The Stream Doctor

November 11th, 2002

Your questions and answers about everything stream related.

Q. From Steve in Sunnyvale, CA: What are the small globs found on stones; the globs are slimy and contain white, egg-type material? They are about 1/2" to 3/4" in size and stick tightly to the rocks that I lift from my favorite streams. They could be insect eggs, but I'm curious as to what the material is that contains them.

I read something about these someplace, but can't remember where. My wife, 9-yr old son, and I are amateur entomologists and like to spend time in the water researching and bring home samples of all types of aquatic life forms for study under a microscope. Entomological techniques I have learned over the past five years or so are quite fascinating. If nothing else, my boy will get a short education and, hopefully, develop more interest down the road.

A. Without actually seeing what you have means I'll have to stick my neck out a bit, but there are a couple of things you might have.

The most likely identification is just what you suspect aquatic insect egg masses that are found in various shapes and forms attached to rocks. The slimy matrix can be clear, red, brown, yellow, or white and serve to hold the eggs in place until they hatch into nymphs or larvae. The matrix that you asked about is a gelatinous polysaccharide, one of a group of complex carbohydrates.

Now, there is one other type of small, mucilaginous nodule found on stones in some streams. These are usually dark green in color and are colonies of the cyanobacterium (formerly called blue-green algae) genus Nostoc. These clumps can be from pin-head size up to the size of a walnut. One form is somewhat "ear-shaped" and contains a midge larvae. One interesting aspect of these organisms is that they can "extract" atmospheric nitrogen (N2), whereas green algae and diatoms can only use nitrogen after it has been transformed into nitrates or ammonium.

Good luck to you and your family in your stream studies. ~ Stream Doctor

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to stream-ecology directly to him for use in this Q & A Feature at

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