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August 12, 2003

Argiope trifasciata

Watering the garden this evening, Becky found first one, then another, then a third banded garden spider casting their webs over our perennials. The spiders are distinctive: long, tapering legs held in close pairs, elongated body, placid demeanor.

Our banded garden spiders are Argiope trifasciata, common around here. There's a close local cousin, A. aurantia, the black and yellow Argiope: the silver Argiope, A. argentata, lives no further north on the coast than Ventura County.

The spiders are undeniably attractive. But the most distinctive thing about them is their web building. Though the webs in our garden were unfinished and thus lacked them, Argiopes add compelling bright structures of silk - "stabilimenta" - to their webs. Depending on the species, the stabilimenta will resemble angular cursive script, rows of cross-stitchery - "XXXXXXXX" - or my electroencephalograph after my fourth espresso. Bright white, they stand out strongly against the pale silk of the orb, and have brought Argiope the common name "writing spider."

(Philammon was another writer, the son of Apollo, who indulged in an outdoor dalliance with the nymph Argiope. Six to eight weeks later, the story goes, when Argiope brought him a bit of interesting news regarding their impending offspring, Philammon turned his back on her. Rejected, she left Parnassus for Thrace, where their son Thamyris was born. Thamyris was a bard of note, and - again as the myth would tell us - the first homosexual in all Hellas. He had a bad case of the hots for Hyacinth (a.k.a. Hyacinthus, in the Cretan version), a Spartan, who would later die in Thamyris' grandfather's arms, his drops of blood becoming flowers as they touched the ground. Thamyris came to a bad end, as he challenged the muses to a musical contest at Dorium, thousands of years before the devil ever went down to Georgia. He lost and the Muses blinded him. Fundamentalist Hellenists insist he is still being tortured in Hades for his literal hubris.)

Argiope's family line seems more successful in our garden, perhaps because we've planted no hyacinths. I wonder if the spiders will have added stabilimenta by tomorrow. I could wake up to find my yard awash in graduate students. The function of the stabilimentum in the Argiope web (and those of a few related spiders) is the subject of not a little disagreement. They serve to make the webs far more visible, which would seem counterproductive for a stealth hunter. Research shows the stabilimenta reflect an abundance of ultraviolet light, which many pollinating insects see quite well. One persuasive argument holds that the stabilimenta's brightness serves to warn big animals away from the web, while in the UV spectrum, the bright banners are masked by "environmental noise" - UV camouflage, in short. Still, stabilimenta can deter enough prey insects from webs to cut a spider's harvest by a third. It's a confusing issue, and more study of Argiope webs is clearly needed. Maybe I'll call in sick tomorrow.

Posted by Chris Clarke at August 12, 2003 10:46 PM TrackBack URL for this entry:
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decorative line of bighorn petroglyphs