What makes flying insects swarm?

I bet most people with inquisitive minds take the time now and then to observe natural phenomina around them. Here's one such observation I've made over and over. Small insects the size of large gnats frequently swarm in my yard in summer. They come together in groups and in certain spots. The odd thing is that these spots can remain stationary for weeks. The regions where they swarm appear to be in the shape of a cylinder standing on one end, about a foot wide and extending as high as 6 or 7 feet. It's so obvious cause when a breeze blows the bugs off the spot, their swarming behavior ceases. Then they gradually find their way back to the spot. I've even noticed that a single bug flies normally until it enters one of the zones, then it's flight changes to small tight circles.
These zones migrate around sometimes. I cannot detect any difference between the zones and any other spot. Are the bugs reacting to some field phenomenon? Any ideas?

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I've found that gnats often swam directly above areas where the ground is lighter in color. The only thing I could think of is that areas with dead biomater (good for laying eggs) is often lighter in color than the surrounding medium. I think they swarm for reproduction reasons, anyway, I'm not sure.

I first noticed the color thing while hiking. There would be a huge open feild, and a column of swarming gnats. If I went over to investigate, I found that the gnats were right over a large white stone or electrical serice box or something noticable lighter in hue than the surrounding area.

 

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As I said, I've noticed no difference in the "swarm zones" and the rest, just green grass. I used a stick to mark one zone to see if it moved the next day; it didn't.

I don't give these critters credit for much free thought (maybe they don't give me much either!). I think they mostly respond to stimuli. What occurs to me is that perhaps they sense some field anomoly like electromagnetic. To watch them is like watching the effects of an invisible field like magnetism. Again, I've watched the first few bugs returning to a zone; they change their flight pattern when entering the zone. Doesn't look like their reacting to each other. Go figure.

 

Its like the groups of fishes that look like a big living wave..

To evade predators

To coordenate migration seasons, and areas were there is more
food, if they stick together they will find the best resources..

About the insects its pretty much the same thing, and these
swarming animals have a kind of "6th sense" that permits them
to be syncronized with the rest of the group with split second reactions that amaze us... they could all have some kind of magnetic "radar" to avoid crashing into another, and detecting the presence of each other and swarm formations

 

All the swarming insects I have witnessed have not show this type of localization behavior, but I live on the other side of the world.. river-wind most probably has the answer. Most insects have very sensitive eyes that are well adapted to finding there way to and from geographic locations. Why they swam at specific points is conjecture but the best way to find out is to experiment.

Instead of just marking the swarms location, start changing the visual appearance of the scene.Add bright object, mats whatever. See if you can relocate the swarm.

As far as I know insects don't notice electrical/magnetic fields.

 

I think I've seen what you are talking about at beaches and swamps a few times. Its not like swarming as they fly through an area they actually hover in a visually distinguishable shape and stay in one spot.
Actually I've seen it on a football field a few times when I was a kid as well. There was one feild with one area where they would be every week and you wouldn't see them untill you ran through them and got bugs all over your face.
I never thought about it but yeah, what the hell are they doing?
It seems like they would be sitting ducks for predators like bats and so on.

 

The way it looked to me is the bugs fly more or less straight (or in large arcs) in most areas you see them. The reason they swarm in one spot is because their flight paths change when they get there from straight flight to moving in small circles. Once each critter hits the spot they are "stuck" there flying in circles. I've even seen the first one or two return to a zone and change the way they fly. The zone appears to trap these bugs one by one till there's enough to call it a swarm.
It may be reaching, but maybe these little "sensors" can detect things we don't even know to look for.

 

Most interesting!

This needs further investigation....

Perhaps we could do some field experiments of our own, for instance by identifying swarm hotspots and shove a bright blanket on that spot, give them time to acustom to the balnket and after a while drive the swarm away and move the blanket 10 meters or so, see if the swarm will return to the original hotspot, or to the new spot, associated with the blanket


Also, the remark about light spots in the landscape, might create different Infrared temperature zones, cause the sunlight is reflected in another way. I don't know if a higher temperature will create favorable thermics or something so that the bugs can do away with spending less energy to keep in flight ?

All in all the study Swarming behaviour is very intriguing...

 

Natural:

Interesting. Perhaps there is something chemically attractive about such spots?

Try a little information theory:

Bug 1 finds a spot that is, for whatever reason, good.
Bug 2 follows bug one. Bug 3 follows 2.

Common herd behaviour - you see it with zebras. Zebra one sees a lion and bolts - z2 follows z1 - if z6 sees the behaviour of z2, z6 runs, copied by z7.

Very quickly, the behaviour (running away) has spread through the whole herd.

Basically, the group acts as a whole because it is very sensitive to the behaviour of individuals.

 

In the mention of color, it has long been known that dirt dobbers and wasps do not make nests under porch roofs that are painted sky blue. I believe the reason for this is the insects think it is the sky and therefor not a place to build a nest.

Surely survival factors into this behavior of swarming. It might be that be swarming it increases the survival factor of each individual insect by being able to hide with in the mass of others.

 

wet1:

And to confuse predators - witness the way fish "swarm".

But does that explain why they form in such strange configurations? The gnats around here swarm in straight lines. Also along sidewalks - like someone mentioned, they're attracted to light things. But they don't swarm above the sidewalk per se, more in a straight line right beside it.

 

How about this explanation?
Seems reasonable to me
http://www.straightdope.com/classics/a2_069a.html
I've noticed that they sometimes follow anybody in a light colured shirt, so the visual explanation is more likely than any magnetic or chemical cues.

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