Friday, December 03, 2010

Pink velvet mite

The tides are high these days, around the delta, at least. High tide alternates with really high tide, then high tide again. The only lows are in the middle of the night. Not till next year does the situation change.

On the White Rock beach yesterday, we found only a narrow strip of pebbles to walk on.  And mounds of rotting eelgrass, tossed up and pressed together by repeated high tides, made a thick wall, separating us from the water. It was so dense I could stand on it without sinking in.

The widest part of the beach.

This "pyramid" is as high as a chair seat.
 I was looking for some fresh, green eelgrass and sea lettuce for my hermits and crabs back home, so I poked around the sea-ward side of the wall. Some of the eelgrass there was still not rotted; that's the best I could say of it. I found a couple of sprays of rockweed.

But all the rest, truckloads, trainloads of it, was made up of torn fragments of brown and black eelgrass, mixed with broken kelp holdfasts, seagull feathers, and rotted leaves from the shore. Oh, and beach hoppers by the thousands.

I gave up and brought home the freshest kelp holdfast I could find, from a pile thrown up above the tide level. The hermits like that, in small amounts; it would have to do.

When I opened the bag at home, several dozen kelp flies escaped. They were too small and too fast to catch; they're gone, I know not where. And checking the holdfast and cutting it down for my critters, I found two tiny pink mite-like things. I managed to capture the largest.

1 mm. long. Trapped upside-down on (not in) a drop of water. I don't know why the drop looks more like a solid pill.
 In the photos, it turned out a yellowish orange. In real life, it is definitely highlighted in pink, baby pink.

Set free, and running away. A fast-moving little beastie.
I thought, at first, that these were the red velvet mites, like the one I saw long ago at Crescent Beach. Except that they should have been really bright red, not pale pink. Still, they're mites, aren't they? And the red velvet hangs out on the upper beach around rotting marine plants, eating small flies. It fitted.

I looked up the red velvets on BugGuide and on WSU's Beach Watchers; except for the colour, they matched. Bumpy oval body, curved legs, long antennae, pointy snout, 1 to 3 mm. long ...

Oh! Except that mites are relatives of the spiders; they have 4 pairs of legs. Mine have 3. Maybe one had broken off? On each side? I checked with the microscope:

Doesn't look like 3 good pair and two stubs.
It took a while, but I found the answer: adult mites have four pairs of legs, but the young ones, before the first molt, have only three. (Kendall, Science clarified, and Science.jrank.) So mine is a baby.* Maybe that's why it's baby pink.

By the way, my menagerie liked the kelp holdfast. The rockweed not so much.

*Update: Christopher Taylor (see comments) disagrees; he says these are clearly 4 legs. The two "antennae" are legs in disguise. I thought of that, but the photo on BugGuide shows two red velvet mites with the 4 legs plus two long antennae. But the ones on BeachWatchers are like mine. Now I'm confused again.

Update # 2: Christopher explains further.
The mites in the Bug-Guide photo you link to are bdellids, a different family to the one in your photos. Unfortunately, I don't know mites well enough to tell you exactly what your one is; I just recognise bdellids because I see them fairly regularly in our own collections at work. In the bdellid photo, the 'antennae' are the long palps. The things in between the pedipalps are the chelicerae, the appendages that are used for actual eating (well, technically they're a forward extension of the body containing the chelicerae). The chelicerae are visible in your mite, but only just: if you look closely, you may be able to see a little triangle between the palps.
To sum up: arachnids have generally six pairs of appendages: chelicerae (used for eating), palps (used for holding and manipulating things), and four pairs of legs (used for walking, of course). Depending on the type of arachnid and the angle of view, the chelicerae may or may not be easily visible; the others usually will be (though some arachnids have very weird palps).
That helps. I went back to BugGuide and back-tracked through the Mite and Tick families. I found Velvet mites, Trombidiidae, that had the proper number of legs and other appendages. I wouldn't pin it down to those, at this stage, but I can see that I haven't been imagining things. (I was starting to wonder about that, today!)

More work is needed.

Thanks, Christopher!

6 comments:

  1. Beautiful and interesting pictures.. i liked..

    ReplyDelete
  2. Um... the mite in your photos very clearly has four pairs of legs. Remember, mites don't have antennae, so the pair extending forward are the first pair of legs. Also, if you look between the first pair of legs you can also see the small palps that are used for manipulating food items.

    ReplyDelete
  3. =) Very interesting post, love how that drop of water looks. And thanks to Christopher for clearing up what I was thinking, too. =) Cleverly disguising legs as antennae, what a crafty little creature. =)

    ReplyDelete
  4. Thanks, Christopher. I thought of that when I was looking them up; I remembered that you'd told me that before.

    The problem is that the photo on BugGuide shows two red velvet mites with the 4 legs plus two long antennae. I looked at all BugGuide's samples of this mite; they all have 4 legs and long "antennae", plus the palps.

    But now that I've gone back to double-check, the ones on BeachWatchers are "three-legged" like mine. Now I'm really confused.

    ReplyDelete
  5. Ah-ha, you're getting confused by bdellids ;-).

    The mites in the Bug-Guide photo you link to are bdellids, a different family to the one in your photos. Unfortunately, I don't know mites well enough to tell you exactly what your one is; I just recognise bdellids because I see them fairly regularly in our own collections at work. In the bdellid photo, the 'antennae' are the long palps. The things in between the pedipalps are the chelicerae, the appendages that are used for actual eating (well, technically they're a forward extension of the body containing the chelicerae). The chelicerae are visible in your mite, but only just: if you look closely, you may be able to see a little triangle between the palps.

    To sum up: arachnids have generally six pairs of appendages: chelicerae (used for eating), palps (used for holding and manipulating things), and four pairs of legs (used for walking, of course). Depending on the type of arachnid and the angle of view, the chelicerae may or may not be easily visible; the others usually will be (though some arachnids have very weird palps).

    ReplyDelete
  6. Thanks so much, Christopher!

    I went back to BugGuide and back-tracked through the Mite and Tick families. I found Velvet mites, Trombidiidae, that had the proper number of legs and other appendages. There may be more; I still have to look them over.

    Odd that the Washington State U site (Beach Watchers) and BugGuide give their mites the same species name; could it be that BW is also confused, or am I not seeing their photos correctly?

    Anyhow, I'm now going back to BugGuide to examine more mites.

    Thanks again!

    ReplyDelete

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