Phenology: Yes, but Which Datana?

On the way into town this morning I saw an unusual caterpillar on the road. It looked as if it were trying to cross the four-lane highway from where it joins an exit ramp, not a very safe way for a caterpillar to cross a busy road.

It was about two inches long. Its ginger fur and yellow lateral stripe made it look like a fat, out-of-season Eastern Tent Caterpillar from a distance. Of course it could hardly be that. On a closer look, its skin was striped in orange-brown and yellow, with thin lateral stripes on all sides rather than the fancy pattern of a Tent Caterpillar. Its head and tail ends were orange-brown. It looked like one of the several laterally striped caterpillars in the genus Datana. While the Walnut Caterpillar, Datana integerrima, is black with white fur, sometimes very fluffy, several other Datanas are stripey with much shorter and sparser hairs.

Though I found closer matches elsewhere, here, for those in search of an immediate caterpillar gross-out, is a free photo of D. ministra from Wikipedia.

Shared at https://en.wikipedia.org/wiki/Datana_ministra by Gerald J. Lenhard, who says: "This image is Image Number 0014042 at Forestry Images, a source for forest health, natural resources and silviculture images operated by The Bugwood Network at the University of Georgia and the USDA Forest Service."

The test of a Datana caterpillar is how it squirms if threatened. The whole moth family to which this genus belongs, the Notodontidae, is recognized by the insects' tendency to arch their backs into a J or even a lopsided U shape. The caterpillars will raise their head and tail sections at the same time and squirm as if they thought they could bite and sting, although they're bluffing; like most caterpillars they're harmless if not swallowed. (They are, however, working themselves up to excrete little drops of bodywaste from each end. This blogger, observing one of the Datanas that is not stripey in its final stage, was able to photograph Datana major threatening him with a tiny blob of frass:

https://bluejaybarrens.blogspot.com/2014/09/army-of-caterpillars-datana-major.html )

But I didn't take the time to threaten the caterpillar I saw to see how it would react. It just had a Datana look. I walked on into town where I could look it up.

At least two Datanas are called "Yellow-necked" because the caterpillars have a yellow or yellow-orange patch or band just behind the head. D. ministra is fairly common in our region but its caterpillars are usually described as having black and yellow stripes and relatively short, sparse white hairs. Though soft rather than spiky hair is visible all over these caterpillars, it's hardly thick enough to be described as fur, as D. integerrima's and the Tent Caterpillars' hair can be.

The caterpillar I saw was more yellow than brown all over, but might have been described as yellow-necked. I looked it up on the Internet. Much remains to be learned. The first thing I learned was that D. ministra caterpillars are variable, with some color patterns--usually photographed at an earlier stage of life--that can resemble the ginger-and-saffron specimen I saw. Trigger warning: in the early stage little Datanas are very gregarious. They strip branches of host plants because they spread themselves over the plants, within touching distance of their siblings. When approached by a human, like the photographer whose report of this species is linked below, they go into their threat display for a major gross-out effect.

https://www.butterfliesandmoths.org/sighting_details/1226278

And of course the reason why lots of information about D. ministra is available online is that the caterpillars can be a nuisance. They usually eat azalea leaves but will also attack blueberry bushes. Like Walnut Caterpillars, when they strip branches or bushes in August or September they don't really harm the plant. Further south, where it's possible for caterpillars to hatch in spring, they can be a minor pest. Since they're harmless and usually found in easy reach, the recommended way to control them is to pick or shake them off the branch and kill them.

But...notice how irregular the brown dorsal stripe on those caterpillars in the photo looked? That's not mine. Mine had a smooth, even, yellow dorsal stripe...

I found web pages for the other Datanas but, as the moths and caterpillars all look very much alike and none of them is of great interest to farmers, I did not find clear photos or descriptions of the caterpillars. Mine could have been something less common than ministra, but nobody had taken the trouble to explain what. Photographs of D. drexelii (Drexel's Datana) caterpillars seem a closer match to what I saw, though not perfect.

https://www.butterfliesandmoths.org/sighting_details/1138384

There is no major economic difference between ministra and drexelii. One of those cases where both moths and caterpillars have almost identical looks, ranges, and habits; entomologists say they are two distinct species, but find it hard to explain why. (In such cases, sometimes there is a consistent difference in the body shape that's visible only under a microscope. Describing these differences would require entomologists to use technical language and grossly magnified images.)

There's also D. angusii (Angus' Datana), also very similar to ministra and drexelii, and some other species in this genus look remarkably similar to all three. Clear photos of the caterpillars of several species are not available. Photo galleries available for angusii, drexelii, ministra, and another confusible species contracta, suggest that the looks of individual caterpillars vary considerably. Further, because all the Datanas are most likely to be noticed in the early stages when they travel in packs, photos may be misleading with regard to final-stage caterpillars who roam alone. Consider the difference between next-to-last and last-stage D. major at the BlueJayBarrens Blogspot link above, or the fact that very young D. integerrima are red.

I'm guessing that what I saw was a full-sized drexelii who had been stuffing itself on somebody's blueberry bush, along with twenty or forty of its siblings. Squick per-yuckety urgh ugh ick, but no long-term damage, and little risk that this native species will proliferate and be more of a nuisance next year. All three yellow-necked Datanas and several of the other species are fairly common throughout Eastern and Central North America, but none of them seems to overpopulate in Virginia. As with integerrima, if we see them one year, that does not mean we're likely to see them again next year. Apparently our birds aren't intimidated by their group-squirming display.

I checked...although some people have described some of the Datanas as orange and black, they're another species that might stray onto a hibiscus bush during that final stage when caterpillars look for places far from their homes to pupate, but none of the Datanas is reported to eat hibiscus.

On the whole, the Datana I saw this morning seems to have been a harmless individual animal, doing its bit to maintain its species' insignificant place in our ecology by removing itself from the gene pool at an early age.

It would have been interesting, though, to have found clear descriptions of all the Datanas at all stages of their economically insignificant lives.