I regret to sound bigoted in this matter, but the only good deerfly is a dead deerfly. Deerflies are the pornography of the insect world; they possess absolutely no redeeming social value. Deerflies are minuscule winged Al-Qaeda warriors, chanting (in tiny, high-pitched voices) “Death to the earthbound!”
I suppose some brave soul could undertake the research necessary to determine the average lifting capacity per deerfly. Faced with a request to participate, however, I must reply: “Include me OUT.”
Please, my dear ETF, take no offense to my aforementioned suggestion. I was merely extolling the virtue and benefit of the calculation for risk-assessment purposes, and your own well-being. I would sincerely despise the day that I hear in passing, that you and your hoofed companion were brisked away against your wills by the menacing, collective mindset of the oversexed, abhorrent, pestillent airborne hell-spawn.
As a fellow lover of the sylvan trail, I would seek more to eradicate, rather than understand the creatures.
Does Demon WP work on horseflies?
Maybe if we could coax the damned hellspawn to the Pit, we could flame them out of existence?
I’m not sure. I think generally the thing that works best with most nasty little creatures like that is napalm. At least it gives good satisfaction, and you can make it at home, so you avoid having to purchase bug-killers.
The other thing that is satisfying, especially when the fly has been unusually annoying, is to wound it just enough that its escape mechanism is no longer functional. Wounding a housefly just enough that it can only half buzz around in circles on the floor. Now that is satisfaction.
Now, combine the two methods: wound the fly a little bit, then torch it with a bit of home-made napalm. There is some fun the whole family can enjoy!
Or I suppose we could always use a
(Wait for it)
(You knew someone would say this eventually)
1920s style death ray on the deerflies!!! 
Though I don’t claim to be an expert on the 1920’s-style “death ray,” I believe you might not be able to focus the ray as effectively as needed for frying the deerflies.
I believe you could still find a 1930’s-style “bug spray” to be somewhat effective though.
But if you insist on the “death ray,” then go with the beta model EZ-2000 miniature intergalactic warp-driven “bug blaster” (circa 1940). Its really just a scaled-down model, but much better for pinpoint accuracy.
And, of course, for all your death ray needs, there’s no better place than Golden’s, in beautiful downtown Jersey City! 5 stories, filled floor to ceiling with death rays! Prices are always cheap, and all the new models are always in stock! If you live in the NYC area, remember that Golden’s is the one!
I find it difficult to get all the way to the NYC area when my death rays need maintenance, or when I am jonesing for the latest model. Does Golden’s have other locations convenient to me, or perhaps a catalogue that I can receive?
Flit was popular during that decade. Here is a page featuring a bunch of Flit ads drawn by some guy named Ted Geisel.
Good old Teddy. I loved those books. I never knew he did ad work though.
I always liked The Sleep Book the best I think. Was that what it was called?
I hate the flies!
Upon them lies
A guilt of size
To goggle eyes!
Their vicious bite
Gives horses fright
Too late! I smite
The nasty mite.
If I could see
A way to free
The world from the
Bug-ocracy
I would be thrilled!
When all were killed
The buzzing stilled
Fly graveyards filled!
Until that day
Alas, I pray
Flies, STAY AWAY
Or you will pay!
[sub]with apologies to T. Geisel[/sub]
Do you hate the flies today?
Are they always in the way?
Will you take your vengeance now?
“Yes I will” you say, but how?
Will you fire a loaded gun,
in hopes of killing even one?
Could you kill them with a spoon?
Or would you use a big harpoon?
You could bash them with a rock,
or crush them underneath your sock.
A napalm bomb would do the job
of killing an entire mob.
Nuking them would do the trick,
But you would end up very sick.
Would you swat them on a horse?
Would you swat them with great force?
Indeed, I would, of course, of course.
I think that I shall never spy
An ogre loathesome as a fly.
But if you do, I hope you will,
take your vengeance on him still.
You really, REALLY don’t want to know. 
All right, I’ll take your word for it then.
Oh, well, if you insist on knowing, here is some information on the wretched things. I hates them, so I do!!! :mad:
The real question is:
How far can a deer fly?
Depends on the size of your trebuchet.