Pill Bug Mystery

Last November, we conducted a prescribed burn at a 3-year old restored prairie.  Two weeks later, I was surprised to be able to photograph green regrowth in that area.  Last week, I revisited the same burned area and got yet another surprise.  Thousands and thousands of dead pill bugs (aka sow bugs, roly polies, wood lice) lay scattered across the ground.

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Dead pill bugs in a prairie burned last November.

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The distribution of dead critters wasn’t consistent across the site, but there were a lot of areas like this with big numbers.

After I found the first few, I noticed them everywhere.  White skeletons of pill bugs, lying on top of the ground – sometimes in large aggregations, other times just a few here and there.  If I’d randomly tossed a hoola hoop on the ground 100 times, I bet I’d have found at least a couple dead pill bugs inside the hoop after 97 out of 100 of those throws.

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I think these pill bugs were probably Armadillidium vulgare, which is a pretty good descriptive name for them.

When I got home, I looked through my photos from last November to see if maybe the dead pill bugs had been on the ground back then too.  If they were still dark gray, instead of white, I might not have noticed them.  Out of about 30 photos, I did find one bug, and it was still dark.  It’s certainly possible there were many more bugs on the ground, hidden by a combination of their dark color and the remaining ash and debris that has since largely disappeared. I’d like to think I would have noticed that many, but I’m not very confident of that.

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A single pill bug can be seen in this photo from mid-November last year.

I like mysteries, but I also like understanding ecological phenomena.  Pill bugs are detritivores; they feed on dead and decaying material on and below the soil surface.  One possibility is that the dead pill bugs had been feeding above ground, within the layer of thatchy dead vegetation, and were killed by the fire.  A second possibility is that they were belowground during the fire, but came up after the fire (maybe it got too cold and/or dry because the protective thatch was burned away?) and then died aboveground.  There are lots of other possibilities as well, not all of them related to fire.

I emailed photos and questions to several entomology friends, asking for help explaining what I’d seen.  None had ever seen something like this after a fire.  Based on their responses, though, my first proposed scenario (above) seems the most likely.  I just wish I’d looked more carefully after the fire last November, though there wasn’t any reason to do that at the time!  One of my friends also mentioned that I shouldn’t lose any sleep over what happened since the pill bugs are an introduced species (native to the Mediterranean region) and could be having negative impacts on the native detritivore community in prairies.

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There were clusters of dead pill bugs in basal clumps of grasses like this one.  Maybe they got lodged here during a strong wind?

This is the kind of thing that keeps me interested in ecology.  Something killed a lot of pill bugs in that prairie.  It was probably related to the fire, but I can’t even say that for sure.  If it was the fire, were there other creatures similarly impacted, but in a less visible way? (We try not to burn entire prairies because of this kind of potential impact, especially on insects overwintering aboveground.) What impacts might the loss of that many pill bugs have on other detritivores, on the decomposition process in that prairie, or on other aspects of prairie ecology?  Lots to ponder; I love it!

Has anyone out there seen anything like this before?  Any other suggestions as to what might have happened?

PLANT GAME ANSWERS:

Thanks to everyone who played the plant game this week.  Over 360 people guessed on the first question, and over 60% guessed correctly that “Widespread Panic Grass” was made up.  Nice work, though I did purposefully try to make the first one easy.

The second question got many fewer guesses, only about 200, as of my writing this.  I got most of you on this one.  Almost half of the guesses were for Yerba Mansa, but that’s a real plant, folks.  It’s a rhizomatous semi-succulent plant in the lizard’s-tail family (Saururaceae) – I PROMISE I’M NOT MAKING THIS UP – and is most common in the southwestern United States, but has at least one record in western Nebraska.

The correct answer for the second question was “Jagged-edge milkwort,” which doesn’t exist.  It’s a little tricky because milkwort is a real thing, but there is no such thing as a “jagged-edge milkwort”.  Only 14% of guessers got it right.  Congratulations to you 30 people!

It looks like people enjoyed playing the game, so we’ll try it again in the near future.

Hubbard Fellowship Blog- Marvels in the Mud

This post was written by Evan Barrientos, one of our Hubbard Fellows.  Evan is a talented writer and photographer and I encourage you to check out his personal blog. If you would like to see more of his photographs, you can follow him on Facebook.

April 2nd was the kind of spring day where you triumphantly open every window in the house. I wanted to get out and explore somewhere new, so I drove to the Fort Kearny Hike and Bike Trail. When I arrived, a bored-looking family was slowly rolling down the weedy trail…in a golf cart. I despaired, thinking that I had driven half an hour to look at weeds with joggers huffing by. Nonetheless, I walked down the crowded trail for a couple of uneventful minutes minutes until it crossed over the Platte River. Much to my relief, there was a staircase inviting visitors to explore the sandbar below. I descended the stairs and started exploring the one place no one else was. It would be another three hours until I returned.

I began by walking in the thicker vegetation, hoping to flush some of the first insects of the year. As I did, several small spiders scurried away. I knelt down to look at them and noticed a few gnats mating on the blades of grass. After a long winter with no insects, these gnats were as exciting for me to photograph as Sandhill Cranes.

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Once I was on my belly, more details revealed themselves and a story began to unfold. A few feet from the gnats I spotted a muscid fly. I’m grateful that winter had made me so appreciative of even the common insects; otherwise I might not have taken a closer look. I did, however, and noticed that this wasn’t your typical potato salad-sucking housefly. It was devouring one of the gnats!

The calls of sandpipers drew my attention away from the microcarnage and I went over to the open part of the sandbar. There, I found a migratory flock of Baird’s Sandpipers foraging in the mud. I sat and watched them, wondering how they could possibly find enough food in the muck to sustain their 3,700-mile migration from Argentina. When they flew away, I thought I’d try to figure it out. A tiger beetle distracted me and I started stalking the speedy predator on my belly. Each time I would crawl close enough for a decent photo he would dart a few inches ahead. For several minutes this continued until he had led me to the muddy edge of the sandbar. There, with my nose inches away, it dawned on me how much amazing life that mud contained.

With my camera flat on the ground I spent an hour discovering and photographing insect after insect, many of which I had never seen before. I’m no expert, but I know my insect families fairly well. Yet two of these species were so alien I can’t even tell what order they’re in! If you know, please tell me!

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These muscid flies reminded me of sandpipers on a much smaller scale. Both patrol the same mudflats, probing the ground for food. The flies, however, let me watch them from inches away.

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This even smaller fly might be contributing to the sandpipers’ food supply. Occasionally I saw the fly press the tip of her abdomen to the mud, perhaps laying eggs or larvae that the sandpipers would certainly slurp up.

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Almost every one of these flies was paired with a mate. Presumably, the male is on top, guarding his female from other males while she tries to go about her life as normal. I don’t know that for sure, but I do know of another species that mates this way.

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This mystery insect delicately unfolded her cellophane wings in front of me. I have no idea what kind of insect it is. A beetle?

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Another mystery insect. I’ve never seen anything like this!

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At first I thought this little jewel was a tiger beetle, but I later learned that it’s a marsh ground beetle (Elaphrus sp.). Never seen one before!

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Springtails were the tiniest and most abundant invertebrates present, but finding them in my viewfinder was impossible because of their size. I only managed this photo because the springtail jumped into the frame while I was photographing the flies in the background.

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Above the muddy valley, a spider hunted for prey.

After completing my goal of photographing every species I could find in that puddle, I got up, stretched my very sore neck, and walked over to the other side of the sandbar. There, I found a small pool with about a dozen small fish huddled together (later identified by Chris as Plains Killifish, Fundulus zebrinus). I began crawling over to them but stopped when I heard some splashing coming from a trickle of water connecting the pool to a larger one. I went to investigate and realized that the splashing was coming from the fish as they struggled to swim through the shallow channel! Like tiny salmon, fish after fish darted through this passage. I wish I knew more about them, but I can only guess that they were on a reproductive migration.

The killifish were extremely wary and freakishly good at spotting me from underwater. I crawled up to their stream and lay still, waiting for them to swim by. I don’t know how they could see me so easily, but I learned that if I moved even the slightest bit they would panic and turn back. After many frustrating failures, I only managed to record a few mediocre videos of this fascinating behavior. To give you an idea of how quick these fish were (and how hard it was to photograph them), these videos are in slow motion at half-speed.

At this point my knees, neck, and elbows could tolerate no more strain. I walked back to my car smeared with mud and drawing lots of puzzled looks. But that was okay, because that mud had given me an afternoon of joy and wonder. If you ever find yourself bored in nature, I recommend you get off the trail and on your belly.