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soldier fly - Odontomyia tumida - female

soldier fly - Odontomyia tumida - Female
Benton Crossing Road near alkali lakes, Mono County, California, USA
August 10, 2017
Found on flowering rabbitbrush. Odontomyia?

Images of this individual: tag all
soldier fly - Odontomyia tumida - female soldier fly - Odontomyia tumida - female soldier fly - Odontomyia tumida - female soldier fly - Odontomyia tumida - female soldier fly - Odontomyia tumida - female

Moved tentatively to Odontomyia tumida
Moved from Odontomyia arcuata-group.

From the relevant keys and descriptions, it appears clear that this is either O. tumida or O. arcuata.

The somewhat swollen face (i.e. wider and more forwardly projecting than arcuata) and the pattern of the black tergal markings seem to suggest tumida over arcuata here.

Moved from Stratiomyini.

This indeed keys to Odontomyia in the MND(1)...since the "cross-vein r-m is present": as can be seen in the full-size image as the short "stalk" connecting the small, hexagonal discal cell the the longitudinal vein anterior to the discal cell. (See this wing diagram...and compare to the wing diagram for Hedriodiscus, where r-m is absent and the discal cell is directly touching, or confluent, with the radial vein).

Sufficient details are discernible in the images here to go all the way through the Odontomyia key in James(2)(1936), ending at O. arcuata. The discussion of that species therein suggests its determination was considered difficult and certain characters mentioned there don't exactly match here. I don't know whether species circumscriptions are "settled" yet here, and I noticed that there is no current guide page for species O. arcuata. But there is a guide page for the "arcuata group" which this undoubtably belongs, per the key to species groups at the bottom of page 521 of James(1936).

So I'm unsure whether this post should be placed in a new guide page for species O. arcuata or not...even though that's pretty clearly where the key in James(1936) leads here. Maybe a stratiomyid expert can clarify that issue?

thanks Aaron!
Very helpful.

I'm now mostly convinced this is Odontomyia tumida
My earlier assessment of O. arcuata (sensu stricto) was based the long key in James(1936)...where O. arcuata and O. tumida come out in the very last couplet at the end of the key via:

28. Face in lateral profile extending forward as far as width of the eye; abdominal bands never contiguous .......................... tumida Banks28'. Face in lateral profile extending forward much less than the width of the eye; abdominal bands often contiguous.............. arcuata Loew
From your profile shot, I measured the face extending forward a bit more than half the eye length (i.e. 7/13 ≈ 0.54, or "much less than the eye width"), so I went with arcuata. I carefully went through the keys in James(1960)(1), and found that, using that reference, your photos lead to genus Eulalia (= Odontomyia), and species E. tumida. There the couplet separating tumida from other members of the "arcuata group" is:

11. Lower occular orbits divergent (figs. 34, 35), the sides of the face in the female, as well as in the male, likewise divergent; face entirely yellow except somtimes two small spots above the tentorial pits; abdominal terga with black transverse basal bands, strongly biarcuate posteriorly, in both sexes, those of the male connected on a median line with those of adjacent segments....tumida11'. Lower occular orbits, along and just above the oral margin, parallel (figs. 31, 32); sides of face of female approximately parallel; face often marked with black or wholly black. ................12 (leading to inaequalis, communis, alticola and arcuata)
The face and lower (inner) margins of the eyes in your photos appear divergent, and indeed they match the female of tumida shown in Fig. 35 of James(1960)(1), better than the female of (arcuata) communis shown in Fig. 31. And, even better than those figures from James(1960), consider the frontal type specimen images below from the MCZ:

      tumida Odonotomyia tumida from MCZ         arcuata Odonotomyia arcuata from MCZ

In addition to James(1960), I was also able to obtain the key in James(1974), where your post here goes promptly to tumida, via:

1. Sides of face broadly diverging all the way to the lower margins of the eyes; in males, distance between the lower angles of eyes distinctly longer than vertical distance from that plane to bases of antennae ........ 21'. Sides of face parallel or almost so on lower part opposite oral margin, in females slightly convergent; in males distance between the lower angles of eyes no greater than vertical distance from that plane to bases of antennae; eyes bare............3 (leading to cincta, inaequalis continua, inaequalis communis, inaequalis inaequalis, arcuata arcuata, arcuata alticola and arcuata occidentalis)2. Eyes hairy; face marked with black, usually conspicuously so. ................ hirtocculata James2'. Eyes bare; face wholly yellow or green. ................tumida Banks
Note that the character "Face in lateral profile extending forward as far as width of the eye", which was emphasized in the 1936 key...and also appears in the descriptions of tumida given in Bank(1926) [see here] and James(1936) [see here]....was not repeated in the 1960 and 1974 keys. I'm thinking that character was overstated in the keys and descriptions prior to 1936. The epithet tumida is latin for "swollen"...and indeed, studying the MCZ type images below for tumida and arcuata:

      tumida Odonotomyia tumida from MCZ         arcuata Odonotomyia arcuata from MCZ sees the face of the former is more "forwardly swollen" than that of the latter. BUT, the face does not extend forward a "full eye's-width" in the tumida type image...rather it extends 2/3 (≈0.66) the eye width. And while the face extends your photo extends forward only 0.54 of the eye width, it's still substantially "swollen" compared to the type of arcuata.

Another significant character supporting tumida is the shape of the black markings on the abdomen. For tumida they're described in James(1936) as follows:

"segments two to five with black transverse bands which are usually confined to the basal half and never contiguous with the lateral margins nor with the bands of the adjacent segments; those on segments two and three strongly biarcuate on the posterior margins; that on four less so; that on five semi-elliptical"
Your photos very much conform to the above...whereas the description of arcuata in James(1936) indicates its black tergal bands are "often connected medially with the bands of adjacent segments". Again, compare dorsal images of the MCZ types with your female:

      tumida Odonotomyia tumida from MCZ         arcuata Odonotomyia arcuata from MCZ

Nearly everything (keys, descriptions, type images) supports O. tumida here...the only descrepancy seems to be the black markings just above the antennae: as in the type images above, for tumida they're described as being two separate lateral spots contiguous with the eyes; whereas in arcuata they're joined as a single "very broad" transverse marking above the antennae. In your photos the two spots are joined by a narrowed band. This appears to be more in line with the character state for arcuata. My guess it this discrepancy can be attributed to "variation". Overall, the stronger match seems to clearly be with tumida.

One last thing...the following quote is from Cole(2)(1967):

"O. tumida Banks(1926) was described from Calif. specimens and is a rather common autumn species in that state; the known range is from Wash. and Mont. to Kansas. Banks stated that nearly all specimens going under the name arcuata were referable to tumida, but it might depend on the dipterist doing the naming."

Moved from Soldier flies.

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