Happy new year everyone! This year New Year’s Day also happens to be Science Sunday, so I’m going to start 2012 off with a science filled post. Woo, science! :)
Every now and then, I’ll get an e mail from someone during the dragonfly swarming season telling me a story of how the writer walked outside and had a dozen or so dragonflies follow him/her closely as he/she walked. Most of the people who have this experience think it’s rather magical, but it’s unexpected and they want to know what’s going on. Happily, this behavior has actually been covered in the scientific literature! So, I’m going to start the new year by discussing a paper that deals with this interesting behavior that was released in the odonate science journal Odonatologica in 2010, authored by O and J Holusa of the Czech Republic.
For those if you who have followed my Dragonfly Swarm Project, you know that dragonflies often swarm because there are a lot of small prey insects in the area that attract them, forming a sort of all-you-can-eat buffet for lots of hungry dragonflies. In essence, the dragonflies are taking advantage of abundant food that is easy to capture. Swarms just happen to form if there is enough food for several dragonflies to eat.
A similar behavior called accompanying has been documented by a few odonate researchers. It works like this. When a large, slow-moving animal such as a hippo, rhino, or human walks through an area, two things happen. Insects that are attracted to the animal, such as blood sucking insects, follow them as they move. Other insects, those found on the grass, brush, or ground, also move out of the way by flying, jumping, or running. Small clouds of flying insects therefore form around the large animal as it moves. If you’re a dragonfly, these little clouds of insects are a great source of food. And, if you are a dragonfly that lives in an area where there are few bushes and flying insects are unlikely to move around much during the day, accompanying large, slow-moving animals means that you’re more likely to catch a tasty snack than if you wait for the little insects to fly on their own.
Brachythemis leucosticta. Photo licensed under Creative Commons by F. Lo Valvo and is available at http://en.wikipedia.org/wiki/File:Libellula.jpg.
One species of dragonfly, Brachythemis leucosticta, has been well documented performing this accompanying behavior, following large mammals within its African range. It tends to live in open, sparsely vegetated areas where movements of large animals could improve prey capture rates. The Holusas were curious whether the European populations of B. leucosticta would exhibit the same pattern of behavior. They also wished to document how far the dragonflies would accompany a large mammal and whether males or females were more likely to take part in the behavior.
They performed their very simple experiment with a population of B. leucosticta along the River Barbate in southern Spain. They started in the area where the dragonflies perched in the shade near the water and walked perpendicularly away from the shore. When dragonflies followed them, they counted the number of individuals, determined the sex of the followers, and recorded the distance at which each dragonfly returned to its perch. The researchers walked to the end of the floodplain and then made a wide arc back to the starting point, repeating the walk many more times over a two-day period.
With this experiment, the authors learned that dragonflies would usually follow them away from the water, flying close to the ground in front of them. Fewer than 5 dragonflies would usually follow the researchers, but they recorded one group of 11. Females were more likely to accompany than males, making up approximately 67% of the total observations. Females also accompanied further than males (up to 111m in famales and 89m in males), though both sexes typically returned to their perches before the researchers had traveled 40m from the water. Finally, of the 53 walks where dragonflies accompanied, dragonflies were observed catching and eating prey in only 3.
The authors made a few conclusions. First, they noted that though the prey capture rate of accompanying dragonflies was rather low, less than 2%, this was probably a higher prey capture rate than they would experience without accompanying. They also pointed out that few insects flew out of the grass as the researchers walked and the dragonflies captured prey every time small flying insects were observed. Accompanying is therefore likely a valuable means of capturing prey in a habitat that is rather inhospitable for small flying insects.
The authors also attempted to explain the differences in accompanying distances they observed between males and females. They suggest that because the females are lighter colored than males, they are not as noticable to the prey and are more successful at capturing prey via accompanying and therefore persist longer. They also suggest that because the males are darker, they heat up more quickly upon leaving the shade. I personally think this is highly unlikely, so I’d like to add a third possibility: that males return to their perches sooner becuase they are territorial and might lose their territory to other males if they stray too far. Because females are not territorial, they can afford to accompany large animals further from the water to take advantage of the flying insect bounty.
Now, this behavior has not been confirmed in any US dragonfly species, but it is suspected in three: the green darner, wandering glider, and black saddlebags. All three are commonly reported in static and migratory dragonfly swarms in the US, so these are dragonflies that are flying during the dragonfly swarming season. This is also the time of year that those e mails start to come in from people asking why dragonflies are stalking them. I think there’s a connection: the dragonflies in a swarming area are very likely accompanying people, forming little groups around people kicking up little flying insects as they walk.
Tomorrow I’m going to talk about another curious behavior that I haven’t been able to find any information about, but has been reported to me three times now. It’s a bizarre behavior, so I hope you’ll check back!
Literature Cited:
O. Holusa and J. Holusa (2010). “Accompanying” behaviour of Brachythemis leucosticta (Burmeister) in Europe (Anisoptera: Libellulidae) Odonatologica, 39 (1), 63-70
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The Dragonfly Woman 
Wish you a happy new year too, DW! This is indeed a really great observation. I’ve had Libellula lydia follow us for several meters in Ontario, catching the mosquitoes swarming around us. It was a great company to have, but as you noted, they did not follow us over longer distances. Looking forward to read the next!
Oh, excellent! I’m happy to hear from someone who’s had this happen! I can only imagine that having dragonflies flying around you is a good thing, especially if there are mosquitoes involved. :)
Wish you a happy new year too. Great post. This is the kind of post I’d like to read more. Not too technical, yet enough to titillate the brain.
I’ve always wondered, how do entomologists manage to count insects. What methods do they use. Especially because I imagine you would want to be dead accurate about your counts when writing a scientific paper. Perhaps a post about that will also help.
I hope you are planning more scientific posts in the future.
I think with this particular study, the numbers were so low that it was easy to count every individual. However, the means of counting vary from study to study. In one damselfly study I did as an undergrad, I marked off a particular area of the shore of a pond where I was observing damselfly behavior and counted every flight I observed within that area as part of my study. Others will do mark-recapture studies to estimate total numbers and others will use other methods of estimation. Sometimes you can’t count them all and you have to rely on estimations, but so long as you explicitly state in the methods how you counted, then people will be able to understand what you did well enough to make their own conclusions based on your data. And thanks for the idea for a post! It’s not one I’m going to do right away, but it would be a good topic to mull over for a while. And yes, I’m going to do more of these posts in the future. I normally do more of them than I have the last several months, so I want to get back into them.
fascinating post! wishing you the best in 2012.
Thank you so much! I’m glad you liked it!
Thanks for a New Year’s Day science post, wonderful surprise. I’ve been missing seeing & reading much about odes since it got cold. For what its worth, I agree with your theory that the males are too busy with territorial patrols & trying to mate which leads to more females “accompanying” away from water. Have enjoyed reading your blog & will be checking back tomorrow! (@odonataphile)
I’m happy to hear that you think I’m right about the territoriality trumping accompanying in males! I don’t know why the authors didn’t consider it. They didn’t consider a lot of things in my humble opinion, but there was a lot of good stuff in the paper too. I’m glad you enjoyed a winter dragonfly behavior post too. I’ll likely be doing more over the next few months. Gives me an excuse to read about it!
I have a new goal in life: to be followed by a dragonfly.
How is the 2% capture rate measured, and how is it compared to the basal rate of prey capture (that is, while not accompanying?) Is this in terms of how much time they spend following the individual, versus how often they’d be expected to catch at least one prey item during that time period while hanging out in their normal spot by the river?
The 2% capture rate was, so far as I can tell from the not-so-clear methods, measured by counting the number of individuals observed capturing prey while accompanying and then dividing by the total number of accompanying individuals. The authors didn’t do anything to determine what the normal prey capture rate was, so the idea that the dragonflies benefit from accompanying was pure speculation in this case. However, they did say that they only saw insects emerging from the vegetation as they walked a few times on all the walks that they made and that the dragonflies were observed capturing prey every time the prey insects were observed, so they thought it likely that there was a benefit to accompanying as the dragonflies live in an area with little vegetation where flying insects were observed to be scarce. Honestly, there were a lot of things the authors could have done and didn’t and it wasn’t the absolute best paper in the world, but I still think it’s interesting – and leaves a lot of room for someone else to improve upon the study in the future.
Happy New Year. i found you when you were freshly pressed but thought I would wait for things to settle down before popping back in. I live out in the prairies of the midwest and am recovering land from big industrial corn growing, so you can imagine how excited we are when we see ANY insects. This discussion on dragon flies was great. We have plenty of them out here in the summer, we have bees so i keep water plentiful! thank you.. c
Dragonflies are great insects to have around, as are bees, so I hope you continue to see them both as you rehabilitate your land! I would be thrilled to have dragonflies flying around my area during the summer. I live right in the middle of my city, so we get very few dragonflies at my house.
Happy New Year to you too!
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Fascinating! I am still giddy about finding your blog on Freshly Pressed!
I’m glad you liked it! Dragonflies do some really amazing things, as do a lot of other insects.
I was definitely approached by dragonflies occasionally when I was in Australia – the flies where I was working in the Outback were AWFUL, they didn’t bite but they would land on you in large numbers, try to crawl into your eyes, etc., and it was obvious that the dragonflies were attracted by the clouds of flies I, in turn, attracted. In fact, I loved seeing a dragonfly come in and start buzzing around my head because it meant some relief from the stupid, terrible flies. I don’t know that they ever really followed me for any distance, but they would definitely zip around me for a minute or two before taking off again.
How cool! I would LOVE to have dragonflies flying around me during mosquito season! Hate those nasty little flies…
Have thoroughly enjoyed your newsletters! Only experienced the one swarm last year but since connecting with you, I’ve enjoyed the world of dragonflies so much more. Science mixed with the magic of these wonderful creatures! Hope this New Year brings you much more to write about, and share with the rest of us. Cheers!
I’m so happy to hear that! If I inspired even one person to appreciate their dragonflies a little more, then I feel like I’ve really accomplished something here. What a great compliment!
What fascintating behaviour! But a shame that knowing the reason takes away the magic a little. Here in the UK dragonflies seem to do this, too. I’ve had them fly right in front of my eyes and hover there as if they’re looking straight at you. I said hello, of course!
I’m not sure it takes away any of the magic for me as I would be more than thrilled to have a bunch of dragonflies flying around me! Then again, being a scientist who works on insect behaviors, I have a hard time with simply accepting that a behavior exists without trying to explain what it’s for… I’m glad to hear that the UK dragonflies do the accompanying behavior too! I have a feeling that it is a very widespread behavior under certain conditions, but it hasn’t been studied by more than a few people so far. Maybe a good topic for someone to tackle in the future!
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Another reason why females accompanied more than males could be that females, having to produce eggs, have a higher food requirement than males.
Yes, I agree! I think it’s very likely that’s coming into play here too.
Hi DW! I think this is a wonderful post on one of my favourite types of insects! I have definitely been “swarmed” by dragonflies at one particular Ottawa, Ontario trail. This trail is bad for deer flies in June, but I found that when I collected an entourage of deer flies, the dragonflies, particularly Dorocordulia libera and Erythemis simplicicollis, devoured them and made my walks quite tolerable. I thought it was quite amazing to hear the dragonflies’ wings fluttering around my face and to watch them circle me.
Nice! I would love to have that experience! The people who tell me about standing in the middle of dragonfly swarms in their yards tell me the same sorts of things – that the dragonflies eat all the little biting insects flying around them so they don’t get bitten. The dragonfly swarm I saw was going after termites flying out of the grass at a local park, so I’ve yet to actually experience the added pest control benefit of being accompanied or standing in a swarm. I hope I do someday though!
My Grandson and I were in my swimming pool when a dragonfly zoomed in and hovered in front of my Grandson’s face appearing to be starring at him. The dragonfly would then fly from one side of the pool to the other side always with my Grandson in the middle. He would hover at each side of the pool and periodically stopped in front of my Grandson always appearing to be staring in his face. The dragonfly never once hovered by me. Since we did not understand the dragonfly’s action, I teased my Grandson that maybe he should wash his hair more often (he is 11 years old). I told my Grandson we should “google” to see what the drangonfly was doing and found your site very interesting. My Grandson is also one of the people that attracts mosquitos. When he was 4 years old and did not want to come in from play time, we would get him in the house on occasion by telling him the mosquitos we coming out and he would run to get inside the house so he would not get bites. We have also visited a butterfly farm and the butterflies would land on him but never on me.
Interesting! I wrote a blog post about people who attract dragonflies a while back and I’ve been surprised by the number of people who have left comments about that. It seems to be more common than I would have expected, but I still have no idea why some people are more popular than others. It’s so strange! If you’d like to read some of the other comments, just scroll down to the bottom of this post:
https://thedragonflywoman.com/2012/01/02/a-bizarre-behavior/