Driving home from our cottage yesterday, I noticed a few trees had
grayish/blackish smoke drifting only from the top of the trees.  I
shrugged it off,  thought maybe I was seeing things. A few miles
later,  I saw it again, only now it affected every tree for miles
(both deciduous and evergreens), I asked my girlfreind if she too saw
it. She did.
What is it?

Let me provide the details that may help:

We were in Michigan roughly 2 hrs. north of Detroit.  (rural
community)

It was dusk, mild-cool weather.  (mid 50s, to lo 60's)

All "smoke" was roughly 2-3 feet long. 

It was always drifting* due north, from the very top of the tree. 
Parallel to the ground, perpendicular to the tree.
(*I say drifting although it looked like it was hanging, not moving).

Visual suggestions:
Like a thin gray stocking blowing in the wind, or a very concentrated
group of gnats.
(however i'm almost positive it wasn't gnats.)

Thanks!

Wow 028261-ga, 

I witnessed the exact same thing last year!  I was walking alongside a
road early one morning, and looked across a field and saw the top of a
tree “smoking” just as you described. The closer I looked, the more
trees I noticed doing the same thing. Some evergreen, some deciduous,
and all sending a spume of 4-6 ft “smoke” in the same direction --west
in my case.  The tree heights ranged from about 12 feet to upwards of
30 feet.

Fortunately, I wasn’t zooming by on the interstate, I was on foot. So
I crossed the street, climbed a fence and went to investigate. Two
lone deciduous trees (about the size and shape of an apple tree), both
smoking, stood in the middle of the field so I headed for them. When I
got maybe 100 feet away I could hear that the “smoke” was buzzing!

As I got even nearer I could make out that they were indeed insects,
but I wasn’t close enough to get a real sense of size or markings. It
was odd because, although they were flying, they weren’t “going”
anywhere. My sense is that they were flying in place by flying into
the wind and the whole mass of them just drifted up and down with the
wind shifts.

The good news is that I did identify the “smoke” as a swarm of
insects. The bad news is that I then got visions of Africanized killer
bees in my head. Ok, I’m in Canada and I know better, but still,
Crocodile Hunter I am not. I decided to retreat.  It occurred to me
that if for some reason these critters decided to attack en masse, I
had no means of escape. So, I never did get close enough to make an
accurate ID.

Of course I went home and promptly did an internet search (as I’ve
done again for you today) but found little definitive information on
exactly what insect I saw.

But, today, in searching more thoroughly,  I did find a description of
the behaviour as it applies to several other insects that are endemic
to our latitudes (Upper Michigan, lower Ontario) ----


“Male mosquitoes, black flies, and biting midges tend to assemble in
the evening, often in swarms. They usually remain hovering or flying
back and forth over or beside some prominent object, the "swarm
marker." When the swarm is large, the noise of the wing beats may be
audible for some distance.”

http://res2.agr.ca/ecorc/program2/entomology/biting_flies/english/flies05e.html



“The inadequacy of passive, wind-driven traps in assessing the aerial
insects of Delta Marsh”  by  Stephen Ellis - Environmental Science
Program, University of Manitoba


 “ In the late evening (and to lesser extent at sunrise), large masses
of males, some with millions of individuals, form in relation to some
conspicuous element of the landscape … the Chironomus [midge] swarms
seem to locate themselves above such landmarks as the summer road, the
beach or even a conspicuous tree. These swarms remain a relatively
constant distance from the swarm marker, adjusting height and position
with changing wind conditions. Chironomid swarms are
characteristically columnar in form, as exemplified by the Chironomus
at Delta Marsh.”

UNIVERSITY OF MANITOBA – DELTA MARSH REPORT 1996
http://www.umanitoba.ca/faculties/science/delta_marsh/reports/1996/ellis.pdf



“In most species of black flies males assemble into airborne swarms
over an object called a 'swarm marker'. The tops of bushes, large
stream side boulders, or large branches of isolated trees are just
some of the myriad objects that can serve this function.”

INSECTS OF HALIBURTON COUNTY - ONTARIO –
http://www.haliburtonhighway.com/haliburtonhighway/insects_of_haliburton_county.htm


So that should solve the Mystery of the Smoking Trees!  

I’m glad you asked the question because I gave up on the search myself
last year after finding nothing online. Your question gave me the
impetus to go after it again and not quit until I found an answer. And
next time I see the “smoke” I’m going to traipse right in a get a good
look at insects that make it up.

Thanks for asking a great question!

-K~

search terms:

I searched everything from “bee swarm” to “insect migration”  and
every other combination of terms I could find. It wasn’t until I
accidentally came across the term “swarm marker” that I found what we
were looking for.

Oustanding! and quick too!

KS' answer is almost certainly correct, given the season and
conditions.  Yesterday winds were light -- under 10 knots at dusk
according to the Flint, MI weather reporting station.

A 2nd possibility is that an inversion layer, common in calm air, was
holding smoke from houses or campfires down at treetop level.  The
smoke would have streamed to the north -- as what winds were present
yesterday were out of the south.  (The same winds would carry insects
north as well.)

Inversion layers like this are common in Seattle, holding smoke down
in the atmosphere so that fireplaces can't even be used.  Here's an
illustration of how air layers trap (and flatten) smoke or air
pollution:
http://www.fellwalk.co.uk/page54.htm

Note the comments on fall temperature inversions, common in the fall
with high pressure systems.

Best regards,

Omnivorous-GA

Thanks for all your help! 

This is a great service... next time I think I'm going crazy, I'll check here first!

Thanks for all your help! 

This is a great service... next time I think I'm going crazy, I'll check here first!