by Matthew Cobb
The UK has been basking in an unusually gorgeous summer for the last 10 days or so. Tomorrow the weather breaks with some welcome thunder storms predicted. So in case I don’t get another chance this year, I have just had my tea in our small garden – fromage de chèvre and salad, with a decent Bordeaux Supérieur from our local French épicérie, chez Ludo on Beech Road in south Manchester.
I was getting gently sizzled in the evening sun, revelling in the wine and the warmth and the smell of the sweet peas:
Then I noticed 5-7 dancing midges above my (empty) plate. The tiny flies were moving up and down, occasionally zooming into contact with each other, then resuming the dance. Every now and again the wind would blow them away and they’d take a few seconds to reconstitute their dance, in the same place.
This intrigued me. These dances are thought to be composed of male midges that are forming a ‘lek’ – a kind of dance floor where the guys strut their stuff. Female midges who are up for it will dive through the melée and find a male that suits their needs. The midges zooming in on each other will have been males who were checking out the sex/availability of another midge (probably through their cuticular hydrocarbons – sticky compounds on the outside of many arthropods, which both Jerry and I have studied).
So who do the ladies choose? In a 2003 paper entitled ‘Mating in a viscous universe: the race is to the agile, not to the swift’, Crompton and coworkers concluded that bigger is not better in the midge world: ‘the hypothesis that small males gain their mating advantage through acrobatic superiority is consistent with the observations reported here’.
But I was intrigued by where the males were dancing. They were always over my plate, about 30 cm above the surface. I tried to take a picture of this, but n’est pas Alex Wild qui le veut (not everyone can be Alex Wild), and you can’t see the midges at all. But you can see the plate.
(The midges were slightly to the right of the chair, against the greenery. Honest)
And that turned out to be the key thing. If I moved the plate, the midges moved with it, dancing as they went. If I raised the plate, they moved too, keeping the same height. I called my daughter Lauren down, dragging her away from her computer (“Oh Dad, what is it?”), and she was equally amazed. It was very weird. It was like a magnet, she said. And it was. Wherever we moved the plate, the midges followed, completely unaware that they were being shifted around the garden.
I remember noticing this years ago, when I was in a garden and found a column of midges dancing over my head. I moved and the midges moved. I assumed this was something to do with heat/smell. Maybe this was to do with reflected light, or the smell of cheese or… what?
What are the males after? Is there any instrinsic advantage to occupying a space above a plate (maybe they think it’s a pool of water, so the females can lay their eggs in there?) or is it just some place where they can show off?
I’ve had a quick look online on Web of Science and on Google, and can’t find any answers. Do any readers have any ideas?
Ollie the cat (who scratched Jerry’s nose when he visited a while back) came to inspect what was going on, but he didn’t have any answers:
Reference:
Haven’t a clue…so I’m subscribing in the hopes that somebody else does.
b&
Just guessing, but maybe this is a clue:
So the males prefer to dance against an expanse of contrasting background as seen from above.
I assume Matthew to be bald then…
No idea as to the midge behaviour, but Ollie is a magnificent wee beastie. Please give him (?) some fuss from me please.
I witnessed a similar thing on a Summmer’s day a few years ago: whilst driving along a fenced road, I noticed huge clouds of bugs (no idea what they were) concentrated every few yards above the fence-posts. I couldn’t think why they would gather in this way. In this case it couldn’t have been the light, but maybe the heat had something to do with it…?
Great observation! Midge swarm location varies from species to species, with some species particularly fond of height-dependent landmarks, while others choose to meet over top of distinctive patterns. Seeing that you were able to lead them around with the plate, I suspect your fly friends were reacting to the brightly coloured plate set among the browns, greens & other earth tones of your patio. Whether they’re sensing the actual colour of the plate, or just the increased light reflecting off the glazed surface, I’m not sure. Either way, the plate acts like a beacon, helping both males and females realize where the party is at.
I wrote about a much larger swarm that a UK photographer found hovering above a country road on my blog, including some spectacular photos the photographer let me share. There’s also some more info on how selective swarm location may act as a reproductive barrier for closely related species.
For a good, easy to read primer on swarm behaviour of UK midges, check out this paper published in 1945 – On The Mating Swarms of Certain Chironomidae (Diptera) by N.H.E. Gibson.
Is this something also seen in ceratopogonidae? I was wondering whether the different swarm behaviour between closely related species also occurs in biting midges. Has anyone tested the hypothesis of reproductive barrier?
Your blog article tangentially raises another question for me: How on earth does one pin a midge? 🙂
See figure 5 here
http://www1.extension.umn.edu/youth/mn4-H/projects/environment/entomology/collecting-and-preserving-insects/
I too have noticed the fact that the swarm will follow you around, hovering over your head(I am not bald) but not seen the plate effect before. Also a blast from the past, re comment by Morgan Jackson, Noel Gibson taught me entomology at Leeds in the early 1970s and incidentally sparked my interest in aphids ;-), despite the midge paper!
“I am not bald” – that’s right, rub it in!
🙁
Midges will commonly form these mating swarms over a landmark. It is how they ‘find each other’ in a big world. I will see them swarming over fence posts, for example, spaced out at intervals over each post.
Think I may have spent to long in Scotland and other parts where the females feast on anything not protected by ten layers of mesh but my thoughts immediately turned to how it could be used as a defence.
Let me know if you find out – please!
They’d breed around it. I’ve never met a midge defence that worked – other than closing up the tent and lighting up a stove, candle, or doobie.
Then again, I’m one of the people who generally only has to put up with the creeping sensations of the millions on my skin ; if they bite, they don’t seem to do much damage. I’ve seen (and avoided) some of those poor unfortunates who have “midge magnet” painted on them in midge-attracting odour-paint. Grim for them.
I attract flies, mosquitoes not so much. That is the better deal in most cases, since you drag around midge-proof nets on hikes in Sweden anyway but mosquitoes are everywhere some years.
The only time I get pissed is when I’m the first to become aware of the horse-flies arriving at the beach.
For “sizzled” read “sozzled” 🙂
The comments above about swarming over fence posts & bushes…
I wonder if this has more to do with air movement than a visual signal? Perhaps locations like that are prone to thermal updrafts within inches of the object This surface effect might assist a midge by creating a pocket that resists any breeze tending to throw midges off station while they’re busy dancing. There is always a region of dead air near objects ~ the wind speed grades down to zero, but this is very close to the object surface…
Fruit flys in Melbourne (Aust) all gather under a hanging thing, tree branches, or the ceiling fan in our family room. They fly round in squares having the occassional quick tussle with each other, waiting for a female to wander past.
I guess the key is that they all know where to find each other.
It’s just a guess but maybe the males stand out more clearly when flying over a white plate. If they want to be seen by females this would make sense…
A sheet of white paper held up by Lauren behind the midges might have done the trick in a photograph!
sub
I read the headline as “The Case of the Dancing Midgets”. I saw the wine and the flower and thought Jerry had been tripping on a combo of alcohol and some hallucinogenic plant.
I think it’s time I broke down and got bifocals.
Looking at the pictures in full resolution and inspecting each centimeter I couldn’t find anything definitive. Then I saw one or was it a smidge, not a midge but a smudge on my monitor? Nope, for it turned out to be a bit of jewelry on Ollie’s eyebrow.
Matthew,
The porcelain plate may polarize reflected light and provide a distinctive visual landmark for the lekking male midges and their ladies. In the real world a puddle of water might produce the same effect.
Different insects use different landmarks, perhaps as an adaptation against multi-species traffic jams.
I attract midges which dance about in a sort of column over my head – they also bite sometimes. I think it is because I have bleached blonde hair! But biting things all bite me and not my partner. Not fair at all.