How many houseflies would it take to lift me?

June 14, 2013

Dear Cecil:

I weigh 110 pounds. How many trained houseflies it would take to lift me?

Cecil replies:

So what’s the deal, Tanya? You’re in Cincinnati bound for Newark, and they just announced a four-hour delay for your flight? No matter, this is the Straight Dope. We promised the parole board we’d abide by the laws of physics, but within those fairly broad parameters, we’ll see what we can do. As always, we’ll take it step by step:

1. I can’t say I was all that surprised to learn this, but scientists have determined experimentally how much a housefly can lift. It’s about 10 milligrams, or about 22 millionths of a pound. That may not sound like much, but it’s an impressive 50 percent of a fly’s body weight — you try picking up 55 pounds and flying off under your own steam.

2. We know it’s possible to harness fly lifting power because of an inventive and evidently somewhat disturbed aircraft modeler named Frank Ehling, who constructed tiny balsa-wood-and-tissue-paper airplanes powered by houseflies. He would catch one or more flies and stun (or freeze) them, dab glue on their rear ends, and stick them to the plane. When the flies recovered (or warmed up), they buzzed away, pulling the little planes aloft. Two of these aircraft currently reside in the Smithsonian.

3. Practical problems now intrude. Dividing 110 pounds by the lift of a housefly, we find you’d need five million of the insects to lift you off the ground. Not finding this a pleasant visual, Tanya? Hey, it was your idea. The more pressing question is, how will they hold on to you? Assuming a surface area of 17.2 square feet for the average adult woman and a quarter square inch of gripping surface needed per fly, you can only have 39,680 flies sitting on you at one time.

Either flies will have to sit on top of flies (which won’t work, since all but the outermost flies won’t be able to use their wings), or you’ll need to have numerous tiny filaments glued to your body and yoked to sufficient flies to get you airborne. My assistants Una and Fierra initially proposed using 14-pound-test nylon fishing line and concluded the job was impossible, since the weight of the line would exceed the lifting strength of the flies.

“You knuckleheads,” I said. “Fishing line is too bulky. You want spider silk. It’s five times as strong as an equal weight of steel, and the amount needed to circle the earth would weigh less than 500 grams.”

“Where are you getting this from?” Una asked.

Wikipedia,” I said.

“You said not to use Wikipedia.”

“I said you couldn’t use Wikipedia. You’re the engineer. I can use Wikipedia. I’m the big-picture guy.”

“Where are we going to get enough spider silk, and how are we going to tie it around five million flies?” asked Fierra.

“We’ll leave that to the contractor,” I said. “All we have to do is write the spec.”

4. The two returned to their spreadsheets. Assuming spider silk weighs 500 grams per 24,075 miles, they calculated you’d need 4,989,542 flies to take flight.

5. That's a lot of flies. Shall we try bumblebees? Each can lift about 252 millionths of a pound, about ten times as much as a housefly. Total requirement: 437,240 bees.

6. But perhaps bees make you nervous. Better idea: monarch butterflies. Each can carry about 1.7 thousandths of a pound, meaning 65,644 should suffice.

7. Personally I’m charmed at the thought of being conveyed through the heavens by butterflies. Saddling them up would be slow work, though, so let’s consider some brawnier candidates:

  • Rufous-tailed hummingbirds. Lift capacity about a hundredth of a pound — 10,610 needed.
  • House sparrows. Lift capacity 3.7 times greater — 2,910 needed.
  • Jamaican fruit bats. Lift capacity nearly an ounce, 1,915 needed. (At some point surely we’ll need to switch back to nylon fishing line; we’ll let the critter wranglers worry about when.)
  • Common pigeons. Lift about a quarter pound, 441 needed.
  • Bald eagles. Lift capacity approximately 4.5 pounds, 25 needed, although the research department speculates that if the eagles didn’t have to take off with you already in their clutches but could instead be trained to swoop down in formation and snatch you up on the wing, you might be able to get by with 16. I make no promises. I merely observe that if eagles were good enough for Gandalf, they ought to be good enough for you.
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References

Dennett, Richard Edward, and Arthur Everett Shipley. The Shipley collection of scientific papers. Vol. 8 No. 3 Macmillan and Co., Limited, 1910.

Hanser, Kathy. “Insect Power” AirSpace 26 June, 2009. Online edition, accessed 25 May, 2013. http://blog.nasm.si.edu/aviation/insect-power/

Marden, James H. "Maximum lift production during takeoff in flying animals." Journal of Experimental Biology 130.1 (1987): 235-258.

Mountcastle, Andrew M., and Stacey A. Combes. "Wing flexibility enhances load-lifting capacity in bumblebees." Proceedings of the Royal Society B: Biological Sciences 2801759 (2013).

Schilstra, C., and JH van Hateren. "Blowfly flight and optic flow. I. Thorax kinematics and flight dynamics." Journal of Experimental Biology 202.11 (1999): 1481-1490.

Woodford, Riley “Eagle Myths: Big raptors can carry off small pets but they rarely do” Juneau Empire 04 November, 2007. Online edition, accessed 21 May, 2013. http://juneauempire.com/stories/110407/out_20071104001.shtml

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