I recall experiences I had with houseflies when I was a teenager growing up in Raton.
Whenever a housefly ventured into our home, the National Guard was called. My dad was the National Guard. I can still see him — fly swatter in hand, eyes glancing this way and that, until the invader was cited away from food and on a place that Mom would tolerate fly fluids and guts, then — swat. I enjoyed that performance with little concern. At that time in life, my mind was occupied with girls, sports, making a few bucks at my job, what was for dinner, my clarinet, among other important things. Later in life, I learned that I should have been concerned because houseflies cause havoc with human health by infecting them with diseases.
Now I have my own family, and I am the National Guard who holds the fly swatter and glances here and there until the unwanted critter lands on a suitable kill site. Then, I hand the fly swatter to my wife, Marjorie. She makes the kill. She’s good. She rarely misses.
There are good reasons why we should be cautious of houseflies because they do not remain on dead tissue, garbage, and poop. Instead, they move from those items to our foods and transfer disease producing organisms to us, and mouthparts of the fly are responsible for that transfer. Their mouthparts are on the end of a tubular organ which remains withdrawn in the fly’s head when the fly is not feeding. When the fly locates a likely meal, this organ telescopes downward, in the same way we would extend the legs of a tripod, and fleshy lobes on the end of this tubular organ puff out. Imagine this being similar to an air bag being inflated within an automobile. As the mouthparts are being extended, the fly vomits on the food to facilitate digestion. The lobes then press down on the vomit and food, which are both sucked up into openings on the underside of the lobes. When the fly departs from the food source and lands on our food, disease producing organisms are transferred from the flies vomit and mouthparts to us.
Now it is true that houseflies clean their bodies excessively, and they might rid themselves of some of those bad guys. But, to me it is obvious they do not get rid of all of them. So for that reason, I still do not want a fly on my sandwich.
Desert Biologist Tony Gennaro of Portales writes a monthly column on creatures of the Southwest. Contact him at: firstname.lastname@example.org