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Photo#374717
March Fly - Bibio vestitus - female

March Fly - Bibio vestitus - Female
Marin County, California, USA
March 4, 2010
Size: 13 mm body length
This fly was found dead in some water. None of the other Californian Bibio sp. on here seem to have red legs.

Images of this individual: tag all
March Fly - Bibio vestitus - female March Fly - Bibio vestitus - female March Fly - Bibio vestitus - female March Fly - Bibio vestitus - female March Fly - Bibio vestitus - female March Fly - Bibio vestitus - female

Moved
Moved from Bibio.

I think...
I may have solved this conundrum. I've been catching and examining the march flies that have been falling into the pool, and found that there are females with 5-6 antennal segments and other females with 8-9 antennal segments. I believe these represent the two similar species, B. xanthopus and B. vestitus; the ones with more segments in the antennae did have shorter inner spurs on average, but they frequently overlapped in size and I don't think this is a very good characteristic to go by alone.

I found it difficult to count the antennal segments on the males because they are about half the size of the females and some of the segments appear to be partially fused. I'll have to look at them under a microscope next week. Here is a photo of one of the females with a greater number of segments in the antennae, and I also outlined the tibial spurs:



I think it is safe to call this fly B. vestitus based on the combination of the antennae/spurs. Any opinions?

 
Males
Do you have any pictures of males? I found one which ought to be B. vestitus but it looks unlike your females. The males are supposed to have dark femora.

 
B. vestitus
Based on what you wrote I think you can move this to the B. vestitus page.

Bibio vestitus or xanthopus
This looks like Bibio vestitus or B. xanthopus. Females are distinguished by the length of the inner spur. I linked the key to California species from the genus info page.

 
Re: Bibio vestitus or xanthopus
Thanks! The key has been a great help. I'll get some more photos of the spurs either today or Monday (the latter more likely). The seventh part of the key mentions that B. xanthopus has ten-segmented antennae, though -

"Larger species, wing length typically 7.5 to 9.5 mm.;
femora rufous in both sexes, hind basitarsi slender;
antenna ten-segmented; last two palpal segments three
times as long as wide. (fig. 9c) xanthopus Wiedemann (p. 188)"

Does that apply only to males or to both sexes?

 
Not sure
I think only males ever have swollen hind basitarsi. I don't know if the sexes have different numbers of antenna segments.

 
I'll have to check tomorrow...
These guys have been abundant in my yard for the past week or so, so I'll catch both males and females and try to count the number of segments in the antennae. It seems like the length of the inner spurs on the tibiae could only be diagnostic if they were extremely short, because the key mentions that those of B. xanthopus are occasionally up to two-thirds as long as the outer.

Diagnostic features
Species ID relies heavily on

1. Relative lengths of front spurs (inner much more or much less than half as long as outer are the common cases)

2. Length of R-M crossvein (similar to base of Rs, or much shorter)

After that shape of female head, number of antenna segments, and body hair and wing color are used.

 
Re: Diagnostic features
Thanks for the info, John! I got some more photos in the lab after I pinned it. Unfortunately, the insect was already extremely stiff and brittle (despite it coming from the water), and I accidentally broke one of its hind legs off despite me being as careful as I could. Also, since I couldn't really move the legs to put the insect on a flat surface, the pin is kind of crooked. Ugh. The it's not the greatest example of pinning, but it's only my third time doing it.

Here's what I can determine from the photos I took:

Spurs - Inner spur is longer than half the length of the outer spur.

Crossveins - I'm not sure which one is the R-M crossvein, but I'll upload a shot of the wing.

Head - Flat. I'm not sure how it's supposed to compare to other species.

Antennae - Five segments, that I can tell from the photos.

Hair - Appears to be pale yellow.

Wings - There is a dark streak going lengthwise down the wing, with an even darker spot above that.

Hope this helps some, and I'll go upload the other photos here.

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