Mind the Rock Snot

by Jennifer Frazer on August 17, 2010

Creative Commons Thorney¿?

Fly fisher(wo)men everywhere are mourning the loss of a cherished piece of equipment: their felt-soled waders. All too often now, clinging to the felt fibers are the tenacious strands of Didymosphenia geminata (did-em-o-sfeen’-ee-a jem-i-na’-ta), or, for the rest of us, rock snot.

The stuff looks like pre-owned toilet paper and apparently feels like wet cotton, and it’s slowly taking over the freshwater streams of the temperate world, smothering fish, insects, and other aquatic life. It spreads by hitchhiking on the gear of flyfishers, challenging slime molds, dandelions, and jellyfish for the non-human Plans for World Domination Cup. You can read all the gory details in New York Times articles here and here. But hidden inside that slimy brown mass is a work of remarkable beauty.


With the lines of a Stradivarius and the detailing of a Fabergé egg, this baby is a microscopic work of art. If only its macroscopic manifestations could be so beautiful. As you may have guessed, it is a diatom (as covered here), a microscopic glass house (literally (littorally?) made of silicon dioxide) enclosing a little photosynthesizing alga.

At left you see two interesting features: The two long slits, or raphes, through which the diatom can secrete mucilage (aka slime) with which it slides over surfaces, and the porefield, through which it can secrete a mucopolysaccharide (aka slime) stalk that attaches it to a surface. The secretion and aggregation of these stalks is what causes the brown mess of rock snot, not the beautiful fiddle-like head.

In beauty, destruction. In destruction, beauty. This particular destruction brought to you by the otherwise largely upstanding diatoms, conveniently located in this sector of the tree of life. For all the scientific, er, dirt, on rock snot, including a beautiful scanning electron micrograph of the trouble-causing stalks, check out this EPA White Paper.

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{ 8 comments… read them below or add one }

Amy August 18, 2010 at 8:38 am

Unrelated: I feel very strongly that littoral should be pronounced with the emphasis on the middle syllable (lit-tor’-al instead of lit’-t[shwa]r-al). I was shocked and appalled to find out that this was not the case.

That is all.

other amy August 18, 2010 at 6:09 pm
Penelope August 25, 2010 at 6:55 pm

Hi Jennifer, I’ve followed Claire’s lead to your terrific site. I opened the ‘White Paper’ link at the end of the Rock Snot article, thinking that someone might have taken seriously my idle thought on seeing didymo dried and bleached on the Waitaki River bed: it could make great ‘white paper’ — but would every page embody as much potential damage as a felt-soled fisherman’s wader?

Jennifer Frazer August 26, 2010 at 10:22 pm

That depends on who’s using it! : ) Sorry it was not the “white paper” you had in mind . . .

Ben September 4, 2010 at 1:21 pm

That 4th paragraph is now one of my all-time favorite pieces of English prose. Thanks, Jen!

Jennifer Frazer September 4, 2010 at 4:39 pm

Thank you, Ben! That’s extremely flattering since you were one of this stylist’s key influences! : ) I have not forgotten about your Chicago travel offer — soon, I hope!

Lissa Harris September 17, 2010 at 4:27 pm

Hi Jennifer — checking out your marvelous blog after a long absence, I came across this post, and had to feature it on our Catskills-area news website.


I’ve got a big, big love for the underappreciated creatures of the world. This one’s a tough one to love, though. Didymo is the terror of our waterways around here.

But like they say, “all God’s critters got a place in the choir.”

Jennifer Frazer September 17, 2010 at 4:30 pm

Amen to that, Sister. :) I agree with you on both counts.

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