Saturday, October 28, 2017

Lumpy, bumpy, orange spider

I almost stepped on her. A fat, orange spider was parked right beside my work chair; when I turned to go for a coffee, my foot missed her by a couple of inches. She didn't even move.

She barely bothered to react when I put the camera down a few inches from her eyes. Trusting soul!

I took more photos. She turned her back on me. I don't think she liked the flash.

"Knees up, Mother Orange!"

I think she's a Marbled Orbweaver, Araneus marmoreus, an extremely variable species, but the eye placement is right, and the pattern of legs and body fits. And these spiders hate the light.

An interesting exchange on BugGuide:

"While focusing I noted that the round protruberances on her back were pulsating. Are these respiratory?..."
"Yes! ... I've noticed the pulsating as well. I believe it is a defense mechanism. ... It could be that they are trying to produce silk so that they can 'web' away from me.
But as I originally said, I think it's just a defense mechanism. Perhaps to make them look larger to predators."
… Nikole Loomis (Bush Cricket and Buckeye Lover)

When I was done, I shooed her off towards a corner, where she could safely lay in wait for the next passing harvestman. I went for the coffee, finally. When I came back, there she was, sitting patiently beside my chair again. Time to deport her!

In an Ikea glass, waiting to be moved.

I put her outside, in the rain. And it turned out that was a lucky move. That white powder on her pedipalps in the first photo? I realized that it was the remains of some diatomaceous earth I'd spread around in the hot days of last summer, when we had been invaded by fleas. I had vacuumed it since, of course, but there's a bit still hanging around in the back of my closet. And it's a spider killer, too.

Although it feels much like talcum powder to humans, diatomaceous earth is actually jagged, and when spiders walk across the powder, it begins to jab and cut into their hard exoskeleton. According to the Oregon State University, the wounds created by the jagged diatomaceous earth cause the spiders to desiccate, or lose all of the liquids and oils from their bodies. This desiccation eventually leads to death. (From sfgate)

It's a slow killer. It takes a spider two days or more to dry out and die. However, if it rains, or if the ambient humidity is high (like anywhere outside here, these days) the diatomaceous earth slides off, and the spider lives.

And fortunately, "Mother Orange" had collected it on her pedipalps and some of her feet; most of her skin was clean. I think she'll live.


  1. Jeepers! Isn't diatomaceous earth a major component of kitty litter (aka shit grit Chez Dinahmow)? It might dessicate spiders, but I can confirm that ants (some species)are not bothered!

    1. I think the degree of pulverization matters. The insecticide diatomaceous earth is so fine it flies into the air with the least movement.

  2. There is a beautiful web on our porch, I think it is an orb weaver but I haven't seen the spider yet. - Margy

  3. The shriveled shape of her abdomen makes me suspect that she's laid her eggs, and probably would've died soon after anyways. Araneus spiders don't typically crawl along the floor anyway, so I doubt the diatomaceous earth is what lead to her languid state (though it probably didn't help).

    1. Yes. I'm glad I put her out in the rain. And later I gave another spider a good bath. And I no longer use diatomaceous earth.


I'm having to moderate all comments because Blogger seems to have a problem notifying me. Sorry about that. I will review them several times daily, though, until this issue is fixed.

Also, I have word verification on, because I found out that not only do I get spam without it, but it gets passed on to anyone commenting in that thread. Not cool!

Powered By Blogger