Posted June 8th, 2009 by John Callender

I headed to the marsh yesterday with William. My official goal was to examine the terminal bud galls on the coyote brush to see how many of them had emergence holes, and to see if I could find any adult Rhopalomyia californica midges hanging around.

The first thing we noticed at the marsh, though, was this tire near the northern Ash Avenue entrance. My guess is that someone just dumped it there, but maybe there’s more of a story behind it?


On the midge question, my (very rough) sense of things was that about half of the dozen or so galls I looked at had visible emergence holes. At one point while examining the terminal bud of a coyote brush (a bud that did not have a gall), I saw a small, black, winged insect climbing around, and I wondered if it might be a gall midge. It certainly looked fly-like, and was about the right size, judging by the emergence holes in the galls I’ve looked at. I tried to get a photo, but couldn’t get the focus right, and can’t see the insect in any of the shots I took.

A little more googling for information about the midge turned up an article from the Annals of the Entomological Society of America, titled Portrait of an Ephemeral Adult Stage: Egg Maturation, Oviposition, and Longevity of the Gall Midge Rhopalomyia californica (Diptera: Cecidomyiidae). Quoting from the abstract:

Observational and experimental studies in the field demonstrate that this midge typically completes its entire lifetime reproduction in a single day: females usually emerge at dawn, mate, and after a posteclosion period of resting, they initiate a sustained period of active oviposition during which most eggs are laid over a 4–5-h period. Mean longevity of adult females is very short, consistently <1 d and only 5–6 h on clear and warm days.

I had no idea the adult midges were so short-lived: The females emerge as adults from the gall with their eggs fully formed, mate, deposit their eggs, and die, all within a single day. I guess that means I have my work cut out for me in terms of finding an adult gall fly.

As often happens when I visit the marsh, the thing I went looking for wasn’t the most interesting thing I found. Instead, my big discovery was how clear the water in the Franklin Creek channel was. You could see all the way to the bottom across the whole width of the channel, and William and I had great views of fish swimming under the footbridge.

Here’s a shot I took that shows five fish swimming in a line from the bottom of the frame toward the top. They were about 18 inches long; I think they might be striped mullet (Mugil cephalus):


Obviously, when I talk about how clear the water was, I’m talking in relative terms. Normally I can’t see the bottom at all, or see fish that are more than a few inches beneath the surface, so this view qualifies as exceptional in my book.

I also got several shots of what I think was a round stingray (Urolophus halleri). The ray was about the size of a dinner plate:


Here’s another shot I got just as the ray was swimming into my shadow. Unfortunately, I didn’t include the entire ray in the shot, but this gives a pretty good view of its coloration, including the big, pale spots on its body:


I’m not sure why the water in the creek was so clear yesterday. We had some light, unseasonal rain last week; maybe that brought some fresh, relatively clear water into the creek channel? In any event, it was really neat to get a good look at what was going on under the surface.

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