2012 Dragonfly Swarm Project Year-End Report: Conclusions

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It’s time for part 3 of the yearly Dragonfly Swarm Project report! Today, I present the results of the predictions I made last year based on the data you all have contributed over the last 3 years, plus I’m proposing a challenge to you. Last year I made three predictions, so I’ll address those first, but then I want to get some feedback from YOU and see what you think. Ready? Let’s go!

This year was an interesting year in many ways, so the conclusions I thought were going to be so clear-cut and consistent from year to year aren’t necessarily as predictable as expected. That makes for exciting science though! The first prediction was the most straightforward:

Old Prediction: Dragonfly swarming will be most commonly reported east of the Missouri River in the U.S.

This is the one constant in this project each year. The space between the Missouri River and the Mississippi River typically produces several swarms each year, but I think it’s safe to make a new prediction based on the data gathered so far:

New Prediction: US dragonfly swarms are most common east of the Mississippi River.

As I stated last year, I think a lot of this has to do with the amount of water in the eastern US relative to the west. There is more habitat available to dragonflies in the east and likely more dragonfly individuals present in the wetter areas than in the arid west (though I don’t have data to back this up – will be looking through the literature for evidence). To have swarms, you need a lot of dragonflies in one area. You see dragonfly swarms in the west, but there are often identifiable special conditions that concentrate the dragonflies within an area at the time of the swarm. I have a few ideas about that that I’ll get to…

Old Prediction: Most swarms reported will follow flooding or heavy rains.

This prediction was… partially correct. While there were still reports of flooding or heavy rains in 263 of the 705 swarm reports made in 2012, you’ll notice that that’s not even half the reports. In fact, 314 reports indicated that there was no flooding or heavy rains in the area prior to swarming events, which suggests that rains might not play as strong a role in swarm formation as I previously thought. That said, I still think that flooding is an important factor and if you compare the areas of the country where flooding took place in 2012 and the location of swarms, there appears to be a nice correlation between the two. Sadly, I don’t possess the technical expertise to actually show that to you at this time, so you’ll just have to take my word for it. Based on the 2012 data, I have developed a new idea about possible factors in swarm formation, which I’ll discuss later. And I make this prediction:

New Prediction: 40% or more swarms will be observed after flooding or heavy rains in 2013.

I still think heavy rains and floods are a major factor in swarm formation, so I suspect that I will continue to get a lot of swarms reported that occurred with major rains/floods.

Old Prediction: There will be more dragonfly swarms reported from the northern Midwest (Minnesota, Michigan, Wisconsin, Illinois, Iowa, etc) in 2012 than in 2011. Similarly, there will be very few reports of swarms from eastern Ohio, Pennsylvania, Virginia, and West Virginia.

This prediction was based on an idea I had after two years worth of data collection: that areas where there were big weather events and massive dragonfly swarming in one year would not have many reports the following year when that massive swarming was due to flooding.  My idea was that flooding in an area might deplete the nymphal population that would emerge the following year. I made the prediction based on a comparison from two seasons and wasn’t sure it was going to hold true in 2012. However, I crunched a few numbers and made a few maps, and here’s what I discovered. In 2010, there was heavy activity in the north central US, with reports from Iowa, Minnesota, Michigan, Illinois, and Wisconsin making up 36.8% of the total reports for the year. Iowa and Illinois alone made up over 20% of the reports. In 2011, however, those five states made up only 7.8% of the reports. Things picked up in 2012 such that 18.9% of observations were made in the north central US. So, that part of the prediction was correct: swarming activity dipped strongly the year after the flooding in these states and then increased the following year. So far so good! But what about that second prediction? I have numbers if you are interested in them, but the map will show it so much more clearly. In 2011, a massive number of reports were made in Ohio, Pennsylvania, Virginia, and West Virginia, close to half of the reports. The map of the 2011 data in that area looked like this (click images to make them larger), and focus on the four states of interest, that big blotch of nearly solid green on the upper mid-Atlantic states:

2011 Static NE

Clearly, there was a major event happening in OH-PA-WV-VA, and indeed there was a lot of rain and flooding in that area that resulted from Hurricane Irene and Tropical Storm Lee. Lots of flooding meant lots of swarms in 2011. This is that same area in 2012:

2012 Static NE

Now THAT is a huge difference! Clearly there were far more swarms taking place in this region in 2011 than in 2012, so the second part of the prediction held true as well. The sample size is small and it’s hard to make broad conclusions without at least a few more year’s worth of data, but I think the data so far suggest that heavy swarming in a location one year results in low swarming the following year.

That said, there was no obvious and large center of activity this year. In fact, there were only two areas where large swarming events occurred: the New Jersey/southeastern New York area and Colorado. Comparing the 2012 data to 2013 data for Colorado isn’t fair because Colorado is a western state that doesn’t normally have a lot of swarming activity. So, I am going to make this prediction for 2013:

New Prediction: There will be fewer swarms in the New Jersey area in 2013 than in 2012.

Ultimately, however, the event in New Jersey wasn’t one the mega events you all have documented in the last few years, so it might not show the same sort of pronounced dip in activity highlighted in the maps above. Plus, the data from New Jersey is confounded because the eastern migration passes through the state in the fall.  We’ll just have to wait and see what happens!

I have a few ideas about why dragonfly swarms form and why they are important, but in the interest of keeping this post a reasonable length I am going to save them for another post. However, I promised you a challenge, and here it is: what do YOU think? I want to see if you all can come up with exciting, new ideas that I haven’t considered by answering two questions:

1. Why do static dragonfly swarms form? Feel free to list multiple suggestions for why they form at all, in addition to why they form in the locations where they have been observed. And…

2. What roles do you think static dragonfly swarms play in the environment? I.e., why are dragonfly swarms important?

I have my own ideas for about this behavior, but sometimes it’s good to get some fresh perspective.  That’s where you all come in! Feel free to base your answers on your own observations, the information I have shared on my blog, or any other source.  And just to keep things interesting, I’m offering a small dragonfly themed prize pack for a few of my favorite responses. If you want a chance at winning, offer some answers to the questions before 10AM EST Sunday, February 10, when I’ll post the reasons I propose for why these swarms form and why they’re important. I look forward to hearing your ideas!

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Unless otherwise stated, all text, images, and video are copyright © C. L. Goforth
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3 responses to “2012 Dragonfly Swarm Project Year-End Report: Conclusions

  1. Swarms in n WI & w UP of MI are usually tied to prey abundance, me thinks. No news I am sure, but will pay more attention to where, when, and who along w physical details. Coupled emergence peaks of predator & prey often along corridors such as roads near water bodies, based on casual obsv.

  2. Ma’am, to my untutored mind, you have to look at a couple of things. The first is the method of aggregation. What is the mechanism that brings large numbers of dragonflies together. Given that they live in habitats with limited visual horizons, I would assume that they are joining each other at or from altitude, which points toward some kind of dispersal. Hypothesis: Swarming is associated with dispersal associated with extremely high recruitment in a specific area. Are there any climatic predictors for “bumper crops” of dragonflies that could be linked to static swarm patterns?

    The second thing you have to look at is what they are doing. In my limited experience, static swarms are feeding heavily–like sharks on mullet–on midges. I have never made the effort to ID the midges, but I suspect that they are either Chironimid or Dixid adults that move away from the water and out over low areas in mating swarms. Hypothesis: Static swarms in large open spaces near water sources are feeding on aggregations of short-lived midges that have emerged and moved away from the water and out over low areas in mating swarms. Sadly, the piscatorial experts agree that midges are unpredictable in their emergence, e;g. “Midge hatches have no rhyme nor reason, they can hatch anytime of the day from early in the morning to late in the evening” [http://www.troutu.com/class/fly_fishing_midges].

  3. I wonder if swarming is a means of species maintenance. Do dragonflies swarm to keep the “bloislibes” pure? Now, my smartphone invented the word I attempted to enter just now between the quotation marks. In the dragonfly universe, some species anomalies occur. All the resources of my phone species came together to attempt a word. Do environmental factors mitigate against dragonfly DNA?
    I propose capturing and analyzing DNA of swarming versus pre swarming and post swarming ‘flies.
    Perhaps swarming is a form of natural selection.

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