Archive for June, 2009

Valley Carpenter Bee (Xylocopa varipuncta)

Thursday, June 18th, 2009


(Wikipedia image by Matthew Field.)

I’ve noticed this bee several times over the past few years: gigantic (bumblebee-sized or bigger), a beautiful golden color all over, with a habit of hovering for minutes at a time, pausing a few seconds in one place, moving a few feet, hovering again, and repeating, in a circuit that causes it to cruise a limited area over and over. Every time I’ve seen it engaged in this “hover patrol” it has been near some flowers being visited by ordinary honeybees, but I’ve never seen the giant golden bee actually land. I might be reading too much into it, but I get the impression that the bee is aware of me; it seems to face me and check me out, then decides I’m uninteresting and moves on.

I’ve seen this bee in our front yard in Carp, and outside the office building where I work in Santa Monica. (I’ve mentioned my ridiculously long commute, right?) Last Sunday William and I watched one patrolling outside some condos on Sandyland Road, as we walked from the State Beach campground (where we spent the night Sunday night) to the marsh and back.

I asked William what he thought the bee was doing. What’s up with that ceaseless patrol? It has to have a reason, I argued. The bee wouldn’t devote all that energy to the behavior unless there was some point to it.

I’ve tried to google for information about the bee before, without success. Today I tried again, and hit the jackpot.

The bee is the Valley carpenter bee, Xylocopa varipuncta. I’m used to seeing the female patrolling the eaves of houses and other wooden structures, looking for good spots to make a nest hole, and I knew that big black bee was a carpenter bee, but I never realized that this big golden bee was the male of the same species. An article from the UC Davis Department of Entomology quotes entomologist Lynn Kimsey as follows:

Carpenter bees, measuring about an inch long, are the largest bees in California. Their eggs are the largest of all insect eggs. The Valley carpenter bee egg can be 15mm long.

The males are territorial, Kimsey said, and can be quite aggressive. They hover and lie in wait for passing females.

“Female carpenter bees sting, but the males don’t have that apparatus,” Kimsey said. “You can pick up the fuzzy males and they won’t sting you.”

User INaturalist at posted this great image of the bee:


INaturalist wrote:

These big chubby guys come out in the spring and fly around in the willows where Coyote Creek flows into the percolation ponds. In Sunnyvale I find them in the Baccharis at the WPC ponds. They have a very short flight season — a couple of weeks and they’re gone. The females are black and yellow. This one is a drone — presumably its only function is to mate, so what is it doing patrolling? Waiting for a receptive virgin queen to emerge?

I think INaturalist’s speculation is probably right: The bee is on the lookout for females, and is patrolling a territory he’s staked out that seems likely to attract them.

So: Another mystery solved. :-)


Monday, June 8th, 2009

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.


Tuesday, June 2nd, 2009

I was walking at the Carpinteria Bluffs with William the other day, and noticed this on a coyote brush:


I think it’s an old, dried-out bud gall from the same midge I mentioned previously, Rhopalomyia californica. I like that you can see what I assume are the holes made by the adult midges when they emerged from the gall. I’m curious what the adult insect looks like. I’ve tried googling for images of it, but so far I haven’t found any. At least I have an idea of how big they are: just big enough to squeeze out of those holes.

Here’s an image I did find: Blogger user Raphael posted it in an item about wetland restoration at Shoreline Park in Long Beach:


This gall, which is still on a living plant, shows the same emergence holes as my dried version. I wonder what it looks like when the midges emerge. Do they all come out at the same time?

I’d really like to see that some day.

Update: They do emerge together. Check out this amazing series of photos taken by Charles Baughman on March 28, 2010, of a bunch of adult Rhopalomyia californica emerging in Boulder Creek in Santa Cruz County: Coyote Brush Bud Gall Midge – Rhopalomyia californica.

Later update: I take back part of what I wrote above: I don’t think those photos by Charles Baughman show adult midges emerging. I think they show the spent exuviae left behind after the emergence. Still beautiful and amazing images, of a phenomenon I’d still love to see firsthand. As I write this, at the tail end of 2010, we’re coming up on R. californica emergence season. I’ll make a point of checking those galls over the next several months, and see what I can find.