Look up "Irukandji". I don't know if I saw the same show as you're talking about, but these things are tiny, invisible buggers. Despite trying to cover every piece of exposed flesh, those two Irukandji researchers both got stung on a dive together and were in full-body agony. Luckily they got out of the water before they were incapacitated with pain. They said that even max doses of morphine only took the edge off the pain. The woman was in severe pain for weeks IIRC.