Sunday, August 18, 2019

Not a spider

So it wasn't a spider after all. I posted a photo of a spider look-alike a few days ago.

This little guy, about 3 mm. long, on gumweed.

I counted 8 legs, but I sent it in to BugGuide, and they count 6 legs and two antennae, which makes it not an arachnid.*

Ken Wolgemuth, on BugGuide, says it is "an aphid of some sort."

Interesting: I've seen many black aphids, but always in a mass covering stems and leaves of a whole plant. I've never seen (that I knew of) one out for a walk on his own.

Now this, I know for sure, is a spider:

Fat house spider, Steatoda, probably bipunctata, probably female. On the wall above my desk.

*Update: not 6 legs and 2 antennae; they're 6 legs and 2 "corniculi, a pair of tubes that come off the back of an aphid's abdomen," as Christopher Taylor tells me in the comments. He adds that they may be used to release chemical compounds.


From WikipediaThe cornicle (or siphuncule) is one of a pair of small upright backward-pointing tubes found on the dorsal side of the 5th or 6th abdominal segments of aphids. They are sometimes mistaken for cerci. They are no more than pores in some species.
These abdominal tubes exude droplets of a quick-hardening defensive fluid containing triacylglycerols called cornicle wax.
Thank you, Christopher!

2 comments:

  1. What you presumably counted as two of the 'legs' were the corniculi, a pair of tubes that come off the back of an aphid's abdomen. I think they're used for releasing chemical compounds.

    ReplyDelete
    Replies
    1. Thanks! I've updated the post. And now that you tell me, I realize that I've seen these on the aphids in my garden, without knowing what they were.

      Delete

I'm having to moderate all comments because Blogger seems to have a problem notifying me. Sorry about that. I will review them several times daily, though, until this issue is fixed.

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