[Odonata-l] black in dragonflies

[Bob Glotzhober]

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

 

 

 

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