|MadSci Network: Zoology|
Dear Christopher Lee:
Hmm... your question has stumped more than one bug person, including me! I'm afraid I can't come up with a definitive response for you, but here are some options.
Interestingly, I was unable to find a description of this black-goop-secreting behavior on any of the numerous web sites dedicated to Odonata (Dragonflies and Damselflies) I explored. So, I called a few entomologists I know, and here's what I learned:
Ed Spevak, Curator in Charge of Insects at the Bronx Zoo/Wildlife Conservation Society, suggested that perhaps your dragonfly friend was reacting to something toxic it had eaten. Dragonflies eat insects, and sometimes their prey are anywhere from distasteful to toxic. Other insects are known to vomit when they eat something that doesn't agree with them, and dragonflies may do the same.
Ed also noted that mantids, particularly Asian green mantids, are known to 'exude black gunk' from between their segments. No one has determined exactly what this gunk is, but some suggest it might be fat. If you've ever gotten to see a mantid, you know they're kind of squishy. This may explain the black gunk=fat theory.
So, the short answer to your question is I don't know. I'll keep your email address on hand in case I find an answer, but in the meantime, please enjoy the web sites devoted to Dragonflies and Damselflies listed below.
I feel a need to include some of the interesting tidbits I found, just
because I'm sorry I couldn't provide a clear answer. Here's something fun:
From Green Darner Dragonfly for Michigan's State Insect:
"There are several interesting superstitions about dragonflies. They have been nicknamed "devil's darning needles" by people who believed they flew around sewing up the eyes or ears of naughty boys (yes they have long, needle-like bodies, but they lack stingers and cannot bite people); they've been called "horse-stingers" by people who saw them darting at horses (only to catch the horseflies that were trying to bite the horses); to others they are known as "snake-doctors" and are supposed to guard snakes (they do inhabit damp areas were snakes often abound, but they have no association with these reptiles). They do, however, have one nickname that is an accurate description for their best attribute; they are fondly referred to as "mosquitohawks" because of their big appetite for these pesky biting insects! "
Check out the following:
Beginner's Guide to Dragonflies -- great starting point, lots of links
Biology of Dragonflies and Damselflies by Ron Lyons. His extended introduction is particularly good. So good that I emailed him to see if he knew about black goop, and haven't heard from him.
Thanks for your interest, and keep watching that clothesline!
Ruth Allard Conservation Biologist American Zoo and Aquarium Association
Try the links in the MadSci Library for more information on Zoology.