Friday, November 20, 2015


I lucked out when I took this photo of an orb web; the individual strands of silk illuminated by the early morning sunlight. Normally an orb web is practically invisible. That’s why they are such effective traps.

But there’s one group of orb weavers—the writing spiders—that decorate their creations with highly visible patterns. These conspicuous silk structures are called “stabilimenta” or singular: stabilimentum, a great word to drop into any casual conversation.

Why go to so much trouble making a normally invisible web visible?

Why indeed?

Theories vary. And the weavers themselves are mute on the topic. Writing spiders like the ones in the genus Argiope tend to be brightly colored and they often position themselves in the center of the web. The stabilimenta may help camouflage the orb-weaver or make them look larger. The patterns also reflect UV light, which may serve as a lure to possible prey. Plus, the pattern may help keep birds from flying through the web, tearing it down.


Rikki Hall said...

I'm definitely in the camouflage camp regarding these structures. Notable is the fact that Argiope are among the spiders that vibrate their web when danger nears, turning themselves into a blur in the center of the web. The stablimentum surely enhances the disorienting effect of this trick.

Also, look for the webs of immature Argiope next year. They emerge fairly late, after meadows have become dense and tall, and build closer to the ground than adults do. These smaller, more vulnerable spiderlings build an oval stablimentum that matches their legspan and sit right in the center. I suspect this feature is more critical to younger spiders and something of a remnant behavior in mature spiders.

Patricia Lichen said...

I'm in the stabilimentum as lure camp, but I have to admit it's been a while since I looked into this, so I could be swayed.

Under this theory, flying insects are lured into the web--the spider isn't just passively waiting, she's actively attracting her prey. The zig zags reflect ultraviolet light, and the patterns mimic ultraviolet markings on flower petals that guide insects to nectar (like landing lights on an airport runway).

Regardless, great photo (as always!), SL!

Marie said...

I often wondered why certain spiders made such designs in their webs. I thought it might have something to do with repair, but it was wonderful to read here about the possible real reasons. Very interesting post!