[Next Door Nature] Skywriter

Editor’s note: This article originally appeared on www.nextdoornature.org. Copyright 2012 Kieran Lindsey. To subscribe to this blog, visit www.nextdoornature.org.

The writing spider has a signature web that makes the species easy to identify. (Photo: Alan Howell © 2012 Star Path Images)

Not on purpose, mind you. My aerobic exertions sometimes move from an indoor treadmill to the outdoors and a tangle of pathways that wrap around the surrounding neighborhoods. My earbuds wedged firmly in place, the volume on my iPod turned up loud enough for the bass to create some nice cranial reverb, I walked toward the road with my head already in the clouds.

I returned to Earth in a hurry, though, when I flew through a spider web strung between a pedestrian crossing sign and a maple branch. Come to think of it, the impromptu Elaine Benes dance moves inspired by contact with a cobweb made for a pretty good workout. Just not the one I’d planned.

The impact caused some turbulence in other plans as well — specifically, those of the writing spider (Argiope aurantia) I was destined to meet. All I had to do was pull wisps of skywriting off my face, hair and arms, and I was good to go. Charlotte faced a bigger clean up.

When people write in the sky, they use small, agile planes and a device that injects oil into the hot exhaust manifold, creating plumes of dense white smoke. It’s an inherently wasteful process and the results are ephemeral, to put it mildly; the message begins to blur within minutes. Spider webs are longer lasting — about 24 hours or so — but my eight-legged barnstormer is heavy into recycling. She ate yesterday’s draft last night and used it as the raw material for today’s composition. She does this nearly every night, and it’s a task that takes hours to complete. Now, thanks to me, instead of resting in her hammock all day waiting for dinner to be delivered, she’ll be busy scribbling for the second time in 12 hours.

Her nom de plume comes from a set of silky zigzags resembling text that she inscribes through the middle of a circular insect sieve up to 2 feet in diameter. Known as the stabilimentum, because it was originally thought to stabilize the structure (Latin just makes everything sound so much more consequential, doesn’t it?) her writing now gets mixed reviews. Some folks think insects are attracted to the bright lacing, the way they would be drawn to a flame or a porch light. Still others believe using a bold white font alerts large non-prey creatures to the presence of the web so they can avoid colliding with it. I realize I’m only one data point, but I’d like to suggest an exception to that second hypothesis: It doesn’t seem to work all that well for bipedal mammals.

These highly visible orb weavers can’t see very well themselves, but they are attuned to air currents and web vibrations. The male (0.2-0.35 inches/5-9 mm) goes so far as to communicate with the much larger object of his affection (0.75-1.1 inches/19-28 mm) by plucking and strumming the strands of her web. This tells her the caller is a fella, not a feast. Then again, he may be both. Foellmer and Fairbairn (2003) report that A. aurantia males “invariably” die within seconds of copulating, not because the female kills them, but as a form of sex-triggered suicide (the lengths some men will go to avoid post-coital cuddling!).

Skywriting at 7,000 to 14,000 feet aims to grab the attention of spectators on the ground, usually to sell them something. When it’s done at 2 to 8 feet of elevation, it’s intended to capture and hold groceries — in the form of aphids, mosquitoes, wasps, bees, crickets, grasshoppers, and even dragon- and damselflies — long enough to bag ’em up.

An insect intersects with a web and the resident spider rushes to its side before an escape can occur. What happens next is gruesome, but that’s a bug’s life for you: a quick bite delivers paralyzing venom and begins to turn innards into soup (the substance is harmless to humans, by the way). Then, almost faster than the blink of an eye, spider feet are juggling the hapless intruder until it’s spinning like something out of Cirque du Soleil. When the stunt is complete she’s got a silk-wrapped burrito. Convenient, portable and ready-to-eat…the perfect snack for a calligrapher who writes and walks on air.

Dr. Kieran Lindsey loves looking for wild things in all the wrong places…so she became an urban wildlife biologist. Her quest to entice others to share this passion led to flirtations with (gasp!) the media as a columnist for the Houston Chronicle newspaper, as writer-producer-host of KUNM-FM’s Wild Things, as co-producer of an Emmy-winning wildlife documentary, and at her Next-Door Nature blog. Kieran also has way too much fun as the official Animal-Vehicle Biologist for NPR’s Car Talk, and she isn’t ashamed to admit it. Read her blog at www.nextdoornature.org. Contact her at klindsey@giemedia.com.