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Posting on behalf of a neighbor who asked:

Can anyone identify this insect? It's about 3/8" long. There are, it seems, hundreds flitting low over our lawn. There were none 2 days ago.

This is the Northern California Bay Area Peninsula.

Insect

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  • $\begingroup$ $\frac{3}{8}$'' is a weridly accurate measure so just to confirm, it was $\frac{3}{8}$ of an inch, that is 0.95 cm, is that right? $\endgroup$ – Remi.b Oct 1 '16 at 1:16
  • $\begingroup$ Yes, " indicates inches. So about 1 cm. $\endgroup$ – rrauenza Oct 1 '16 at 3:15
  • $\begingroup$ One concern is that they are swarming termites. $\endgroup$ – rrauenza Oct 1 '16 at 14:51
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Great pictures. First, fly or wasp?

In the second picture, under the head you don't see jaws of a wasp, but do see a bit of a tongue-like organ, like a fly. Further down, you can see that there are only 2 wings. Just below where the left wing meets the thorax, you can see what looks like a tiny wing or paddle. That's a haltere, a reduced wing that vibrates to provide stability, like a gyroscope. Flys have halteres. Finally, in the first picture at the very end of the abdomen are 2 points. That ain't a stinger, it's an ovipositor. It's a fly, female, and from the size of the abdomen, gravid.

The closest I've gotten to identifying this one is Axymyia furcata http://bugguide.net/node/view/1216479. Everything matches, as well as we can see from a photo, except the coloration. Also, A furcata is associated with streams and is found in the north-east and north-central US, while, your bug was found on a lawn in CA. For more information about A. furcata than you need, there is a master's thesis available: http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1882&context=etd.

I've looked at hundreds of fly pics to find the one I linked to above. That's the only fly I found that matches the shape of yours. Maybe it's a different fly within that genus, maybe it's just a color variation.

Their maggots live in rotten wood and decaying plant material, and the adults are mostly interested in more maggots, so this isn't a pest, just a neighbor.

Edit: furicata --> furcata, oops.

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  • $\begingroup$ Can you fix furicata to furcata? (I can't -- the edit isn't large enough.) $\endgroup$ – rrauenza Oct 2 '16 at 4:14
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My neighbor submitted the photo to http://bugguide.net and it was identified as a sugar cane soldier fly, "Inopus rubriceps"- Female

http://bugguide.net/node/view/1299782

They are from Australia and were accidentally introduced to San Francisco 50 years ago. It feeds on grasses.

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