Datana in the Birch

It’s caterpillar time. Although you can see caterpillars munching and crawling about the landscape from March to October, now is the time when you’ll encounter more of them in both numbers of individuals and diversity of species. Daily, people approach me with smartphone images, or even live caterpillars in their hands, asking “what is this?” Sometimes I know what it is, other times I don’t.

Fortunately, if I don’t immediately recognize what it is they hold in their hands or have captured on their phones, I can usually figure it out with a fair amount of quickness. The one reference I rely on most, the first one I go to, and the one that hasn’t let me down yet is Caterpillars of Eastern North America, David L. Wagner.

Don’t get me wrong, the internet is very useful. I often go back and forth from lepidopteran website to lepidopteran website, and insect site to insect site checking images. Caterpillars can vary in their color and do vary, specifically, in that respect according to age. So, looking at many images can help narrow down your choices when searching for a match (a word of caution–believe it or not, some images on the web may be labeled wrong).

It’s an old fashioned book that usually gets me started. You can easily flip back and forth from page to page in books, and I find reading from a written page much easier than scrolling up and down on a computer or phone screen. But both have their uses and it’s often a combination of the two, one confirming the other, that seals the deal on an identification.

Lepidoptera have five or fewer pair of prolegs.

So, what are the caterpillars in the photos on this page? The caterpillars were fifteen feet up in a birch tree, there’d be no close, in-hand viewing. Out comes the camera, get a photo and enlarge. The first thing I had to do was make sure they were caterpillars and not sawfly larvae.

Sawfly larvae have more than five pair of prolegs, that is, false legs used only in the larval stage of life. Lepidoptera have five or fewer prolegs as larvae (caterpillars). The larvae in the birch tree, in the photos, have five pair of prolegs. They’re caterpillars.

Next, the caterpillars appeared to be datanas, a type of moth in the Prominent family of moths. They’re gregarious feeders (they feed in groups or clusters). They all have stripes down the length of their bodies and are hairy to some degree. But, which datana?

Caterpillars of datana species are very similar. Their differences have to do with the color of the prolegs, color of the prothoracic plate behind the head and a few other characteristics (which needn’t be gotten into here, I’m confused enough). Despite my confusion and to complicate things further, the caterpillars may be different colors in various stages of their larval life. Pictures in books or the internet don’t always include all of the different stages of caterpillars lives and their concomitant color changes. What I was looking at had brown or orange and yellow stripes. One mark that seemed significant was the orange patch behind each caterpillar’s head (arrow in photo below).

Prothoracic plate.

Three days later I was back under the tree the caterpillars had been munching in. They were gone. Or, I thought they were gone. I searched the tree branches and couldn’t see a one. Later that day I noticed copious amounts of frass (caterpillar poop) under the birch tree the larvae had been feeding in. They were somewhere in that tree.

Where there’s frass, there’re caterpillars.

I finally located a handful of the insects. They were now black with yellow stripes. They had molted into their final caterpillar stage. Apparently, their gregariousness doesn’t carry over into their last stage of larval development, they weren’t all lumped together as before. Of course, due to their munching, there were now fewer leaves on the branches of the tree causing the caterpillars to spread out in search of fresh leaves.

After the molt.
This one had fallen from tree.

I was now ready to put a name on these caterpillars, yellow-necked datana (Datana ministra). The identification is based on the color of the prothoracic plate, proleg color, general coloration and foodplant (birch). Have I overlooked anything?

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