I spent much of last week at the Niobrara Valley Preserve. One afternoon, I found myself with a couple hours of free time. It was cloudy, but bright enough that I thought I’d explore one of the many creeks that flow from underneath the Sandhills into the Niobrara River. Those creeks emerge from springs and flow downward through deciduous woodland in what are locally called ‘springbranch canyons’.

Because the streams come from groundwater and then flow through sandy channels, the water is very clear – an unusual situation in Nebraska. The combination of clear water and autumn leaves always makes these creeks fun to explore in October. Photography along their banks is tricky, though, because they’re shaded by both trees and topography.

To an open-country photographer like me, who is used to using early and late day light, that presents a real challenge. During prime post-sunrise and pre-sunset light periods, everything is in shadow. If I wait until the sun is high enough to hit the stream and its banks directly, the light is usually too intense, and the contrast between light and shadow overwhelms a camera’s sensor. The best opportunities I’ve found for photographing these creeks is on cloudy days.

That was a really long explanation for why I decided to hike up a couple creeks. There’s really no need to justify anything. It’s never a bad idea to hike along a creek!

It had been a frosty morning, so I was curious to see what kinds of small animals were moving around. I saw several cricket frogs (and managed to photograph a couple), but also a fair number of small invertebrates. There were lots of flies, of course, but also a mayfly and various other insects I wasn’t sure would still be active. I spent a few minutes trying to track a little red velvet mite on a rotting log that didn’t feel like sitting still for a photo. Eventually, I managed to capture a couple sharp photos of it.

My boots and lower legs got muddy very quickly. The steep topography along much of the creeks meant that I often walked through the water, or along the soft banks, where I frequently sank a foot down into muck. I didn’t mind a bit. Climbing around on steep and soft ground was a nice, but pleasant, workout. I also wore rain pants so I could easily kneel or lie prone on the ground to photograph things like frogs or mushrooms.

One of the springbranch canyons I hiked hosts a population of paper birch trees, a species that really shouldn’t be in Nebraska anymore. It’s a boreal species that still survives in the cool, moist environments of the Middle Niobrara River Valley. Well, I say it survives, but that survival seems awfully tenuous these days. The future of these populations is probably not bright in this particular location, given climbing global temperatures, but we’ll enjoy them while we can.

There are a lot of plants and other organisms along these creeks that I don’t see in prairies, so I didn’t know a lot of their names. I get so used to recognizing the identity of species around me (almost unconsciously) that it was a little jarring to be just a few hundred yards from familiar prairie species but unable to name much of what I saw right next to me. I’ve explored these creeks enough that I’d seen the species before, but haven’t had time or opportunity to really get to know them. Besides mystery plants, I came across a lot of mosses and fungi, along with (I think) slime molds, liverworts, and other exotic-seeming organisms.

I ended my hike at a small waterfall at the bottom of the second creek I explored. I liked the juxtaposition of golden leaves and rocks in the stream with the falls behind them. Since I was going to walk back to headquarters to change clothes, I took a few extra chances. I laid on the ground with my hips right on the edge of the creek and my torso hanging over the water. I stuck one elbow on a rock and tried to make all of that stable enough to facilitate taking a couple photos. I didn’t come away completely dry, but I was a lot less wet than I could have been.

I still prefer to wander and photograph prairies, but it’s fun to mix things up, too. An autumn walk through a springbranch canyon was a pretty great way to spend an afternoon. Especially because I was back in the prairie for sunset that evening. I don’t know how people manage to live where sunsets always happen behind trees or ridges. I guess those people probably wonder how people live where there’s nothing to block the wind… Each to their own, I guess.

Alliteration is fun, huh? So is the pursuit of mysteries, especially in nature.

Three years ago, I wrote a post about multitudes of fuzzy caterpillars at our family prairie. Many of them were crawling high up into the vegetation and dying, leaving behind desiccated dead bodies, still clinging to plants. It was morbid, but fascinating. I haven’t seen that phenomenon again – until this year.

In late September, I traveled out to our prairie to do some seed harvesting. As the sun was setting and I was walking back to my truck, I nearly fell over as I spotted a fuzzy caterpillar right in front of me and contorted my body so as not to squish it underfoot. Immediately, I noticed several others nearby.

Within an area the size of my pickup, there were easily 20 or 30 caterpillars that I recognized as larvae of the Virginian tiger moth (Spilosoma virginica). I could only identify them because I’d seen lots of them three years earlier, and that experience stuck prominently in my mind. It was too dark to photograph the caterpillars that night, but I came back the next morning with my camera and chased (ok, that’s an exaggeration) them around for a while.

I started my early morning caterpillar exploration where I’d seen the big group the night before, but as I wandered around, I found that the congregation of them was much bigger than I’d thought. They weren’t uniformly distributed, but they were spread across several acres of prairie. In some places, I found as many as 4 or 5 per square foot, while in others, I’d walk several steps between sightings. Still, that’s an awful lot of caterpillars – thousands of them, for sure.

My ecologist brain was curious about what they were feeding on. At first, I was mainly seeing them on yellow sweetclover plants (Melilotus officinalis), chewing busily away at both leaves and stems. That was handy because it often positioned them off the ground a little bit, and gave me good angles for photography. As I kept looking, though, it was clear their diet was much broader. I saw them feeding on lambsquarters, some kind of pigweed (Amaranthus sp.), green milkweed (Asclepias viridiflora), a species of dock (Rumex sp.), a knotweed (Polygonum sp.) and western snowberry (Symphoricarpus occidentalis). That’s some serious variety.

The feeding behavior was interesting, but that’s not what I was really looking for. I wanted to find evidence of the same ‘crawl-up-high-and-die’ behavior I’d seen three years earlier. Ok, to be clear, I wasn’t rooting for that, necessarily – that would be mean. I just didn’t want to miss the opportunity to see it if it was happening. I also hoped to get a little further in the investigation into what was causing the phenomenon.

Sure enough, as I walked around, about 5 or 10% of the caterpillars seemed to be dead – most of them at the top of plants, or even fenceposts. Some looked like they’d just recently died, but a few had clearly been there a while and had a kind of freeze-dried appearance. I took a few photos and then grabbed one of the dead ones to bring home with me.

As luck would have it, I was talking to former Hubbard Fellow Evan Barrientos shortly thereafter, and was reminded that he’d introduced me to Dr. Enakshi Ghosh earlier this year. Dr. Ghosh is a Post-doctoral researcher at the Natural Enemy Ecology Lab at Colorado State University. She studies cool things like parasitoid wasps that affect caterpillar populations. Evan helped me reach out to Dr. Ghosh and that email conversation led to me returning to the prairie to grab more caterpillar samples.

The next day, I shipped some caterpillar corpses to Colorado (that’s a normal, socially-appropriate thing to do, right?), hoping to solve the mystery of what killed them. A few days later, I got an email. Unfortunately, Dr. Ghosh wasn’t able to magically deduce exactly what had happened, but I did learn some things. First, she pointed out that the corpses were hollow – “which is a sign of developing parasitoids eating up their organs.”

In addition, she said there was a secondary fungal growth on them. I’d noticed that as well – it looked like some of them were covered with whitish powder. I wondered if that might somehow be tied to the parasitoid, but Dr. Ghosh didn’t think so. She also couldn’t find or examine the hole(s) used by parasitoid larva(e) to exit the carcasses after their death, probably because the caterpillar bodies had dried up too much.

The mystery isn’t fully solved yet, but I feel good knowing that it’s a parasitoid-related case. Unfortunately, I didn’t get back out to our prairie before it froze last week, so I wasn’t able to grab some living caterpillars and see what came out of them. I apologize for that dereliction of duty. Maybe, in another three years (hopefully less??) I’ll get another chance.

Should I use ‘less’ or ‘fewer’ in that last sentence? If I was talking about something like mosquito bites, I’d say “hopefully fewer”. Especially with mosquito bites. It should probably be ‘fewer’ when I’m talking about years, too, but my brain is telling me that we’re talking about an amount of time, and it’s appropriate to say “less time”. But since ‘years’ is the unit, I suppose it should be “fewer”. Let’s just all pretend I said “fewer” and I’ll move on with the story. Also, please ignore the irrational use of single and double parentheses in this paragraph.

In the meantime, I’m left to wonder why I don’t see this event every year. Are the caterpillars (and their parasitoid) in our prairie annually, but I don’t always see them? That’s sure possible, but I walk around that prairie a lot, and it seems a little wild that I’d miss big caterpillar congregations that span several acres.

Also, where did all the caterpillars come from? I mean, I know how they came to be, but was it a particularly big year for adult tiger moths this year? I photographed one in town, but don’t remember coming across hordes of them out at our prairie. That doesn’t mean much, of course. I could easily have missed them (they’re small and often sit low in vegetation during the day). Plus, I don’t know how many adults you need to lay enough eggs to explain the caterpillar abundance I saw this fall. Or, maybe it’s more important to wonder whether a disease organism or predator was less abundant this year, and not able to reduce the caterpillar population before it started.

As I say all the time, I don’t need to know all the answers. It’s the questions that make this fun! Even when I do get answers, those inevitably lead to more questions, so there’s no risk of running out. Let’s all just keep trying to observe, question, and investigate. These days, it’s easier than ever to find information about observations, especially with more apps to help us identify species and lots of online information. And, of course, in my case, I’m super lucky to have smart friends who agree to lend their expertise to my questions and save me lots of time.

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….By the way, if you think this story is amazing, just wait. I’ve got another story to share soon that will blow your mind! I’m hoping for a few more photos to wrap that story up, but I hope to post something about it within the next week or two, regardless of my success or failure.

I’m obviously very grateful for Dr. Enakshi Ghosh’s generous help with this. Not to provide too much of a spoiler, but she’s also connected to the other story I’m working on…