[Odonata-l] [se-odonata] what a difference a day makes

[Chris Hill]

On Sep 17, 2006, at 7:02 PM, SL Brown wrote:

>  The procession stretched in both
> directions (flying along the beach) as far as my eyes could see, went
> from near the water's edge at least 100 feet back to the line of
> houses, and my estimate on density was 1 ode per 2' x 2' x 2' of
> aerial space all the way up to Wandering Glider flight height. The
> procession was fully in progress when I arrived at about 6:30 and
> continued after biting flies made me leave at 7:15. Anyone care to do
> the math on that? ;)
Can't resist that challenge:

100' wide x 50' high* x 10mph** x 45min x 1dragonfly per 8 cubic feet  
= 24,750,000

25 million dragonflies.

*is 50' what you mean by Wandering Glider flight height?
** does 10mph seem a reasonable traveling speed for migrating  
dragonflies in still air?

Next time we need video as well as still pictures so we can check  
some of the estimates (flight speed, density) that went into the math  
above.  But no matter how imprecise the above, it's a fun exercise.   
I'm probably being generous with flight speed, but I know I can't  
outrun a migrating green darner, so my error not more than a factor  
of two (I can run 5mph, even in my middle-aged decrepitude).

Chris


Christopher E. Hill
Biology Department
Coastal Carolina University
Conway, SC 29528-1954
chill AT coastal.edu
http://ww2.coastal.edu/chill/chill.htm