Dragonfly Swarms Revisited

Pantala flavescens

A wandering glider (Pantala flavescens) from the swarm I witnessed last summer.

Since I put out my request for reports of dragonfly swarm sightings a month ago, data have been streaming in!  I thought it was time to give a brief report of the dragonfly swarming activity in North America this summer so that everyone who’s sent a report in can see how much I appreciate your sending me reports.  I couldn’t be happier with the information that’s been coming my way, so thank you all so much for helping me track this behavior.  Keep the reports coming!

First things first.  In my next post, I’m going to cover a paper I came across on dragonfly migratory swarms in North  America from 1998.  I think it will give everyone a better idea of why these swarms might be forming and what they’re doing.  For now, just know that there are two types of swarming behavior:

  1. Migratory swarms. These are effectively rivers of hundreds of thousands of dragonflies all flying in a single direction and covering large distances.  These types of swarms are like bird migrations or the migrations of monarch butterflies – lots of individuals traveling together between habitats and usually made up of a single species or with one dominant species and a few other minor players.  These swarms move very quickly and may appear and disappear in a matter of minutes.  The dragonflies in these swarms typically follow significant waterways and fly high above the ground (20-100 feet).
  2. Static swarms. This is the type of swarm I reported on last summer and the type that prompted my interest in this behavior.  These swarms contain far fewer individuals than migratory swarms (20-1000 instead of tens of hundreds of thousands) and are highly localized.  Individuals in the swarm will remain restricted to a very small area (like one field or yard or hill) and fly in a circular or figure-8 pattern about 1-20 feet off the ground, usually over a grassy area.  These swarms are likely feeding swarms and may contain one to several species of dragonflies in about equal proportions.  (Please read the post from last summer linked above for a more detailed description of the behavior of the swarm I witnessed and a video.)

These two types of swarms, though very different, might be related to one another.  There are some striking similarities between the two types that suggest that this might be the case.  For one, the known migratory dragonfly species are the same species that appear to be making up the static swarms.  Also, both types of swarms occur during the same part of the year.  Last, both types of swarms seem to be weather related.  Almost everyone who has reported a swarm has also reported a recent storm or an incoming one, especially after a long period of hot, dry weather.  Weather is thought to play an important role in the migratory swarms as well.

When I wrote my initial posts on dragonfly swarms, I got a few reports from people who had seen them in other locations.  I also got several people stumbling onto my blog after searching for dragonfly swarms on the internet.  Last summer I got maybe 30 hits a week on my swarm pages and none at all for most of the rest of the year.  This year, I’m getting 500 hits a week!  Clearly, something is happening this summer that is making these swarms much more abundant and visible than they have been in the past.  I can’t, of course, say for sure why this is, but I suspect it has something to do with the weather pattens we’ve seen this year.  I saw a report on the National Geographic website a few days ago that said that this is the hottest year on record in the US – and we started recording weather data in the late 1800’s.  Perhaps the hot weather and the recent rains have something to do with the huge number of swarms (and the large size of some of these swarms) that have cropped up this year.

So what patterns have I been able to identify from the data I’ve collected from reports from readers?  There are definitely a few locations that have a lot of static swarming activity recently:

  • Eastern Missouri in the St. Louis area.  There seem to be many swarms within a massive area from slightly north of St. Louis south to the MO border and extending west to the central part of the state.  These swarms are highly localized when they appear and are often in one person’s yard or field and not in the yard/field next door.  The swarms have been made up of several different species and consist of several hundred dragonflies.  It has been quite hot in the area, but they’ve had some recent storms.
  • Northern Illinois/Wisconsin.  These swarms may be part of the Missouri action because they are very similar.  They also cover a large area, consist of mixed-species in highly localized areas, and they’ve been showing up after storms.  It’s been hot in this area recently too.
  • New Jersey.  These sightings seem to be completely unrelated to the swarms in the Midwest, but they’re spread across the state.  The swarms are a bit smaller than the Midwestern ones (20-100 individuals), but they’re often made up of multiple species and have appeared before or after storms.
Pantala hymenaea banking

A spot wing glider (Pantala hymenaea) from the Tucson swarm last summer.

Other sporadic swarms have been reported in Iowa, Ohio, Texas, Tennessee, New York, Connecticut, California, Pennsylvania, and Saskatchewan.

Based on the data I’ve collected so far, it looks likely that in many areas, there are very large, widespread groups of dragonflies.  The swarms people are seeing in their yards may be a subset of these larger super-swarms.  I’m starting to think this because I’ll get 20 different reports from one rather large geographic area all describing the exact same thing over the course of 3 or 4 days.  I’ll get another 20 reports from another area, all with similar descriptions and within a few days of each other.

I did also get several individual reports of a massive migratory swarm in downtown Little Rock, Arkansas earlier this week.  The accounts I heard suggest that the swarm was made up of truly staggering numbers of dragonflies, maybe hundreds of thousands or millions of individuals, that all flew right by the 6th floor windows of several buildings.  One reporter said he couldn’t see the building across the street as the dragonflies flew by!  They were all flying parallel to the river and in a single direction and the whole event was over in less than a minute.  Wow.  I would have given anything to see that!  If anyone else is lucky enough to witness an event like this, I hope you will send a report to me!  However, though I got many reports of this single event, they’re the only reports of anything like migratory swarms I’ve gotten all summer.  It appears that the static swarms are much more common than the big migratory swarms, but I think there’s a good chance that they’re related to one another.

And this is where you all come in!  Keep sending me your reports!  With your help, I might be able to get a better handle on the movements of my proposed super-swarms and determine whether the migratory and static swarms are actually related.  I might also be able to determine whether the Midwestern swarms are all part of one giant swarm or the Missouri and Illinois/Wisconsin swarms are separate.  Plus, I have a feeling this is a special year for this behavior and we might never see another summer like this again.  I’d like to collect as much data as I can now so that I can compare this year to future years and to take advantage of the abundance of swarms that are cropping up throughout the country.

Check back soon for the summary of the migratory swarm behavior paper!  Judging from the number of people who have been searching for information on dragonfly swarms on the internet this summer, it might be quite interesting for people hoping to explain the phenomena they’ve been seeing in their backyards.

(Want more information about dragonfly swarms?  Visit my Dragonfly Swarm Information page for my entire collection of posts on dragonfly swarms!)

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Have you seen a dragonfly swarm?

I am tracking swarms so I can learn more about this interesting behavior.  If you see one, I’d love to hear from you!  Please visit my Report a Dragonfly Swarm page to fill out the official report form.  It only takes a few minutes!

Thanks!

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Want more information?

Visit my dragonfly swarm information page for my entire collection of posts about dragonfly swarms!

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Unless otherwise stated, all text, images, and video are copyright © TheDragonflyWoman.com

Unless otherwise stated, all text, images, and video are copyright © 2010 DragonflyWoman.
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