---

At first I thought this was Musca autumnalis, but the longer I look at these pictures, the less sure I am. I read a number of old topics on the differences between M. autumnalis and M. domestica, and now I'm inclined to think that this fly (photograped on March 4th at Leerdam, Netherlands) is domestica. But I'm not sure. Or could it be something else althogether?

Thanks in advance for your help.

---

pic 2

---

pic 3

---

I would say, domestica


Theo Zeegers

---

O.k., thanks Theo!

---

Hello,
the orbital plates are too broad for M. domestica. According to my key, they shoud not exceed 1/3 of the frontalia. Here, they are nearly equal. So, in my mind, it would better be M. autumnalis.

Regards.

---

Thanks for your opinion on this one, Stephane.
I read about the identification mark concerning the width of the orbital plates and frontalia in an old thread. Still I got confused: where does one measure the orbital, on top of the head or at front, next to the antennae?
I also got confused looking at the pictures of female autumnalis in the gallery, where Jorge's autumnalis seems to have far less broad orbitals than Crex's.
I also got the impression from a discussion in an old thread, that a broken costa is a specific feature of domestica. My fly seems to have one (pic 2). Or did I get that wrong?

---

Jan, this is one of the problems. I would tend to measure the frontalia and the frontal orbitals across the top of the lunule.

Now the other issue is that the frontalia (as in your photo) is not nearly as well defined as pictures in books would lead us to believe. However, I get the frontalia to measure about 7 mm on my screen, while the orbital measures about 2mm (at the level of the lunule). On that basis I would say this was M. domestica: (Fonseca, 1968: "female frontalia three times as wide as a frontal orbit") compared to M autumnalis, which is less than twice".

What is really needed to differentiate M. domestica from M autumnalis is to be able to see the Propleural depression (in front of and below the anterior spiracle). In M. domestica it has black setae in M. autumnalis, it is bare.

Sadly in photos this is seldom visible, so you're left guessing. The characters of the frontalia are somewhat more comparative and sometimes need a specimen of each in front of you before you can decide.

I hope this helps rather than clouds things.

---

P.S. I don't know how that winky smiley got in there .. that was supposed to be a semi-colon ...

---

This certainly helps, Andrew. I was already afraid I was the only one who had difficulties determing where the orbital plates stop and the frontalia begin :o
Last year I made some pictures of a few evident female autumnalis, with obvious, broad white orbitals. And although at first glance the orbital plates of this fly seemed broad, I began to wonder more and more if what I thought were the orbital plates, were perhaps in fact part of the frontalia.
Thanks very much for helping clearing things up!