Prolly both?
http://www.usatoday.com/tech/columni...derquest_x.htm

Houseflies are messy eaters.
Jim Kalisch, Department of Entomology, University of Nebraska-Lincoln

Q: What are the little black dots that flies leave behind all over the
surfaces in my house? (Alison, Lissewege, Belgium)

A: Flies have a disgusting way of feeding. They can't eat solid food since
their spongy mouthparts are too soft to break up food. So, they soften the
victual by spitting on it. The saliva melts the piece of food. They sop it
up like a sponge into their digestive tract. Since the food is already
liquefied, flies digest nutrients fast and soon expel fecal material.

There you have it — the two sources of flyspecks — saliva and fecal matter.
As the fly eats, it scatters spit. Soon after eating, it eliminates waste.

Additional reading:
http://www.ivyhall.district96.k12.il...sects/fly.html

----- Original Message -----
From: "Dave Jackson"
Newsgroups: rec.woodworking
Sent: Wednesday, March 02, 2005 6:46 PM
Subject: WTF?! Fly Puke???


You know, I've used the same dresser pretty much all my life. My
parents
bought it for me when I was very young and it was built in the late
1960's.
It's nothing fancy, just a manufactured colonial style dresser that's held
up well over the years. The thing I've never understood is why there
are
all those dark speckles in the light finish.
I've been reading Jeff Jewitt's book on finishing and just read the
part
on "fly specking". It's a method used to fake damage in a finish. Ahhh,
that's what it's called.
After contemplating this for a few minutes, I finally put two and two
together. Those dark specks look just like the ones the flies leave on
the
windows in my shop! I know, most of you are probably thinking "well duh!"
but here's the situation. Are those specks crap or puke? I'm no insect
specialist, but I've always understood that flies often puke when they
land.
They also have to crap *somewhere*.
Did the manufacturer of my dresser try to imitate fly puke or crap in
the finish???? This sounds asinine! Does anyone have any insight as to
the
real nature of "fly specking"? --dave