Lethal libelulasOctober 2nd, 2010 by Jeff Adams
I was enjoying a beverage and good conversation at a friend’s house last weekend when I couldn’t help but interrupt to marvel at a darner dragonfly’s aerobatics in the late afternoon sun. The dragonfly glowed as it flew this way and that, then instantly dropped a foot or two to pluck a tiny glowing speck from the air. Without missing a beat, the aerobat continue its remarkable hunt.
The time for dragonfly watching in 2010 is nearly over. The last dragonflies on the wing tend to peter out in October, but if you’ve got a break and a sunny day, your may still be rewarded on a field trip to your local pond or wetland.
I’ve no evidence for it, but I’d wager adult dragonflies take a back seat only to butterflies as North America’s most popular insects. Many bird watchers are now turning their binoculars toward these denizons of the sky with their pursuits fed by such books as… Dragonflies through Binoculars, Dragonflies of Washington, and our local dragonfly expert’s recent tome Dragonflies and Damselflies of the West. Those who really get into it can visit OdonataCentral to find checklists, maps and even report sightings.
Though not as strikingly colorful, or as likely to be encountered in daily human life, the aquatic dragonfly nymphs arguably exceed their adult forms in their predatory prowess and unique anatomy.
The predatory weapon of a dragonfly nymph, called a labium, brings to my mind the notorious extra terrestrials Alien and Predator. Probably not just by coincidence. As they create terrifying big screen OMD’s (organisms of mass destruction), cinematic monster makers regularly draw inspiration from small products of nature.
Anyway… once prey is within striking distance, this labium is propelled forward by hydrostatic pressure to either spear or grab and scoop prey. The labium then reels the prey in to the mandibles, where it is chomped and swallowed.
Perhaps more intriguing than frightening, is a dragonfly nymph’s butt. A nymph’s rectum actually has three jobs to do. First, as might be expected, it’s the end of the digestive tract and is where poop comes out. However, it also has gills and is water’s port of entry to a specialized respiratory chamber in its abdomen. Finally, the water it draws in to breathe can also be expelled with force as jet propulsion resulting in rapid movement through the water. Pooping, breathing, swimming – not bad for a single part of the anatomy, in an organisms that evolved to something near its modern form 250,000,000 years ago. Enjoy October! JEff
PS – Libelula is Spanish for dragonfly and is no doubt related to Libellula, the Latin genus name for the skimmers – some of our most striking dragonflies.
Jeff Adams is a Washington Sea Grant Marine Water Quality Specialist, affiliated with the University of Washington’s College of the Environment, and based in Bremerton. You can follow his Sea-life blog, email to email@example.com or call at 360-337-4619.