Small yellow and black syrphid fly

2009 December 19

While we did find this one inside the house, it was our own fault: he was carried in on some lettuce that we harvested from the garden in August.

For scale, that’s my knuckle he was crawling on, so he was not very big – about 6 or 7 mm long, and pretty skinny.

I was pretty sure that he was a small Syrphid Fly, family Syrphidae. These tend to resemble bees, and the adults hang around flowers eating nectar and pollen (where they are frequently called “flower flies” or “hover flies”). If we look at one wing closely, we can even see that it has the “spurious vein” that is characteristic of the Syrphidae.

At this point, I couldn’t make up my mind about exactly which of the many species of syrphid flies it might be, there were several that I thought looked likely. So I posted it to Bug Guide, and Ron Hemberger identified it as most likely one of the species in the Sphaerophoria genus. Evidently it is hard to get it down to the species without having a specimen in hand to dissect, so that’s where we’ll leave it.

And in the next picture we see exactly why I have been referring to him as “he” – see that structure curling under the end of his abdomen? That’s his male sex organs. Female syrphid flies in this genus just have an abdomen that tapers to a blunt point, with no bulgy bits.

We can also see he’s a male from his eyes. Like other male flies, his eyes are large and in contact with each other across the top of his head, while a female would have eyes that were clearly separated.

The larvae of this genus, like a lot of other syrphid flies, are blobby things that look a lot like slugs. Unlike slugs, though, the larvae are carnivorous, and eat aphids. The fact that something that looks and moves like a slug is actually able to catch and eat aphids kind of says a lot about the limited ability of aphids to flee from predators, doesn’t it?

4 Responses
  1. Ellen permalink
    December 19, 2009

    Fascinating. I will now keep my eyes open for connected (or not) eyes and “bulging bits” the next time I see a Syrphid.

  2. December 25, 2009

    Off topic: Merry Christmas!

  3. December 25, 2009

    And a Merry Christmas to you as well. Merry Christmas Everyone!

  4. Angie permalink
    July 12, 2012

    Do these bugs bite or sting? I’m sitting on my porch, after a particularly soaking rain that we have needed for months, and now all of a sudden these little guys are swarming. I have five on my legs right now. I decided to look them up, because I always thought they were sweat bees. The internet says I’m wrong. I live in a particularly humid area, in western TN, if that makes any difference. But the best I can tell, my bugs are the same as these pictures.

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