>> 'persistent bug bite syndrome,'
My first thought was "allergic reaction". For some things, the first exposure is relatively free. Your immune system sees the new allergen and starts to produce cell types that "remember" it and will rush to the rescue the NEXT time you're exposed.
Of course, the "rescue" may be an allergic reaction that is very annoying.
Like hay fever is "protecting you" from the pollen.
But if the spider venom or pollen were terribly toxic, turning red would be better than passing out.
