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Photo#142455
Who am I? - Acrocera bimaculata - female

Who am I? - Acrocera bimaculata - Female
Near Ruraldale, Upshur County, West Virginia, USA
May 24, 2007
Size: 4.5 mm
Can anyone provide an ID? Found walking on the paving stone. Measured 4.5 mm long. One thought I had was Small-headed Fly, but I'm not sure that fits.

Moved
Moved from Neolasia purpurata.

Moved
Moved from Small-headed Flies.

looks like an Acrocerid to me
looks like an Acrocerid to me... not the beest perspective, would like to see more of the head and the antennae...

 
Acrocerid
Thanks, Martin. It is my first in this family if indeed it is an Acrocerid. Too bad the head is so tucked under.

Odd little appendages on the rear of the abdomen!

Thanks for your help with this fly.

 
Very large disk-like calypters too...
...visible between the wing bases and the metathorax. That's also a strong Acroceridae trait (along with small head and bulging thorax).

 
Beautiful!
Looks like Neolasia purpurata (Acroceridae)

 
Thanks
Dennis, thanks very much for the ID!

 
Acrocera bimaculata
Sorry Stephen, I should have looked closer at the wing venation. Its too reduced to be Neolasia. Something about the picture kept nagging at me that appearances can be deceiving. Based on the venation (key character), infuscated wings, the brown legs, overall configuration and size I am now sure that this is a female Acrocera bimaculata. The only thing that can't be seen in the picture are the two small spots that should be located at the sides of the tip of the abdomen. Because this is a female (note the prominent genetalia) the tip of the abdomen tucks under a bit.

 
Re: "Odd little appendages on rear of abdomen" and "Calypters"
Revisiting Stephen's second comment in this thread...I too was curious about those 'semi-abutting right-triangular' appendages visible at the rear of the abdomen. I guess Dennis has addressed our curiosity in his last sentence above by refering to them as part of the female's prominent genitalia.

Also, while we're at it...Dennis, could you correct or confirm my use of the term "calypters" for the transparent discs that are apparent here between the metathorax and the bases of the wings? I'm fairly sure that's what they are, but I've had a nagging doubt because they always appear to be attached to the metathorax in the images I've seen, while all the diagrams in texts show them as a clear basal lobe of the wing. (Haven't had an opportunity to actually examine a specimen in hand and probe this subtlety:-) Thanks!

 
The females have been noted t
The females have been noted to hover over the ground or appropriate substrate and "flick" eggs with the modified ovipositor. The 1st instar larvae "jump" and are quite active in searching out their host. Still this is a dangerous and difficult proposition. So the females produce large numbers of eggs to increase the probability of success.

The large discs are indeed calypters (sometimes referred to as "squamae").

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