florida Entomologist. The link to the paper, which is downloadable - is here. Recall from previous posts of mine that I am a firm believer in publishing these kinds of observations, so that they are preserved for all time.

We never did figure out what was going on with these larvae. We suspected they were from a rare hybridization of monarch and either queens or soldiers, which also inhabit that region, and whose larvae have 3 tubercle pairs.

A few years later, someone found another monarch with extra tubercles and sent around a picture of it, which led to some more email discussion among monarch researchers, including Dick Vane Wright - the guy who literally wrote the book on milkweed butterflies. He had some thoughts on this, which I'll share:

"I think it most parsimonious to assume, rather like eye-spots in marginal wing cells of adult nymphalids, that all segments of the larva, from 2 to 11 (with the possible exception of 4), have the potential to produce a pair of tubercles. However, within most lineages (species, species groups, subgenera) a given arrangement (formula) is normally stable -- and, given the observed possibility for variation, thus under stabilising selection. This then raises the issue, again, what are they for, what do they do? I guess we must presume that they have some 'external' adaptive function (anti parasitoid or whatever), rather than represent some 'internal', developmental constraint.…" -Dick.

I don't recall this discussion moving much beyond that. Now I'm sure there are people out there who rear a gazillion monarchs in their kitchen each year and who have pictures of crazy-looking monarchs like this. Before you go sending them to me, let me tell you that this is something I don't have a lot of knowledge about and that I wouldn't know what to do with them! On the other hand, perhaps it would be nice to know how frequent this is, and if it is more frequent in reared monarchs vs wild ones, and if it only occurs in regions of the country where all three species (monarchs, soldiers, queens) overlap... hmmm...

OK, now how about a more recent case. A few years ago, Kip Kiphart from Texas, whom everyone in the monarch business knows, sent me pictures of some crazy-looking queen caterpillars he and some folks found near Boerne, TX. Here's one below.

Apparently, Kip and some of the volunteers at the Cibilo Nature Center had found some of these "red queens" (that's what they called them, and it has since stuck) while surveying their milkweed patches back in 2010. They knew these looked different and so took some photos. Then Kip found some in his backyard that same summer. Then someone else saw some in 2013, and then again in 2016. So they keep finding these in central Texas.

I worked with Kip to get these observations published in a scientific journal, and the paper was just officially published this year, in the journal, Tropical Lepidoptera Research. I'll put a link to the paper here

We had a couple of goals for the paper: first we wanted to describe the caterpillars as best we could, and we included all of the photos. Second, we wanted to figure out if anything like this had been seen before, or essentially how normal is this? For this second part, we examined online photos of queen caterpillars that people post to their Flickr accounts, or blogs, or whatever. We basically just googled the words queen caterpillar. You should try this - it's very illuminating. Then we went through each image and categorized it based on the color patterns. Below is a composite image we made for the paper. This image shows all of the "normal" color patterns for queens that we found. You'll note that there are no red queens, but there is a great deal of natural variation in color patterns.

By the way, I obtained formal permission to use the photos above, and I'll copy the statement from the paper that acknowledges the photographers.

"All photos were used here with permission. A. Round Rock, Texas (Joseph Kilgus). B. Scottsdale, Arizona (Gene Hanson). C. Pima, Arizona (David Bygott). D. Biscayne Park, Miami, Florida (Susan Ford Collins). E. Dallas, Texas (Dale Clark). F. Pima, Arizona (Michael J. Skinner). G. St. Catherines Island, Georgia (Christa Hayes). H. Thomas F. Riley Wilderness Park, Orange County, California (Jay Cossey)."

As you can see from the photos, there wasn't a clear "normal-looking" image to go on. So in the end we concluded that that queen caterpillars just seem to have a great deal of NATURAL variation in color, and the red queens of Texas (that sounds like a song title!) just represent an extreme form of this variation. In other words, they're not a mutant or anything. Maybe Kip and his team can do some more digging into this and figure out what's up with these red queens. Incidentally, I voted to call these the "Kiphart form" of the queen, but Kip voted me down.

Well, I guess that's it for today. I hope this blog will make you look more closely at the next monarch or queen caterpillar you see.

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Direct link to this blog entry:

http://akdavis6.wixsite.com/monarchscience/single-post/2017/03/11/A-couple-of-cases-of-curious-caterpillars

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The science of monarch butterflies

A blog about monarchs, written by a monarch scientist, for people who love monarchs