A stinging insect mystery...?

Blister bugs are a possibility. They are a beetle that squeezes an oil out of its leg joints when agitated. This is my best guess since the caterpillars I know that could do this do not fly or move very fast so I could not think of how they would get on your arms.

If you are going through weeds their is an aphid (a red one) that causes such a rash on sensitive people (perhaps my only allergy). But since they are basically stationary and live on weeds, you would have to brush up against the weed directly to come into contact with them.

Blisterbugs often do not give any indication. They are often completely unnoticed until after the event and they tend to fly around at night.

I know this because they were the source of the problems a field trip were having. I had been seeing some and people had been affected. When I suggested the cause they didn't believe me. What convinced them is that they began paying attention to where they landed and sure enough there would later appear the blister. The problem is even though each species is different, most leave a 'blister' sort of like a burn. Therefore in your case I am not sure they are the problem. However since each species is different then this may be a local species' affect.

During the day they stay put feeding on their patches of weeds in large groups.

It really doesn't sound like an insect to me - you say you felt nothing after all, and every insect I know of that causes a reaction does so in an obvious and noticeable fashion. It sounds like a reaction to something, but exactly what beats me. Something must have come into contact with you, and whatever it was, it had some kind of surface material that you have a reaction to. I can't say whether it was some gossamer silk strand, or some sort of liquid spray or something even more exotic. Of course, this is Florida, home to more bizarre exotic invaders than anywhere else on the planet, it seems, so you may want to get in touch with your closest extension office or University bio dept. There is a tree called the Florida Fish-poison tree that produces a very nasty contact oil, or conceivably it could be small droplets falling from a vine like Poison Ivy if you were walking under something at the time. I don't really think this is the answer, but it seems a touch more likely than an 'unfeelable' insect. Good luck!

I agree with the blister bug theory. They are exactly as he described. They are from the family Meloidae. Their hemolymph contains cantharadin, which causes blistering when it comes in contact with out skin.

sparkling each and every of the foliage away out of your living house this is the place animals and bugs prefer to stay... seal any openings into and below your living house and then try posting this question in an element different than politics.

Sounds like an outbreak of hives to me!!?

Or heat rash!!??

Or you are allergic to a certain pollen!!?? (This can be sudden... and you don't necessarily have to have been previously allergic!)

See a doctor... he'll probably give you a course of

anti-histamines.