n.
蜻蜓科的昆虫

[ noun ]
dark-colored insect having predaceous aquatic larvae
<noun.animal>

alderfly \al"der*fly`\, Alder fly \Al"der fly\
1. Any of numerous dark-colored neuropterous insects of the
genus {Sialis} or allied genera. They have predaceous
aquatic larv[ae], which are used for bait.
[Webster 1913 Suppl.]

2. (Angling) An artificial fly with brown mottled wings, body
of peacock harl, and black legs.
[Webster 1913 Suppl.]