From Newsgroup: sci.physics

Why do horseflies need geometry to bite? https://pmc.ncbi.nlm.nih.gov/articles/PMC5717639/

Horseflies cannot reliably identify a host without polarization cues.
It's all about right triangles and the arc tangent of skin.

FACT:
1. I get bitten by horseflies when I leave the pool.
2. They fly around me and then bite my shiny wet skin. Why?
3. It's all about geometry. They bite only when the geometry is right!

a. Brewsters angle is an arctan of the normal vector.
b. n=1.4 for skin. The arctan(1.4) is about 54#
c. So Brewsters angle is 54# for skin.

A. Point your finger at the sun
B. Move it 36# to one side
C. Now the "normal" vector is 54# from the sun

If a horsefly is at the other side of that 54# normal, it bites you.
It flies around, literally, until it "sees" that "laterally polarized" reflection at 54# to the normal vector. Then it bites.

What can you do about it?
Dry your skin and rough it up and then paint it with zebra stripes.
Oh, and sit in the shade.

Moral of the story?
Horseflies don't find hosts by color or heat; they find hosts by geometry. Never give a horsefly the 54 degrees it wants!
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From Newsgroup: sci.physics

rbowman wrote:

Just wear the wingman all summer long - horse flies and
deer flies will leave you alone - as will your friends and family :

https://www.leevalley.com/en-ca/shop/garden/pest-control/insects/110311-

dragonfly-wingman-deer-fly-and-horsefly-deterrent

Could be worse... Nessmuk (George Washington Sears) was a 19th century author who wrote 'Woodcraft' and magazine articles. He had a recipe for an insect repellent that included pennyroyal oil, castor oil, and pine tar.
He advised you to apply in frequently until you built up a good patina. It probably would have repelled bears at that point. Nessmuk was big on solo canoe trips through the Adirondacks.

I read an article yesterday about a new repellent derived from catnip. It advised waiting until you left to apply it if you happened to have cats lurking about.

Apparently even Pliny the elder, in Mount Vesuvius time frame, complained
about the damn gadflies (gad meaning spike, although I don't know if the
word existed at that time).

I am trying to build a trap.

Black ball (which I don't have yet).
Covered in roofing tar (sticky and cheap)
Hanging from a string (moving object)
With a cone on top (funnels the flies up)
And a soda bottle at top (traps them)

It's complicated but it might work.
Anyone ever build a horsefly trap at home?
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From Newsgroup: sci.physics

Maria Sophia <mariasophia@comprehension.com> wrote:

rbowman wrote:

Just wear the wingman all summer long - horse flies and
deer flies will leave you alone - as will your friends and family : >>
https://www.leevalley.com/en-ca/shop/garden/pest-control/insects/110311-

dragonfly-wingman-deer-fly-and-horsefly-deterrent

Could be worse... Nessmuk (George Washington Sears) was a 19th century author who wrote 'Woodcraft' and magazine articles. He had a recipe for an insect repellent that included pennyroyal oil, castor oil, and pine tar. He advised you to apply in frequently until you built up a good patina. It probably would have repelled bears at that point. Nessmuk was big on solo canoe trips through the Adirondacks.

I read an article yesterday about a new repellent derived from catnip. It advised waiting until you left to apply it if you happened to have cats lurking about.

Apparently even Pliny the elder, in Mount Vesuvius time frame, complained about the damn gadflies (gad meaning spike, although I don't know if the
word existed at that time).

I am trying to build a trap.

Black ball (which I don't have yet).
Covered in roofing tar (sticky and cheap)
Hanging from a string (moving object)
With a cone on top (funnels the flies up)
And a soda bottle at top (traps them)

It's complicated but it might work.
Anyone ever build a horsefly trap at home?

What are you going to do with them when you catch them?

Do you think they can be trained to pull little horse carts?
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