[Odonata-l] black in dragonflies

[Nick and Ailsa Donnelly]

As an additional note, the more northern members of widespread species
commonly have more extensive black than their more temperate cousins.  An
example that struck me at the time was Enallagma ebrium, which in Northern
Quebec is so black as to cause at least one person (not me) to think it
might be a new species. (not me)
 
Nick Donnelly

  _____  

From: odonata-l-bounces at listhost.ups.edu
[mailto:odonata-l-bounces at listhost.ups.edu] On Behalf Of Bob Glotzhober
Sent: Tuesday, December 04, 2007 1:38 PM
To: Odonata List Server
Subject: [Odonata-l] black in dragonflies



I am looking for data, opinions, thoughts and ideas on why so many
dragonflies have black as a major color. This initially hit me last summer
when a couple of us locally were working with 3 plus species of Macromia on
the Big Darby Creek near Columbus. Since then, I've been invited to talk to
a bunch of folks as a part of our state's wildlife diversity conference -
and the entire conference theme is "Back in Black".  Obviously, an emphasis
will be around the resurgence of black bears in Ohio, but also other "black"
wildlife including cormorants, black vultures, the (melanistic) Lake Erie
Water snake, and others - including black dragonflies.

 

While my emphasis will be on the diversity of such critters and their
ecology, I want to spend a little time discussing the thought of why so many
are black. To launch things (my apologies to Tom) I am inserting a
communication from Dr. Tom Schultz at Denizen, who has worked on colors in
Odonata before. This is a basic good start - and maybe it will stimulate
some further thought and discussion within this group. I eagerly await to
hear not only hard data but off-the-wall theories as well. 

 

Here is Tom's correspondence:

"Bob,

I have given this a little bit of thought.  The combination of yellow and
black is as conspicuous as any Odonate coloration can be, especially if the
visual system of the insect is trichromatic with sensitivities to UV, blue
and green (like bees).  The striping provides important contrast that
enhances detestability; consider the difference in how C. erronea looks
compared to S. linearis when each patrols the same shaded stream.  In dark
forest understory black and yellow would be the color pattern of choice. In
light flecks, yellow is a conspicuous color  because it reflects the
filtered green-yellow light without matching the green background. However,
when flying in and out of light flecks the broken pattern of Cordulegaster
should make it hard to detect.    

 

The eyes may be part of the color pattern that  these dragonflies use to
attract mates or identify themselves, but they should also boost the
reception of the wavelengths they reflect (e.g. green).  No research has
really been done on the roles of color in odonate eyes, but it is a
reasonable guess that the emerald green eyes may function like a tapetum in
vertebrates.  

 

There are only three studies using electrophysiology to determine the color
vision of an odonate species.  Two bluets are know to have receptors for UV,
blue and green.  It has been shown that one red libellulid species has an
additional  red photoreceptor.

  

Tom"

 

Bob Glotzhober

 

 

====================

Robert C. Glotzhober             614/ 297-2633

Senior Curator, Natural History         bglotzhober at ohiohistory.org

Ohio Historical Society         Fax: 614/ 297-2546

1982 Velma Avenue

Columbus, Ohio  43211-2497

 

Visit the website of the Ohio Historical Society at:

  www.ohiohistory.org and check out our online collections catalog.

See or purchase Dragonflies and Damselflies of Ohio or the Cedar Bog
Symposium II at OHS's new E-Store:  http://www.ohiohistorystore.com/ 

Visit the Ohio Odonata website at:
http://www.marietta.edu/~odonata/index.html

 

 

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailweb.ups.edu/pipermail/odonata-l/attachments/20071205/8975712d/attachment.html