I didn't like that advice the first time I heard it, on the basis that spraying folks with nerve agent seemed like a bad idea. If you need a less than lethal option, OC spray or Mace, or even one of those crappy stun guns they sell everywhere, would seem like a better idea.
Why? Because the label tells you not to use in an enclosed space, or to evacuate an enclosed space before use. Because these products generally have a warning that says something like "Illegal to use in a manner inconsistent with this labeling" as part of the safety precautions. Because of the possibility of some lawyer standing up in a courtroom and reading the label of the can, and challenging any suggestion that it was "less than lethal". Since you gave and/or took advice that this was useful as a self-defense tool, the issue of liability is greater than I was comfortable with.
Mind you, if you're attacked by a gang while spraying that wasp nest in the back year, it's what you have and they have it coming, but deliberately arming yourself with a bug bomb seems questionable.
I suppose the reason that wasp spray specifically gets recommended is that it shoots what seems to be a powerful stream for a relatively long range, and the target will curl up and drop when hit. It's a (relatively) little bitty bug, hit by a stream that is powerful relative to it's size, and formulated to it's biology.
So when someone said "Wasp Spray", I mentioned that I thought it was a bad idea, and sat back with a metaphorical bowl of popcorn and waited for the experts.
They did not disappoint:
Wasp spray for self defense? This myth just won’t die! – www.GrantCunningham.com
You should read the whole thing, but:
The concentration of pyrethrins in a typical wasp spray isn’t all that high, but the amount of material in the stream which hits the insect may weigh as much as it does; even in a small concentration, the insect will get a huge dose of the poison relative to its weight. The distillates which serve as the carrier are selected to get past the bug’s exoskeleton and deliver the poison very rapidly. The result is the effect described above: the insect loses its ability to control its muscular functions in mid-air and drops to the ground, where it rapidly dies.Mr. Cunningham also links to an American Preppers Network article with a detailed discussion of the chemical make-up of wasp spray, and of the differences between OC for humans and for bears, as well as a link to a news item about a couple who tried unsuccessfully to use wasp spray to "repel boarders" during a home invasion.
When directed at a human, I can tell you from experience this doesn’t happen. As I said at the top, several years ago I managed to spray myself in the face with some wasp spray as I attempted to snuff out a large nest. I wasn’t looking at the can as I shifted my grip to get the spray into an difficult place, and I was wearing gloves so that I couldn’t tell where the button was pointed. Instead of hitting the nest the spray hit my face!
I was in no way incapacitated and had no problem walking into the house, cleaning myself off, and checking the manufacturer’s website for first aid procedures. I did notice some tingling and my vision was a little blurry in one eye for a bit, but that was about the extent of it.
Plus, this video:
So, spraying wasp spray on a news crew filming the news in a public area put them in such distress they thought it was... windshield washer fluid.
Can we please stop the derp?