no see um

/ˌnoʊˈsiːəm/
noun
  1. A very small biting insect, such as a midge or gnat, that is difficult to see.
    • Campers often complain about no-see-ums more than mosquitoes because their bites itch terribly.
    • We had to wear bug spray to protect ourselves from no-see-ums at the beach.
    • No-see-ums are so tiny that they can get through window screens.
Synonyms
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